U.S. patent number RE39,711 [Application Number 10/727,331] was granted by the patent office on 2007-07-03 for display device and luminance control method therefor.
This patent grant is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Yuichi Ishikawa, Mitsuhiro Kasahara, Tomoko Morita.
United States Patent |
RE39,711 |
Kasahara , et al. |
July 3, 2007 |
Display device and luminance control method therefor
Abstract
A temperature difference estimated value is found from a video
signal using a temperature estimated value representing the
temperature of the panel outer periphery of a display screen of a
PDP and a reference value representing the temperature of the panel
outer periphery of the PDP which is outputted from a panel
periphery temperature setter by a temperature difference estimator,
and the luminance of an image displayed on a display is controlled
depending on the temperature difference estimated value by a
controller and a brightness controller.
Inventors: |
Kasahara; Mitsuhiro (Hirakata,
JP), Ishikawa; Yuichi (Ibaraki, JP),
Morita; Tomoko (Hirakata, JP) |
Assignee: |
Matsushita Electric Industrial Co.,
Ltd. (Osaka, JP)
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Family
ID: |
17662759 |
Appl.
No.: |
10/727,331 |
Filed: |
December 4, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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09856161 |
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6414660 |
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PCT/JP00/06212 |
Sep 11, 2000 |
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Reissue of: |
09994794 |
Nov 28, 2001 |
06441803 |
Aug 27, 2002 |
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Foreign Application Priority Data
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Oct 4, 1999 [JP] |
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11-283228 |
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Current U.S.
Class: |
345/63; 345/690;
345/211 |
Current CPC
Class: |
G09G
3/2944 (20130101); G09G 2320/0626 (20130101); G09G
2330/045 (20130101); G09G 2320/0271 (20130101); G09G
2320/041 (20130101) |
Current International
Class: |
G09G
3/28 (20060101) |
Field of
Search: |
;345/60,63,204,211,213,589,690 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0888004 |
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Dec 1998 |
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EP |
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0924683 |
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Jun 1999 |
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EP |
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0930603 |
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Jul 1999 |
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EP |
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6-282241 |
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Oct 1994 |
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JP |
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6-289812 |
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Feb 1995 |
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JP |
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9-6283 |
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Jan 1997 |
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JP |
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9-198005 |
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Jul 1997 |
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JP |
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9-288467 |
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Nov 1997 |
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JP |
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10215424 |
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Aug 1998 |
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JP |
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11-15387 |
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Jan 1999 |
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JP |
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11194745 |
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Jul 1999 |
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JP |
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11212517 |
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Aug 1999 |
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JP |
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11219152 |
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Aug 1999 |
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JP |
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11231828 |
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Aug 1999 |
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JP |
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11283228 |
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Oct 1999 |
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JP |
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11288244 |
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Oct 1999 |
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JP |
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2001-200087 |
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Jul 2001 |
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JP |
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99/30308 |
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Jun 1999 |
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WO |
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99/30309 |
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Jun 1999 |
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WO |
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Other References
English Language abstract of JP 9-198005. cited by examiner .
English Language abstract of JP 11-288244. cited by examiner .
English Language abstract of JP 11-231828. cited by examiner .
English Language Abstract of EP 0924683. cited by other .
English Language Abstract of EP 0888004. cited by other .
English Language Abstract of EP 0930603. cited by other .
English Language Abstract of JP 11-212517. cited by other .
An article entitled "A Heat Control Method for Plasma Display
Panel," ITE '98: 1998 ITE Annual Convention, together with a
partial English language translation of the same. cited by other
.
English Language Abstract of JP 6-289812. cited by other .
English Language Abstract of JP 11-219152. cited by other .
English Language Abstract of JP 11-15387. cited by other .
English Language Abstract of JP 6-282241. cited by other .
English Language Abstract of JP 9-6283. cited by other .
English Language Abstract of JP 9-288467. cited by other .
English Language Abstract of JP 10-215424. cited by other .
English Language Abstract of JP 11-194745. cited by other.
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Primary Examiner: Chang; Kent
Attorney, Agent or Firm: Greenblum & Bernstein,
P.L.C.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
.[.This is a divisional of U.S. application Ser. No. 09/856,161,
filed Jun. 1, 2001, which was the National Stage of International
Application No. PCT/JP00/06212, filed Sep. 11, 2000, the contents
of which are expressly incorporated by reference herein in their
entireties. The International Application was not published under
PCT Article 21(2) in English..]. .Iadd.This is reissue application
of U.S. application Ser. No. 09/994,794, filed on Nov. 28, 2001,
now U.S. Pat. No. 6,441,803, which is a divisional of U.S.
application Ser. No. 09/856,161, filed Jun. 1, 2001, now U.S. Pat.
No. 6,414,660, which was the National Stage of International
Application No. PCT/JP00/06212, filed Sep. 11, 2000, the contents
of which are expressly incorporated by reference herein in their
entireties. The International Application was not published under
PCT Article 21(2) in English..Iaddend.
Claims
What is claimed is:
1. A display device, comprising: a display having a display screen
that displays an image with a luminance corresponding to a video
signal and an outer peripheral portion adjacent to said display
screen; a temperature estimation device that provides a temperature
estimation value, corresponding to a temperature of said display
screen, based upon said video signal; an operation device that
determines a temperature difference estimation value using a
reference value corresponding to the temperature of said outer
peripheral portion and said temperature estimation value; and a
control device that controls said luminance on said display screen
so as to lower a maximum luminance of said image as said
temperature difference estimation value increases.
2. The display device of claim 1, wherein said temperature
estimation device estimates said temperature estimation value
corresponding to a temperature of an outer periphery adjacent
portion in said display screen adjacent to said outer peripheral
portion.
3. The display device of claim 1, wherein said display comprises a
first board and a second board whose outer peripheries are joined
to each other, a plurality of light emitting elements that form
said display screen being interposed between said first board and
said second board, said outer peripheral portion of said display
including a portion between said light emitting elements positioned
in an outermost periphery of said display screen and a joint
portion of said first board and said second board.
4. The display device of claim 1, wherein said temperature
estimation value is estimated by integrating data related to said
luminance from said video signal and subtracting data corresponding
to an amount of dissipated heat from said integrated data, said
operation device subtracting said reference value from said
temperature estimation value to determine said temperature
difference estimation value.
5. The display device of claim 1, wherein said image is displayed
on said display screen with a gray scale, selected from a plurality
of gray scales, corresponding to said video signal, said control
device lowering said luminance of said image at a same ratio for
each of said plurality of gray scales.
6. The display device of claim 1, wherein said reference value
comprises one reference value selected from a plurality of
reference values, said plurality of reference values differing from
one another based upon a position of an outer peripheral portion of
said display.
7. The display device of claim 1, further comprising: a measurement
device that measures said temperature of said outer peripheral
portion of said display, said measurement device outputting said
reference value, corresponding to said measured temperature, to
said operation device.
8. A method for controlling a luminance of a display device, the
display device having a display screen that displays an image with
a luminance corresponding to a video signal, and an outer
peripheral portion adjacent to said display screen, the method
comprising: obtaining a temperature estimation value, that
corresponds to a temperature of the display screen, from the video
signal; finding a temperature difference estimation value using a
reference value, that corresponds to a temperature of the outer
peripheral portion, and the temperature estimation value; and
lowering a maximum luminance of the image as the temperature
difference estimation value increases.
.Iadd.9. A display device, comprising: a display having a display
screen that displays an image with a luminance corresponding to a
video signal and an outer peripheral portion adjacent to said
display screen; a temperature estimation device that provides a
temperature estimation value, corresponding to a temperature of
said display screen, based upon said video signal; an operation
device that determines a temperature difference estimation value
using a reference value corresponding to the temperature of said
outer peripheral portion and said temperature estimation value; and
a control device that controls the luminance of the image based on
the temperature difference estimation value..Iaddend.
Description
TECHNICAL FIELD
The present invention relates to a display device for displaying an
image with luminance corresponding to a video signal inputted from
the exterior and a luminance control method therefore.
BACKGROUND ART
Plasma display devices using PDPs (Plasma Display Panels) have the
advantage that thinning and larger screens are possible. In the
plasma display devices, images are displayed by utilizing light
emission in cases where discharge cells composing pixels are
discharged. As light is thus emitted, heat is generated on a glass
surface composing the PDP, so that the higher the luminance of-an
image. becomes, the larger the amount of heat generation becomes.
Therefore, the temperature of the glass surface is raised. In the
worst case, the glass surface is damaged.
In order to solve the above-mentioned problem, an example of a
conventional display device is a display device disclosed in
JP-A-11-194745. In the display device, the whole surface of a
display screen is divided into a plurality of blocks, temperature
estimated values are calculated with respect to all the blocks, and
the maximum value of the calculated estimated temperatures is
compared with a reference temperature to produce a luminance
correction coefficient. The luminance of the display screen is
controlled by the luminance correction coefficient.
A display on which an image is displayed is generally fixed in its
outer periphery. Damage to the display caused by the rise in the
temperature with the increase in the luminance may occur in the
vicinity of the outer periphery of the display in most cases. That
is, the damage to the display depends on the temperature difference
rather than the maximum temperature. Generally, the temperature
difference between the outer periphery of the display where no heat
is generated and the outer periphery of the display screen of the
display where heat is generated is the largest. The display may be
damaged by thermal stress created by the temperature difference in
many cases.
In the conventional display device, however, only when the maximum
value of the estimated temperatures reaches not less than the
reference temperature, that is, when the temperature of any portion
on the display screen exceeds its certain upper-limit value, the
luminance is controlled.
Therefore, the luminance cannot be always controlled when excessive
thermal stress is exerted on the outer periphery, which is most
easily damaged, of the display, thereby making it impossible to
reliably prevent the display from being damaged.
In the conventional display device, the whole of the display screen
is divided into a plurality of blocks, and the estimated
temperatures are calculated with respect to all the blocks.
Accordingly, operation processing becomes complicated, and long
time is required to perform the operation processing. Particularly
in recent years, it has been desired to make a display image highly
precise. The number of pixels composing the display screen, that
is, the number of discharge cells has tended to be increased. In
this case, the above-mentioned operation processing has
increasingly become complicated, and the processing time is
lengthened.
DISCLOSER OF INVENTION
An object of the present invention is to provide a display device
capable of more reliably preventing a display from being damaged
and a luminance control method therefore.
Another object of the present invention is to provide a display
device capable of more reliably preventing a display from being
damaged in a small amount of operation and a luminance control
method therefore.
A display device according to an aspect of the present invention
comprises a display for displaying an image with luminance
corresponding to a video signal inputted from the exterior; a
temperature estimation circuit for estimating from the video signal
a temperature estimated value corresponding to the temperature of a
display screen of the display; an operation circuit for finding a
temperature difference estimated value using a reference value
corresponding to the temperature of the outer periphery of the
display and the temperature estimated value; and a control circuit
for controlling the luminance of the image displayed on the display
on the basis of the temperature difference estimated value.
In the display device, the temperature estimated value
corresponding to the temperature of the display screen of the
display is estimated from the video signal, and the temperature
difference estimated value is found using the temperature estimated
value and the reference value corresponding to the temperature of
the outer periphery of the display, to control the luminance of the
image displayed on the display on the basis of the temperature
difference estimated value. Generally, the display on which the
image is displayed is fixed in its outer periphery. Accordingly,
damage to the display caused by the rise in the temperature with
the increase in the luminance may occur in the vicinity of the
outer periphery of the display in most cases. Therefore, the
luminance is controlled depending on the temperature difference
estimated value found from the temperature estimated value
corresponding to the temperature of the display screen and the
temperature of the outer periphery of the display, as described
above, so that the luminance can be controlled on the basis of the
temperature difference between the outer periphery of the display
which most greatly affects the damage to the display and the
display screen, thereby making it possible to more reliably prevent
the display from being damaged.
It is preferable that the temperature estimation circuit estimates
the temperature estimated value corresponding to the temperature of
the outer periphery of the display screen of the display.
In this case, the temperature difference estimated value
corresponding to the temperature of the outer periphery of the
display screen of the display is estimated from the video signal,
and the temperature difference estimated value is found using the
temperature estimated value and the reference value corresponding
to the temperature of the outer periphery of the display, to
control the luminance of the image displayed on the display on the
basis of the temperature difference estimated value. The
temperature difference estimated value is found from the
temperature estimated value corresponding to the temperature of the
outer periphery of the display screen and the reference value
corresponding to the temperature of the outer periphery of the
display. Accordingly, the luminance can be controlled on the basis
of the temperature difference between the outer periphery of the
display which greatly affects the damage to the display and the
outer periphery of the display screen closest to the outer
periphery, thereby making it possible to more reliably prevent the
display from being damaged. Further, the temperature estimated
value operated in order to find the temperature difference
estimated value is limited to the temperature estimated value for
the outer periphery of the display screen of the display.
Accordingly, the amount of operation is made smaller than that in a
case where the temperature estimated value on the whole of the
display screen, so that the processing is simplified, and the
processing time is shortened. As a result, it is possible to more
reliably prevent the display from being damaged in a small amount
of operation.
It is preferable that the display comprises first and second boards
between which a plurality of light emitting elements are formed and
to which its outer periphery is fixed, and the outer periphery of
the display includes a portion between the light emitting element
positioned in the outermost periphery out of the plurality of light
emitting elements and a fixed portion of the first and second
boards.
In this case, the reference value corresponds to the temperature of
the portion between the light emitting element positioned in the
outermost periphery and the fixing portion of the first and second
boards. Accordingly, the luminance can be controlled using as a
basis the temperature of the portion most easily damaged, thereby
making it possible to more reliably prevent the display from being
damaged.
It is preferable that the temperature estimation circuit estimates
the temperature estimated value by integrating data relating to the
luminance from the video signal and subtracting the amount of
dissipated heat therefrom, and the operation circuit subtracts the
reference value from the temperature estimated value, to find the
temperature difference estimated value.
In this case, the data relating to the luminance is integrated from
the video signal, and the amount of dissipated heat is subtracted
therefrom, thereby making it possible to find the temperature
estimated value corresponding to the truer temperature.
Consequently, the luminance is controlled on the basis of the
temperature difference estimated value obtained by subtracting the
reference value from the temperature estimated value. Accordingly,
it is possible to control the luminance with higher precision to
more reliably prevent the display from being damaged.
It is preferable that the control circuit lowers the luminance of
the image displayed on the display with the increase in the
temperature difference estimated value.
In this case, the luminance is lowered with the increase in the
temperature difference estimated value, thereby making it possible
to more reliably prevent the display from being damaged.
It is preferable that the control circuit lowers the maximum
luminance of the image displayed on the display with the increase
in the temperature difference estimated value.
In this case, the maximum luminance is lowered with the increase in
the temperature difference estimated value, thereby making it
possible to more reliably prevent the display from being damaged as
well as making it possible to display, when the luminance other
than the maximum luminance is displayed as it is, a good image
corresponding to the luminance of the video signal itself.
It is preferable that the display displays the image with a gray
scale corresponding to the video signal out of a plurality of gray
scales, and the control circuit lowers the luminance of the image
displayed on the display at the same ratio for each of the gray
scales.
In this case, the luminance is lowered at the same ratio for each
gray scale, thereby making it possible to lower the luminance of
the display without giving a visually uncomfortable feeling to a
viewer.
It is preferable that the display displays the image with a gray
scale corresponding to the video signal using a plurality of light
emitting formats which are the same in the total number of gray
scales and differ in the number of light emitting pulses on each of
the gray scales, and the control circuit controls the luminance of
the image displayed on the display using the light emitting format
selected depending on the temperature difference estimated value
out of the plurality of light emitting formats.
In this case, the luminance can be controlled by switching the
plurality of light emitting formats in the order of their
decreasing numbers of light emitting pulses on the same gray scale
with the increase in the temperature difference estimated value,
thereby making it possible to lower the luminance without greatly
changing the total number of gray scales.
It is preferable that the control circuit divides the display
screen of the display into a plurality of blocks, extracts from the
plurality of blocks the peripheral block adjacent to the outer
periphery of the display screen, and lowers the luminance of the
peripheral block.
In this case, the luminance of the peripheral block adjacent to the
outer periphery of the display screen is lowered. Accordingly, the
image in the block inside the display screen can be displayed with
the luminance of the video signal itself, thereby making it
possible to provide a display screen having no visually
uncomfortable feeling by the viewer as well as to more reliably
prevent the outer periphery of the display from being damaged.
It is preferable that the control circuit divides a display screen
of the display into a plurality of blocks, extracts from the
plurality of blocks the peripheral block adjacent to the outer
periphery of the display screen, and makes the luminance of the
peripheral block lower than that of the block inside the display
screen of the display.
In this case, the luminance of the peripheral block is made lower
than that of the block inside the display screen. Accordingly, the
luminance of the display screen is smoothly changed, thereby making
it possible to provide a display screen having no visually
uncomfortable feeling by the viewer as well as to more reliably
prevent the outer periphery of the display from being damaged.
It is preferable that the display device further comprises a block
extraction circuit for dividing the display screen of the display
into a plurality of blocks and extracting from the plurality of
blocks the peripheral blocks adjacent to the outer periphery of the
display screen, the temperature estimation circuit estimates the
temperature estimated values for the peripheral blocks, the
operation circuit finds a peripheral block temperature difference
estimated value from the temperature estimated values estimated for
the peripheral blocks, and the control circuit controls the
luminance for each of the peripheral blocks on the basis of the
peripheral block temperature difference estimated value.
In this case, the display screen is divided into the plurality of
blocks, and the luminance is controlled for each of the peripheral
blocks adjacent to the outer periphery of the display screen.
Accordingly, the luminance can be controlled more finely, thereby
making it possible to provide a display screen having no visually
uncomfortable feeling by the viewer as well as to more reliably
prevent the outer periphery of the display from being damaged.
It is preferable that the control circuit controls the luminance
for each of the peripheral blocks such that the amount of
controlled luminance between the adjacent peripheral blocks is
smoothly changed on the basis of the peripheral block temperature
difference estimated value.
In this case, the amount of controlled luminance between the
adjacent peripheral blocks is smoothly changed. Accordingly, a
display screen having no visually uncomfortable feeling can be
provided for the viewer, and thermal stress created in the outer
periphery of the display is smoothly changed, thereby making it
possible to more reliably prevent the display from being
damaged.
It is preferable that the display device further comprises a block
extraction circuit for dividing the display screen of the display
into a plurality of blocks and extracting from the plurality of
blocks the peripheral blocks adjacent to the outer periphery of the
display screen, the temperature estimation circuit estimates the
temperature estimated values for the peripheral blocks, the
operation circuit finds, out of the temperature estimated values
estimated for the peripheral blocks, peripheral block temperature
difference estimated values for the peripheral blocks, and extracts
from the peripheral block temperature difference estimated values
the maximum peripheral block temperature difference estimated
value, and the control circuit controls the luminance of the image
displayed on the display on the basis of the maximum peripheral
block temperature difference estimated value.
In this case, the luminance is controlled using the maximum
peripheral block temperature difference estimated value
representing the largest temperature difference in the peripheral
blocks, thereby making it possible to more reliably prevent the
display from being damaged. Further, the luminance is controlled by
the maximum peripheral block temperature difference estimated
value, thereby simplifying processing for controlling the
luminance.
It is preferable that the reference value includes a plurality of
reference values which differ depending on the position of the
outer periphery of the display.
In this case, the luminance of the image displayed on the display
can be controlled using the plurality of reference values which
differ depending on the position of the outer periphery of the
display. Accordingly, a high reference value is set in a portion
where the temperature is easily raised, while a low reference value
is set in a portion where the temperature is not easily raised,
thereby making it possible to control the luminance on the basis of
each of the reference values. As a result, the display can be more
reliably prevented from being damaged, and the luminance is not
lowered any more than necessary.
It is preferable that the display device further comprises a
measurement circuit for measuring the temperature of the outer
periphery of the display and outputting to the operation circuit
the reference value corresponding to the measured temperature.
In this case, the temperature of the outer periphery of the display
is directly measured, thereby making it possible to control the
luminance on the basis of the reference value corresponding to the
temperature. Even when the reference value is changed by the
variation in outside air temperature, for example, it is possible
to reliably prevent the display from being damaged.
A luminance control method for a display device according to
another aspect of the present invention is a luminance control
method for a display device comprising a display for displaying an
image with luminance corresponding to a video signal inputted from
the exterior, characterized by comprising the steps of estimating
from the video signal a temperature estimated value corresponding
to the temperature of a display screen of the display; finding a
temperature difference estimated value using a reference value
corresponding to the temperature of the outer periphery of the
display and the temperature estimated value; and controlling the
luminance of the image displayed on the display on the basis of the
temperature difference estimated value.
In the luminance control method for the display device, the
temperature estimated value corresponding to the temperature of the
display screen of the display is estimated from the video signal,
and the temperature difference estimated value is found using the
temperature estimated value and the reference value corresponding
to the temperature of the outer periphery of the display, to
control the luminance of the image displayed on the display on the
basis of the temperature difference estimated value. Generally, the
display on which the image is displayed is fixed in its outer
periphery. The damage to the display caused by the increase in the
luminance may occur in the vicinity of the outer periphery of the
display in most cases. Consequently, the luminance is controlled
depending on the temperature difference estimated value found from
the temperature estimated value corresponding to the temperature of
the display screen and the reference value corresponding to the
temperature of the outer periphery of the display, thereby making
it possible to control the luminance on the basis of the
temperature difference between the outer periphery of the display
which most greatly affects the damage to the display and the
display screen and to more reliably prevent the display from being
damaged.
It is preferable that the temperature estimating step comprises the
step of estimating the temperature estimated value corresponding to
the temperature of the outer periphery of the display screen of the
display.
In this case, the temperature estimated value corresponding to the
temperature of the outer periphery of the display screen of the
display is estimated from the video signal, and the temperature
different estimated value is found using the temperature estimated
value and the reference value corresponding to the temperature of
the outer periphery of the display, to control the luminance of the
image displayed on the display on the basis of the temperature
difference estimated value. The temperature difference estimated
value is found from the temperature estimated value corresponding
to the temperature of the outer periphery of the display screen and
the reference value corresponding to the temperature of the outer
periphery of the display. Accordingly, the luminance can be
controlled on the basis of the temperature difference between the
outer periphery of the display which most greatly affects the
damage to the display and the outer periphery of the display screen
closest to the outer periphery of the display, thereby making it
possible to more reliably prevent the display from being damaged.
Further, the temperature estimated value operated in order to find
the temperature difference estimated value is limited to the
temperature estimated value for the outer periphery of the display
screen of the display. Accordingly, the amount of operation is made
smaller than that in a case where the temperature estimated value
on the whole of the display screen is operated, so that the
processing is simplified, and the processing time is shortened. As
a result, it is possible to more reliably prevent the display from
being damaged in a small amount of operation.
It is preferable that the display displays the image on a gray
scale corresponding to the video signal using a plurality of light
emitting formats which are the same in the total number of gray
scales and differ in the number of light emitting pulses on each of
the gray scales, and the controlling step comprises the step of
controlling the luminance of the image displayed on the display
using the light emitting format selected depending on the
temperature difference estimated value out of the plurality of
light emitting formats.
In this case, the luminance can be controlled by switching the
plurality of light emitting formats in the order of their
decreasing numbers of light emitting pulses on the same gray scale
with the increase in the temperature difference estimated value,
thereby making it possible to lower the luminance without greatly
changing the total number of gray scales.
It is preferable that the controlling step comprises the step of
dividing the display screen of the display into a plurality of
blocks, extracting from the plurality of blocks the peripheral
blocks adjacent to the outer periphery of the display screen, and
lowering the luminance of the peripheral blocks.
In this case, the luminance of the peripheral blocks adjacent to
the outer periphery of the display screen is lowered. Accordingly,
the image in the block inside the display screen can be displayed
with the luminance of the video signal itself, thereby making it
possible to provide a display screen having no visually
uncomfortable feeling by the viewer as well as to more reliably
prevent the outer periphery of the display from being damaged.
It is preferable that the luminance control method for the display
device further comprises the step of dividing the display screen of
the display into a plurality of blocks and extracting from the
plurality of blocks the peripheral blocks adjacent to the outer
periphery of the display screen, the temperature estimating step
comprises the step of estimating the temperature estimated values
for the peripheral blocks, the temperature difference estimated
value operating step comprises the step of finding a peripheral
block temperature difference estimated value from the temperature
estimated values estimated for the peripheral blocks, and the
controlling step comprises the step of controlling the luminance
for each of the peripheral blocks on the basis of the peripheral
block temperature difference estimated value.
In this case, the display screen is divided into the plurality of
blocks, and the luminance is controlled for each of the peripheral
blocks adjacent to the outer periphery of the display screen.
Accordingly, the luminance can be controlled more finely, thereby
making it possible to provide a display screen having no visually
uncomfortable feeling by the viewer as well as to more reliably
prevent the outer periphery of the display from being damaged.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a block diagram showing the configuration of a plasma
display device according to a first embodiment of the present
invention.
FIG. 2 is a block diagram showing the configuration of a
temperature difference estimator shown in FIG. 1.
FIG. 3 is a block diagram showing the configuration of a brightness
controller shown in FIG. 1.
FIG. 4 is a block diagram showing the configuration of a display
shown in FIG. 1.
FIG. 5 is a schematic view showing the configuration of a PDP shown
in FIG. 4.
FIG. 6 is a diagram showing sub-fields used for each gray scale
level in a case where an image is displayed on 256 gray scales.
FIG. 7 is a diagram showing the respective numbers of light
emitting pulses in each sub-field in different light emitting
formats.
FIG. 8 is a diagram showing the relationship between a temperature
difference estimated value and a multiplication factor in a case
where light emitting formats A to E shown in FIG. 7 are used.
FIG. 9 is a diagram showing the relationship between a temperature
difference estimated value and luminance after control in a case
where the temperature difference estimated value and the
multiplication factor shown in FIG. 8 are used.
FIG. 10 is a diagram showing the relationship between a temperature
difference estimated value and a multiplication factor in a case
where a light emitting format A shown in FIG. 7 is used.
FIG. 11 is a diagram for explaining a second luminance control
method for the plasma display device shown in FIG. 1.
FIG. 12 is a diagram for explaining a third luminance control
method for the plasma display device shown in FIG. 1.
FIG. 13 is a block diagram showing the configuration of a plasma
display device according to a second embodiment of the present
invention.
FIG. 14 is a block diagram showing the configuration of a
temperature difference estimator shown in FIG. 13.
FIG. 15 is a diagram showing an example of a temperature estimated
value and a peripheral block temperature difference estimated value
which are estimated for each peripheral block.
FIG. 16 is a diagram showing an example of a peripheral block
temperature difference estimated value and a multiplication factor
by a first luminance control method for the plasma display device
shown in FIG. 13.
FIG. 17 is a diagram showing an example of a peripheral block
temperature difference estimated value, a peripheral lock
temperature difference estimated value after filtering processing,
and a multiplication factor by a second luminance control method
for the plasma display device shown in FIG. 3.
FIG. 18 is a block diagram showing the configuration of plasma
display device according to a third embodiment of the present
invention.
FIG. 19 is a block diagram showing the configuration of a
temperature difference estimator shown in FIG. 18.
FIG. 20 is a diagram showing an example of a temperature difference
estimated value, a peripheral block temperature difference
estimated value, and a maximum peripheral block temperature
difference estimated value which are estimated for each peripheral
block.
FIG. 21 is a block diagram showing the configuration of a plasma
display device according to a fourth embodiment of the present
invention.
BEST MODE FOR CARRYING OUT THE INVENTION
An AC-type plasma display device will be described as an example of
a display device according to the present invention. A display
device to which the present invention is applied is not
particularly limited to the AC-type plasma display device. The
present invention is similarly applicable to another display
device, provided that the temperature of a display screen is
changed by a change in luminance.
A plasma display device according to a first embodiment of the
present invention will be first described. FIG. 1 is a block
diagram showing the configuration of the plasma display device
according to the first embodiment of the present invention.
The plasma display device shown in FIG. 1 comprises a display 1, a
brightness controller 2, a controller 3, a temperature difference
estimator 4, and a panel periphery temperature setter 5.
A video signal VS is inputted to the brightness controller 2 and
the temperature difference estimator 4. The panel periphery
temperature setter 5 sets a reference value To representing the
temperature of the panel outer periphery of the display 1, and
outputs the reference value To to the temperature difference
estimator 4. The temperature difference estimator 4 calculates a
temperature difference estimated value Td representing the
difference between the temperature of the panel outer periphery of
the display 1 and the temperature of the display screen of the
display 1 using the video signal VS and the reference value To, and
outputs the temperature difference estimated value Td to the
controller 3.
The controller 3 outputs to the brightness controller 2 a
brightness control signal LC for controlling the luminance of the
display screen of the display 1 depending on the temperature
difference estimated value Td. The brightness controller 2 outputs
to the display 1 a data driver driving control signal DS, a scan
driver driving control signal CS, and a sustain driver driving
control signal US for displaying an image with luminance
corresponding to the brightness control signal LC.
FIG. 2 is a block diagram showing the configuration of the
temperature difference estimator 4 shown in FIG. 1. As shown in
FIG. 2, the temperature difference estimator 4 comprises a
periphery adjacent portion separator 41, an integration circuit 42,
a dissipated heat subtraction circuit 43, and a subtracter 44.
The periphery adjacent portion separator 41 receives the video
signal VS, separates from the video signal VS a portion of a
periphery adjacent portion adjacent to the outer periphery of the
display screen of the display 1 from the video signal VS and
outputs the separated portion to the integration circuit 42. The
video signal VS includes not only an inherent video signal but also
a vertical synchronizing signal, a horizontal synchronizing signal,
and so forth. The periphery adjacent portion is separated using the
horizontal synchronizing signal, the vertical synchronizing signal,
and so forth.
The integration circuit 42 integrates data relating to luminance
from the video signal for the periphery adjacent portion separated
by the periphery adjacent portion separator 41, for example, a
luminance signal for the periphery adjacent portion, and outputs
the integrated luminance signal to the dissipated heat subtraction
circuit 43.
The dissipated heat subtraction circuit 43 subtracts the amount of
dissipated heat from the integrated luminance signal for the
periphery adjacent portion to calculate a temperature estimated
value Te representing the temperature of the periphery adjacent
portion, and outputs the temperature estimated value Te to the
subtracter 44.
The subtracter 44 subtracts the reference value To for the panel
outer periphery from the temperature estimated value Te for the
periphery adjacent portion to find a temperature difference
estimated value Td for the outer periphery of the display screen,
and outputs the temperature difference estimated value Td to the
controller 3.
The controller 3 selects, out of a plurality of light emitting
formats, the corresponding light emitting format depending on the
temperature difference estimated value Td found by the processing,
generates a brightness control signal LC including a light emitting
pulse control signal EC for designating the selected light emitting
format and a multiplication factor k in the selected light emitting
format, and outputs the generated brightness control signal LC to
the brightness controller 2.
FIG. 3 is a block diagram showing the configuration of the
brightness controller 2 shown in FIG. 1. As shown in FIG. 3, the
brightness controller 2 comprises a multiplication circuit 21, a
video signal/sub-field corresponder 22, and a sub-field pulse
generator 23.
The multiplication circuit 21 multiplies the video signal VS by the
multiplication factor k included in the brightness control signal
LC, and outputs to the video signal/sub-field corresponder 22 a
video signal whose luminance has been controlled by the
multiplication factor k.
The video signal/sub-field corresponder 22 divides one field into a
plurality of sub-fields to perform display.
Accordingly, it generates from a video signal corresponding to one
field image data for each sub-field in the light emitting format
designated from the plurality of light emitting formats in response
to the light emitting pulse control signal EC included in the
brightness control signal LC, and outputs a data driver driving
control signal DC corresponding to the image data for each
sub-field to the display 1.
The sub-field pulse generator 23 outputs to the display 1 the scan
driver driving control signal CS and the sustain driver driving
control signal US which correspond to each sub-field in the light
emitting format designated from the plurality of light emitting
formats in response to the light emitting pulse control signal EC
included in the brightness control signal LC.
FIG. 4 is a block diagram showing the configuration of the display
1 shown in FIG. 1. The display shown in FIG. 1 comprises a PDP
(Plasma Display Panel) 11, a data driver 12, a scan driver 13, and
a sustain driver 14.
The data driver 12 is connected to a plurality of address
electrodes (data electrodes) AD in the PDP 11. The scan driver 13
contains driving circuits respectively provided for scan electrodes
SC in the PDP 11, and each of the driving circuits is connected to
the corresponding scan electrode SC. The sustain driver 14 is
together connected to a plurality of sustain electrodes SU in the
PDP 11.
The data driver 12 applies a write pulse to the corresponding
address electrode AD in the PDP 11 during a write time period in
accordance with the data driver driving control signal DS. On the
other hand, the scan driver 13 successively applies the write
pulses to the plurality of scan electrodes SC in the PDP 11 while
shifting a shift pulse in the vertical scanning direction during
the write time period in accordance with the scan driver driving
control signal CS. Consequently, address discharges are induced in
the corresponding discharge cell, and the discharge cell
corresponding to the video signal VS is selected.
The scan driver 13 applies periodical sustain pulses to the
plurality of scan electrodes SC in the PDP 11 during a sustain time
period in accordance with the scan driver driving control signal
CS. On the other hand, the sustain driver 14 simultaneously applies
sustain pulses which are shifted in phase by 180.degree. from the
sustain pulses applied to the scan electrodes SC in the sustain
time period in accordance with the sustain driver driving control
signal US. Consequently, sustain discharges are induced in the
discharge cell selected in an address time period, and an image is
displayed on the display screen with luminance corresponding to the
video signal VS.
FIG. 5 is a schematic view showing the configuration of the PDP 11
shown in FIG. 4. As shown in FIG. 5, the PDP 11 comprises a
plurality of address electrodes AD, a plurality of scan electrodes
SC, a plurality of sustain electrodes SU, a surface glass board FP,
a reverse glass board BP, and a barrier wall WA.
The plurality of address electrodes AD are arranged in the vertical
direction on the screen, and the plurality of scan electrodes SC
and the plurality of sustain electrodes SU are arranged in the
horizontal direction on the screen. Further, the sustain electrodes
SU are together connected. A discharge cell CE is formed at each of
the intersections of the address electrodes AD, the scan electrodes
SC, and the sustain electrodes SU. Each of the discharge cells CE
composes a pixel on the screen.
Furthermore, the scan electrodes SC and the sustain electrodes SU
are formed in the horizontal direction on the screen such that they
are paired on the surface glass board FP, and are covered with a
transparent dielectric layer and a protective layer. On the other
hand, the address electrodes AD are formed in the vertical
direction on the screen on the reverse glass board BP opposite to
the surface glass board FP, a transparent dielectric layer is
formed thereon, and a fluorescent member is further applied
thereon. The barrier wall WA is provided between the address
electrodes AD, so that the adjacent discharge cells CE are
separated from each other. When color display is performed, the
address electrodes AD are provided every R, G; and B, and the
barrier wall WA is provided between the address electrodes AD.
The surface glass board FP and the reverse glass board BP are fixed
with their outer peripheries joined to each other by a sealing
glass SG. When the temperatures of the surface glass board FP and
the reverse glass board BP are raised by causing the display cells
CE to emit light, cracks occur in the vicinity of the sealing glass
SG for the surface glass board FP and the reverse glass board BP.
Consequently, the PDP 11 may be damaged in many cases. In the
present embodiment, the luminance of the PDP 11 is controlled on
the basis of the temperature difference in the portion most easily
damaged. Therefore, the temperature difference estimated value Td
is found in the following manner.
A portion, including at least the discharge cells CE positioned in
the outermost periphery (for example, a square frame portion
indicated by hatching), of the display screen of the PDP 11, that
is, a portion where the discharge cells CE are formed is taken as a
periphery adjacent portion NE, to separate a video signal in the
region by the periphery adjacent portion separator 41 in the
temperature difference estimator 4. The separated video signal is
integrated, for example, by the integration circuit 42 and the
dissipated heat subtraction circuit 43, to find a temperature
estimated value Te representing the temperature of the periphery
adjacent portion NE.
On the other hand, the panel periphery temperature setter 5 takes a
portion of the sealing glass SG for the surface glass board FP and
the reverse glass board BP and a portion between the discharge cell
CE positioned in the outermost periphery and the sealing glass SG
as the panel outer periphery, and sets the temperature of the
portion as a reference value To. Consequently, the reference value
To for the panel outer periphery is subtracted from the temperature
estimated value Te for the periphery adjacent portion NE, thereby
operating the temperature difference estimated value Td for the
outer periphery of the display screen. Consequently, the luminance
is controlled, as described later, using the temperature difference
estimated value Td representing the temperature difference in the
portion most easily damaged, thereby more reliably preventing the
PDP 11 form being damaged.
In the present embodiment, the PDP 11 corresponds to a display, the
temperature difference estimator 4 corresponds to a temperature
estimation circuit and an operation circuit, and the brightness
controller 2, the controller 3, the data driver 12, the scan driver
13, and the sustain driver 14 correspond to a control circuit.
Further, the periphery adjacent portion separator 41, the
integration circuit 42, and the dissipated heat subtraction circuit
43 correspond to a temperature estimation circuit, and the
subtracter 44 corresponds to an operation circuit.
Description is now made of a gray scale display method using five
types of light emitting formats in which the total number of gray
scales is 256, and one field is divided into eight sub-fields to
perform display as an example of a gray scale display method for
the display device configured as described above. The gray scale
display method to which the present invention is applied is not
particularly limited to the following example. Another gray scale
display method may be used.
FIG. 6 is a diagram showing sub-fields where sustain discharges
should be induced when the display screen is displayed at each gray
scale level in a case where the total number of gray scales is 256.
In FIG. 6, the sub-fields SF1 to SF8 are successively respectively
weighted with brightness values 1, 2, 4, 8, 16, 32, 64, and 128,
for example. Each of the weights is a value proportional to the
luminance of the display screen, for example, the number of times
of light emission in each of the discharge cells.
In FIG. 6, the sub-fields SF1 to SF8 used for causing the discharge
cell to emit light at each gray scale level are indicated by o. In
order to cause the discharge cell to emit light at a gray scale
level 1, the sub-field SF1 (a weight 1) may be used. In order to
cause the discharge cell to emit light at a gray scale level 3, the
sub-field SF1 and the sub-field SF2 (a weight 2) may be used, and a
corresponding column in each of the sub-fields is assigned o. If
the sub-fields are combined with each other to cause the discharge
cell to emit light in a number of times of light emission
corresponding to the weight, gray scale display can be performed at
each of the gray scale levels 0 to 255. The number of sub-fields
obtained by the division, the weights, and so forth are not
particularly limited to those in the abovementioned example, and
various modifications are possible.
Description is now made of five types of light emitting formats in
which the total number of gray scales is 256 as an example of a
light emitting format using the sub-fields SF1 to SF8 which are
weighted as described above.
FIG. 7 is a diagram showing the number of light emitting pulses in
each of the sub-fields SF1 to SF8 in each of the five types of
light emitting formats A to E. Each of the light emitting formats A
to E is determined by the controller 2 depending on the temperature
estimated value Td, as described later, and is specified by the
light emitting pulse control signal EC.
In the light emitting format A, the total number of light emitting
pulses is 1275, five light emitting pulses are assigned to the
sub-field SF1, 10 light emitting pulses are assigned to the
sub-field SF2, and 20, 40, 80, 160, 320, and 640 light emitting
pulses are similarly assigned, respectively, to the sub-fields SF3
to SF8.
The total number of light emitting pulses is 1020 in the light
emitting format B, the total number of light emitting pulses is 765
in the light emitting format C, the total number of light emitting
pulses is 510 in the light emitting format D, and the total number
of light emitting pulses in the light emitting format E is 255. The
number of light emitting pulses, as shown, is assigned to each of
the sub-fields SF1 to SF8.
When the sub-fields SF1 to SF8 are combined to perform display on
256 gray scales, therefore, the light emitting formats A to E
differ in the number of light emitting pulses and luminance even at
the same gray scale level. That is, when the luminance in the light
emitting format E is used as a basis (once), the luminance in the
light emitting format D is twice that in the light emitting format
E, the luminance in the light emitting format C is three times that
in the light emitting format E, the luminance in the light emitting
format B is four times that in the light emitting format E, and the
luminance in the light emitting format A is five times that in the
light emitting format E. Consequently, the light emitting formats
are successively switched from A to E, therefore, the luminance of
the display screen can be lowered without significantly changing
the total number of gray scales.
Description is now made of the relationship between a temperature
difference estimated value Td and a multiplication factor k in a
case where the light emitting formats A to E are combined with each
other to induce sustain discharges. FIG. 8 is a diagram showing the
relationship between a temperature difference estimated value Td
and a multiplication factor k in a case where the light emitting
formats A to E are combined with each other to induce sustain
discharges. The relationship between the temperature difference
estimated value Td and the multiplication factor k shown in FIG. 8
is previously stored in the controller 3. The light emitting format
and the multiplication factor k which correspond to the temperature
difference estimated value Td estimated by the temperature
difference estimator 4 are specified by the controller 3.
As shown in FIG. 8, in the light emitting format A, as the
temperature difference estimated value Td increases, the
multiplication f actor k linearly decreases from 1.0 to 0.8. Then,
in the light emitting format B, as the temperature difference
estimated value Td increases, the multiplication factor k decreases
from 1.0 to 0.75. Then, in the light emitting format C, as the
temperature difference estimated value Td increases, the
multiplication factor k decreases from 1.0 to 0.67. Then, in the
light emitting format D, as the temperature difference estimated
value Td increases, the multiplication factor k decreases from 1.0
to 0.5. Finally, in the light emitting format E, as the temperature
difference estimated value Td increases, the multiplication factor
k decreases from 1.0.
From the following reason, the multiplication factor is returned to
1.0 when the light emitting format is switched after decreasing
from 1.0. That is, the total number of light emitting pulses in the
light emitting format A is 1275, and the total number of light
emitting pulses in the light emitting format B is 1020.
Accordingly, the ratio of the numbers of pulses is 0.8. When the
light emitting format is switched from A to B, therefore, the
multiplication factor k is switched from 0.8 to 1.0, thereby making
it possible to reduce the number of light emitting pulses at a
predetermined ratio depending on the temperature difference
estimated value Td before and after the switching and to linearly
control the luminance of the display screen. The same is true even
at the time of later switching the light emitting format.
The multiplication factor k is thus switched depending on the total
number of light emitting pulses at the time of switching the light
emitting format, thereby making it possible to linearly control the
luminance of the display screen depending on the temperature
difference estimated value Td even when the image is displayed
using the different light emitting format as well as to lower the
luminance without extremely reducing the total number of gray
scales.
When the video signal VS is multiplexed by the multiplication
factor k, to display the image using the video signal, the
temperature difference estimated value Td increases, and the
luminance after the control linearly decreases, as shown in FIG. 9,
thereby making it possible to lower the luminance of the display
screen depending on the temperature difference estimated value Td.
In FIG. 9, the luminance in a case where the luminance is not
decreased, that is, the temperature difference estimated value Td
is zero is 5 (a relative value).
The light emitting format is not particularly limited to the
above-mentioned example. The sustain discharges may be induced
using only the light emitting format A out of the light emitting
formats A to E. FIG. 10 is a diagram showing the relationship
between the temperature difference estimated value Td and the
multiplication factor k in a case where the light emitting format A
is used. When the temperature difference estimated value Td is
zero, that is, the temperature is not raised, as shown in FIG. 10,
the multiplication factor k is outputted as 1.0. As the temperature
difference estimated value Td increases, the multiplication factor
k linearly decreases. Consequently, the video signal VS is
multiplexed by the multiplication factor k by the multiplication
circuit 21, thereby making it possible to lower the luminance of
the display screen depending on the temperature difference
estimated value Td, as in a case shown in FIG. 9.
Description is now made of a first luminance control method for the
plasma display device configured as described above.
First in the temperature difference estimator 4, a video signal for
the periphery adjacent portion is separated from a video signal VS
by the periphery adjacent portion separator 41, a luminance signal
in the video signal for the periphery adjacent portion is
integrated by the integration circuit 42, and the amount of
dissipated heat is subtracted by the dissipated heat subtraction
circuit 43, to calculate a temperature estimated value Te for the
periphery adjacent portion. A reference value To for the panel
outer periphery set by the panel periphery temperature setter 5 is
subtracted from the temperature estimated value Te for the
periphery adjacent portion by the subtracter 44, so that a
temperature difference estimated value Td for the periphery of the
display screen is calculated.
As shown in FIG. 8, a light emitting format and a multiplication
factor k which correspond to the temperature difference estimated
value Td are then determined by the controller 3, so that a light
emitting pulse control signal EC corresponding to the determined
light emitting format and a brightness control signal LC including
the determined multiplication factor k are generated.
Then in the brightness controller 2, the video signal VS is
multiplied by the multiplication factor k included in the
brightness control signal LC by the multiplication circuit 21, so
that a video signal whose luminance has been controlled is
generated depending on the multiplication factor k. Image data for
each sub-field in the light emitting format corresponding to the
light emitting pulse control signal EC included in the brightness
control signal LC is then generated from the video signal
corresponding to one field whose luminance has been controlled by
the video signal/sub-field corresponder 22, and a data driver
driving control signal DS corresponding to the image data is
outputted. Further, a scan driver driving control signal CS and a
sustain driver driving control signal US which correspond to each
sub-field in the light emitting format corresponding to the light
emitting pulse control signal EC are generated by the sub-field
pulse generator 23.
Finally, in the display 1, address discharges in the corresponding
discharge cell are induced in response to the data driver driving
control signal DS and the scan driver driving control signal CS by
the data driver 12 and the scan driver 13, and sustain discharges
are then induced in the discharge cell in which the address
discharges have been induced in response to the scan driver driving
control signal CS and the sustain driver driving control signal US
by the scan driver 13 and the sustain driver 14. Accordingly, an
image is displayed on the display screen with the luminance
controlled depending on the multiplication factor k. The larger the
temperature difference estimated value Td becomes, the lower the
luminance of the display screen becomes.
As described in the foregoing, in the luminance control method, the
temperature estimated value Te corresponding to the temperature of
the periphery adjacent portion of the display screen of the PDP 11
is estimated from the video signal VS, the temperature difference
estimated value Td is found using the temperature estimated value
Te and the reference value To corresponding to the temperature of
the panel outer periphery, the light emitting format and the
multiplication factor k which correspond to the temperature
difference estimated value Td are determined, and the luminance of
the display screen of the PDP 11 is controlled by the light
emitting format and the multiplication factor k which have been
determined. Consequently, the luminance can be controlled on the
basis of the temperature difference between the panel outer
periphery which greatly affects the damage to the PDP 11 and the
periphery adjacent portion closest to the panel outer periphery,
thereby making it possible to more reliably prevent the PDP 11 from
being damaged. Further, only the temperature estimated value Td for
the periphery adjacent portion is operated, so that the amount of
operation is reduced, thereby making it possible to simplify the
processing as well as to shorten the processing time.
Description is now made of a second luminance control method for
the plasma display device. The second luminance control method is a
method of dividing the display screen into a plurality of blocks
and controlling the luminance of the peripheral block adjacent to
the outer periphery of the display screen out of the blocks
obtained by the division. The control method is carried out by the
controller 3 outputting a multiplication factor k corresponding to
a temperature difference estimated value Td when a video signal VS
corresponding to the peripheral block is inputted to the
multiplication circuit 21, outputting one as the multiplication
factor k when the video signal VS corresponding to the inner block
other than the peripheral block is inputted to the multiplication
circuit 21, and multiplying the video signal VS by the
multiplication factors k by the multiplication circuit 21. In this
case, a vertical synchronizing signal and a horizontal
synchronizing signal, for example, are inputted to the controller 3
through the temperature difference estimator 4, and the display
screen is divided using the horizontal synchronizing signal and the
vertical synchronizing signal, for example, to specify the
peripheral block.
FIG. 11 is a diagram showing an example of a multiplication factor
k for each block in a case where the luminance of the peripheral
block is controlled. In the following, description is made of a
case where the display screen is divided into a total of 25 blocks,
that is, five blocks in the longitudinal direction and five blocks
in the transverse direction. However, the number of divisions of
the display screen is not particularly limited to that in this
example. The number can be suitably determined depending on the
number of pixels composing the display screen, and the processing
capabilities of the temperature difference estimator 4, the
controller 3, and so forth, for example. In FIG. 11, a discharge
cell in the outermost periphery is positioned in the outermost
periphery of each peripheral block, and an outer frame indicates
the outer periphery of the PDP 11.
In the example shown in FIG. 11, the multiplication factor k for
the peripheral blocks (blocks indicated by hatching) is set to 0.5,
and the multiplication factor k for the outer inner blocks is set
to one. In this case, the multiplication factor k is decreased only
in a portion of the peripheral block most easily damaged, and the
luminance of this portion is reduced. Consequently, the PDP 11 can
be more reliably prevented from being damaged without lowering the
luminance of the inside of the display screen.
Description is now made of a third luminance control method for the
plasma display device. The third luminance control method is a
method of controlling the luminance of each of blocks such that the
luminance of the peripheral block is made lower than that of the
inner block. The control method is carried out by the controller 3
outputting a multiplication factor k corresponding to a temperature
difference estimated value Td when a video signal VS corresponding
to the peripheral block is inputted to the multiplication circuit
21, increasing the multiplication factor k depending on the
position of each of the blocks such that the multiplication factor
for the block at the center is one when the video signal VS
corresponding to the inner block other than the peripheral block is
inputted to the multiplication circuit 21, and multiplying the
video signal VS by the multiplication factor k by the
multiplication circuit 21.
FIG. 12 is a diagram showing an example of the multiplication
factor k for each block in a case where the luminance of the blocks
is controlled such that the luminance of the peripheral blocks is
made lower than that of the inner blocks. In the example shown in
FIG. 12, the multiplication factor k for the peripheral blocks is
set to 0.5, the multiplication factor k for the inner blocks is set
to 0.75, and the multiplication factor k for the block at the
center is set to one. In this case, the luminance of a portion of
the peripheral block most easily damaged is most greatly reduced,
thereby making it possible to more reliably prevent the PDP 11 from
being damaged. Since the multiplication factor k is gradually
decreased toward the outer periphery of the PDP 11, the change in
the luminance by the change in the multiplication factor k is
difficult to visually know, thereby making it possible to prevent
the image quality from being degraded. The amount of change of the
multiplication factor k depending on the position of the block is
not particularly limited to that in the above-mentioned example.
Various modifications are possible. For example, the amount of
change on the side of the outer periphery is made larger.
Description is now made of a plasma display device according to a
second embodiment of the present invention. FIG. 13 is a block
diagram showing the configuration of the plasma display device
according to the second embodiment of the present invention.
The plasma display device shown in FIG. 13 divides a display screen
of a display 1 into a plurality of blocks, finds a peripheral block
temperature difference estimated value Tbd for each peripheral
block adjacent to the outer periphery of the display screen out of
the blocks obtained by the division, and controls luminance using
the peripheral block temperature difference estimated value Tbd.
Consequently, the plasma display device shown in FIG. 13 is the
same as the plasma display device shown in FIG. 1 except that the
temperature difference estimator 4 is changed into a temperature
difference estimator 4A for estimating the peripheral block
temperature difference estimated value Tbd for each peripheral
block. Accordingly, the same portions are assigned the same
reference numerals and hence, the description thereof is not
repeated. Only the temperature difference estimator 4A obtained by
the change will be described in detail.
FIG. 14 is a block diagram showing the configuration of the
temperature difference estimator 4A shown in FIG. 13. The
temperature difference estimator 4A shown in FIG. 14 is the same as
the temperature difference estimator 4 shown in FIG. 2 except that
a block separator 45 is added between a periphery adjacent portion
separator 41 and an integration circuit 42. Accordingly, the same
portions are assigned the same reference numerals and hence, the
description thereof is not repeated.
As shown in FIG. 14, the block separator 45 is connected to the
periphery adjacent portion separator 41, and receives a video
signal for a periphery adjacent portion which is outputted from the
periphery adjacent portion separator 41, separates the video signal
for each peripheral block adjacent to the outer periphery of the
display screen, and outputs the divided video signal to the
integration circuit 42. In this case, a vertical synchronizing
signal and a horizontal synchronizing signal, for example, included
in the video signal VS are inputted to the block separator 45, so
that the peripheral block is extracted using the horizontal
synchronizing signal and the vertical synchronizing signal, for
example. In a stage succeeding the integration circuit 42, each
processing is performed, as in the first embodiment, for each
peripheral block. Finally, the peripheral block temperature
difference estimated value Tbd is outputted for each peripheral
block from a subtracter 44.
FIG. 15 is a diagram showing an example of a temperature estimated
value Tb and a peripheral block temperature difference estimated
value Tbd which are estimated for each peripheral block. Although
in the following, description is made of a case where the display
screen is divided into five blocks in the longitudinal direction
and five blocks in the transverse direction, and the block adjacent
to the outer periphery of the display screen out of the blocks
obtained by the division is taken as a peripheral block, the number
of divisions of the display screen is not particularly limited to
that in this example. The number can be suitably determined
depending on the number of pixels composing the display screen, and
the processing capabilities of the temperature difference estimator
4A, the controller 3, and so forth, for example. In FIG. 15, a
discharge cell in the outermost periphery is positioned in the
outermost periphery of the peripheral block, and an outer frame
indicates the outer periphery of a PDP 11.
As shown in FIG. 15(a), the temperature estimated value Tb is
determined for each peripheral block. For example, the temperature
estimated value Tb for the peripheral block in the upper left of
the display screen is 17, the temperature estimated value Tb for
the peripheral block adjacent thereto on the right side is 18, and
the temperature estimated value Tb for the peripheral block
adjacent thereto on the right side is 20. The temperature estimated
value Tb is thus estimated for each peripheral block.
A reference value To is subtracted from each of the temperature
estimated values Tb shown in FIG. 15(a). In this example, the
reference value To for the peripheral blocks included in two rows
in an upper part UR is set to 10, and the reference value To for
the peripheral blocks included in three rows in a lower part DR is
set to five. Consequently, the peripheral block temperature
difference estimated value Tbd for each of the peripheral blocks
from which each of the reference values has been subtracted is a
value shown in FIG. 15(b). A multiplication factor k is determined,
as in FIG. 8, for each of the peripheral blocks using the value,
and the luminance of the peripheral block is controlled depending
on the multiplication factor k.
Generally in the PDP 11, an address electrode AD is wired to its
upper part, as shown in FIG. 5. Accordingly, a vent for cooling,
for example, is provided in its lower part. The temperature of the
upper part tends to be raised more easily, as compared with the
temperature of the lower part. Consequently, a high reference value
is set with respect to the upper part UR in the PDP 11, and a lower
reference value is set in the lower part DR, as compared with that
in the upper part UR, thereby making it possible to calculate a
temperature difference estimated value closer to thermal stress
actually created in the panel outer periphery of the PDP 11. As a
result, the PDP 11 can be more reliably prevented from being
damaged, and the luminance is not lowered any more than necessary.
A method of controlling luminance using a plurality of reference
values which differ depending on the position of the panel outer
periphery of the PDP 11, as described above, is also applicable to
other embodiments.
The controller 3 uses the peripheral block temperature difference
estimated value Tbd for each peripheral block found in the
above-mentioned manner, to output a brightness control signal LC to
a brightness controller 2 such that luminance is controlled for
each peripheral block. The brightness controller 2 outputs to the
display 1 an address driver driving control signal AD, a scan
driver driving control signal CS, and a sustain driver driving
control signal US for controlling the luminance for each peripheral
block in response to a brightness control signal LC. In the display
1, the luminance is controlled for each peripheral block in
response to each of the inputted driving control signals by each
luminance control method described below.
The present embodiment is the same as the first embodiment except
that the temperature difference estimator 4A corresponds to a
temperature estimation circuit and an operation circuit, and the
block separator 45 corresponds to a block extraction circuit.
A first luminance control method for the plasma display device
configured as described above will be described. The first
luminance control method is a method of estimating a temperature
estimated value Tb for each peripheral block, subtracting a
reference value To from the temperature estimated value Tb for the
peripheral block to find a peripheral block temperature difference
estimated value Tbd, and controlling luminance depending on the
peripheral block temperature difference estimated value Tbd for the
peripheral block. Also in the control method, a multiplication
factor k corresponding to the peripheral block temperature
difference estimated value Tbd for the peripheral block is
outputted when a video signal VS corresponding to the peripheral
block separated by the block separator 45 is inputted to a
multiplication circuit 21, one is outputted as the multiplication
factor k when the video signal VS corresponding to the inner block
other than the peripheral block is inputted to the multiplication
circuit 21, and the video signal VS is multiplied by the
multiplication factors k by the multiplication circuit 21.
FIG. 16 is a diagram showing an example of a peripheral block
temperature difference estimated value Tbd and a multiplication
factor for each peripheral block in a case where luminance is
controlled for the peripheral block by the first luminance control
method.
First, as shown in FIG. 16(a), it is assumed that a peripheral
block temperature difference estimated value Tbd is estimated for
each peripheral block. That is, it is assumed that the peripheral
block temperature difference estimated value Tbd for the peripheral
blocks positioned at the respective centers of the upper side, the
lower side, the left side, and the right side of the display screen
is 20, and the peripheral block temperature difference estimated
value Tbd for the other peripheral blocks is zero. In this case, a
multiplication factor k for the peripheral block is as shown in
FIG. 16(b). That is, the multiplication factor k for the peripheral
blocks at the respective centers of the upper side, the lower side,
the left side, and the right side is 0.5, and the multiplication
factor k for the other peripheral blocks is one. The luminance of
each of the peripheral blocks is controlled depending on the
multiplication factor k.
In this case, the multiplication factor k is decreased only in the
peripheral block where the peripheral block temperature difference
estimated value Tbd is large, and only the luminance of this
portion is reduced. Consequently, only the luminance of the
peripheral block most easily damaged is lowered without lowering
the luminance of the other block, thereby making it possible to
more reliably prevent the PDP 11 from being damaged.
A second luminance control method for the plasma display device
will be described. The second luminance control method is for
controlling luminance for each peripheral block on the basis of a
peripheral block temperature difference estimated value Tbd'
obtained by subjecting a peripheral block temperature difference
value Tbd between adjacent peripheral blocks to filtering
processing such that the amount of controlled luminance between the
adjacent peripheral blocks is smoothly changed. In the control
method, the peripheral block temperature difference estimated value
Tbd is subjected to filtering processing such as integration or
interpolation between the adjacent peripheral blocks by the
controller 3, a multiplication factor k corresponding to the
peripheral block temperature difference estimated value Tbd' after
the filtering processing is outputted, and a video signal VS
corresponding to the peripheral block is multiplied by the
multiplication factor k in the multiplication circuit 21.
FIG. 17 is a diagram showing an example of a peripheral block
temperature difference estimated value Tbd for each peripheral
block, a peripheral block temperature difference estimated value
Tbd' after filtering processing, and a multiplication factor k in a
case where luminance is controlled for each peripheral block such
that the amount of controlled luminance is smoothly changed by the
second luminance control method.
First, as shown in FIG. 17(a), it is assumed that a peripheral
block temperature difference estimated value Tbd is estimated for
each peripheral block, as in FIG. 16(a). The peripheral block
temperature difference estimated value Tbd is then filtered by
interpolation between the adjacent peripheral blocks. The
peripheral block temperature difference estimated value Tbd' after
the filtering processing is as shown in FIG. 17(b). A peripheral
block. temperature difference estimated value Tbd for the
peripheral block between the peripheral block having a peripheral
block temperature difference estimated value Tbd of 20 and the
peripheral block having a peripheral block temperature difference
estimated value Tbd of 0 is interpolated from zero to 10. In this
case, a multiplication factor k for each of the peripheral blocks
is as shown in FIG. 17(c). That is, the multiplication factor k for
the peripheral blocks at the respective centers of the upper side,
the lower side, the left side and the right side is 0.5, the
multiplication factor k for the peripheral block positioned at each
vertex of the display screen is one, and the multiplication factor
k for the intermediate peripheral block is 0.75. The multiplication
factor k is smoothly changed. The luminance of each of the
peripheral blocks is controlled depending on the multiplication
factor k.
In this case, the luminance of a portion of the peripheral block
most easily damaged is most greatly reduced, and thermal stress in
the peripheral block is smoothly changed, thereby making it
possible to more reliably prevent the PDP 11 from being damaged.
Further, the multiplication factor k is gradually smoothly changed.
Accordingly, the change in the luminance by the change in the
multiplication factor k is difficult to visually know, thereby
making it possible to prevent the image quality from being
degraded. The change in the multiplication factor k by the
filtering processing is not particularly limited. Various
modifications are possible. For example, the multiplication factor
k is exponentially changed.
Description is now made of a plasma display device according to a
third embodiment of the present invention. FIG. 18 is a block
diagram showing the configuration of the plasma display device
according to the third embodiment of the present invention.
The plasma display device shown in FIG. 18 divides a display screen
of a display 1 into a plurality of blocks, finds a peripheral block
temperature difference estimated value Tbd for each peripheral
block adjacent to the outer periphery of the display screen out of
the blocks obtained by the division, extracts the maximum
peripheral block temperature difference estimated value Tmax out of
the peripheral block temperature difference estimated values Tbd,
and controls luminance using the maximum peripheral block
temperature difference estimated value Tmax. Consequently, the
plasma display device shown in FIG. 18 is the same as the plasma
display device shown in FIG. 13 except that the temperature
difference estimator 4A is changed into a temperature difference
estimator 4B for estimating the peripheral block temperature
difference estimated value Tbd for each peripheral block and
extracting the maximum peripheral block temperature difference
estimated value Tmax. Accordingly, the same portions are assigned
the same reference numerals and hence, the description thereof is
not repeated. Only the temperature difference estimator 4B obtained
by the change will be described in detail.
FIG. 19 is a block diagram showing the configuration of the
temperature difference estimator 4B shown in FIG. 18. The
temperature difference estimator 4B shown in FIG. 18 is the same as
the temperature difference estimator 4A shown in FIG. 14 except
that a maximum selector 46 is added in a stage succeeding a
subtracter 44. Accordingly, the same portions are assigned the same
reference numerals and hence, the description thereof is not
repeated.
As shown in FIG. 19, the maximum selector 46 is connected to the
subtracter 44, and selects a maximum peripheral block temperature
difference estimated value Tb out of the peripheral block
temperature difference estimated values Tbd for the peripheral
blocks in one field, that is, one display screen which are
outputted from the subtracter 44 and extracts the maximum
peripheral block temperature difference estimated value Tbd as a
maximum peripheral block temperature difference estimated value
Tmax.
FIG. 20 is a diagram showing an example of a temperature estimated
value Tb, a peripheral block temperature difference estimated value
Tbd, and a maximum peripheral block temperature difference
estimated value Tmax which are estimated for each peripheral
block.
As shown in FIG. 20(a), it is assumed that a temperature estimated
value Tb is estimated for each peripheral block, as in FIG. 15(a).
As shown in FIG. 20(b), a peripheral block temperature difference
estimated value Tbd for each peripheral block is then found, as in
FIG. 15(b). Finally, a peripheral block at the lower left corner
having a maximum peripheral block temperature difference estimated
value Tbd (13 in the example shown in FIG. 20) out of peripheral
block temperature difference estimated values Tbd shown in FIG.
20(b) is selected, and 13 which is the peripheral block temperature
difference estimated value Tbd for the peripheral block is taken as
the maximum peripheral block temperature difference estimated value
Tmax.
As a result, as shown in FIG. 20(C), the peripheral block
temperature difference estimated values Tbd for all the peripheral
blocks are replaced with the maximum peripheral block temperature
difference estimated value Tmax. A multiplication factor k is
determined, as in FIG. 8, for each peripheral block using the
maximum peripheral block temperature difference estimated value
Tmax, and the luminance of each of the peripheral blocks is
controlled depending on the multiplication factor k.
A controller 3 uses the maximum peripheral block temperature
difference estimated value Tmax found in the above-mentioned
manner, to output a brightness control signal LC to a brightness
controller 2 such that the luminance is controlled for each
peripheral block. The brightness controller 2 outputs to a display
1 an address driver driving control signal AD, a scan driver
driving control signal CS, and a sustain driver driving control
signal US for controlling luminance for each peripheral block
depending on the brightness control signal LC. In the display 1,
the luminance is controlled in response to each of the inputted
driving control signals.
The present embodiment is the same as the second embodiment except
that a temperature difference estimator 4B corresponds to a
temperature estimation circuit and an operation circuit.
In the plasma display device configured as described above, the
luminance control method for each of the above-mentioned
embodiments can be used, thereby making it possible to obtain the
same effect.
In the present embodiment, the luminance is controlled using the
maximum peripheral block temperature difference estimated value
Tmax representing the largest temperature difference in the
peripheral blocks, thereby making it possible to more reliably
prevent the PDP 11 from being damaged. Further, the luminance is
controlled by one maximum peripheral block temperature difference
estimated value, so that processing for controlling the luminance
is simplified.
Description is now made of a plasma display device according to a
fourth embodiment of the present invention. FIG. 21 is a block
diagram showing the configuration of the plasma display device
according to the fourth embodiment of the present invention.
The plasma display device shown in FIG. 21 is the same as the
plasma display device shown in FIG. 1 except that a temperature
measuring unit 6 is added. Accordingly, the same portions are
assigned the same reference numerals and hence, the description
thereof is not repeated.
As shown in FIG. 21, the temperature measuring unit 6 is connected
to a panel periphery temperature setter 5, and directly measures
the temperature of the panel outer periphery of a PDP 11 and
outputs the measured temperature to the panel periphery temperature
setter 5. The panel periphery temperature setter 5 sets a reference
value To corresponding to the measured temperature and outputs the
set reference value To to a temperature difference estimator 4.
After that, the subsequent processing is performed, as in the first
embodiment, so that luminance is controlled.
The present embodiment is the same as the first embodiment except
that the panel periphery temperature setter and the temperature
measuring unit 6 correspond to a measurement circuit.
In the plasma display device configured as described above, the
luminance control method in the first embodiment can be similarly
used, thereby making it possible to obtain the same effect. When
the temperature measuring unit 6 in the present embodiment is used
for another embodiment, a luminance control method in another
embodiment can be also similarly used, thereby making it possible
to obtain the same effect.
In the present embodiment, the temperature of the panel outer
periphery is directly measured, and the luminance can be controlled
on the basis of the reference value To corresponding to the
temperature. Even when the reference value To is changed due to the
variation in outer air temperature, for example, therefore, the PDP
11 can be more reliably prevented from being damaged. The number of
measuring points in the temperature measuring unit 6 may be one of
plural in the panel outer periphery. When a plurality of points are
measured, a reference value may be set for each of the measuring
points, or a reference value may be set, for example, with respect
to the average of the results of the measurement of the plurality
of points.
Although in each of the above-mentioned embodiments, the video
signal VS is multiplexed by the multiplication factor k included in
the brightness control signal LC outputted from the controller 3 in
the multiplication circuit 21 to control the luminance, the maximum
luminance of an image displayed on the PDP 11 may be lowered by
changing the multiplication circuit 21 into a limiting circuit for
limiting the maximum luminance of the video signal, outputting an
upper-limit value of the maximum luminance corresponding to the
temperature difference estimated value from the controller 3, and
limiting only luminance exceeding the upper-limit value of the
maximum luminance by the limiting circuit.
* * * * *