U.S. patent application number 11/177688 was filed with the patent office on 2005-11-10 for video display device and color temperature correction method for the same.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Kato, Wataru, Kimura, Katsunobu, Matono, Takaaki, Sakai, Takeshi, Takata, Haruki.
Application Number | 20050248688 11/177688 |
Document ID | / |
Family ID | 19059711 |
Filed Date | 2005-11-10 |
United States Patent
Application |
20050248688 |
Kind Code |
A1 |
Kimura, Katsunobu ; et
al. |
November 10, 2005 |
Video display device and color temperature correction method for
the same
Abstract
A video display device that allows the color temperature of the
signals in white color attributes having high luminance and low
chroma saturation to be corrected with high precision is provided
together with the color temperature correction method for the same
so as to visually obtain a desirable white color on display. The
signal processing circuit for the color temperature correction
according to this invention comprises an A/D converter to convert
the video signals as input into digitalized signals, a matrix
circuit to convert the digitalized signals as output from said A/D
converter into luminance signals and at least two color difference
signals, a hue conversion circuit to obtain hue signals from the
color difference signals as output from said matrix circuit, a hue
correction circuit to correct said hue signals, a chroma saturation
conversion circuit to obtain chroma saturation signals from said
color difference signals, a chroma saturation correction circuit to
correct said chroma saturation signals and a color temperature
correction circuit to perform the color temperature correction on
the respective hue and chroma saturation signals as corrected.
Inventors: |
Kimura, Katsunobu; (Tokyo,
JP) ; Matono, Takaaki; (Tokyo, JP) ; Takata,
Haruki; (Tokyo, JP) ; Sakai, Takeshi; (Tokyo,
JP) ; Kato, Wataru; (Tokyo, JP) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
Hitachi, Ltd.
Tokyo
JP
|
Family ID: |
19059711 |
Appl. No.: |
11/177688 |
Filed: |
July 7, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11177688 |
Jul 7, 2005 |
|
|
|
10093668 |
Mar 7, 2002 |
|
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Current U.S.
Class: |
348/655 ;
348/E9.051 |
Current CPC
Class: |
G09G 2320/0666 20130101;
G09G 5/02 20130101; H04N 9/73 20130101 |
Class at
Publication: |
348/655 |
International
Class: |
H04N 009/73 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 27, 2001 |
JP |
2001-226987 |
Claims
What is claimed is:
1. A video display device wherein said device is provided with a
means to correct a color temperature of video signals in white
color attributes having a given luminance or more and a given
chroma saturation or less among said video signals as input.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a method for correcting the
color temperature of the picture signals and a picture display
device of such as a color television receiver and a liquid crystal
projector.
[0002] In such display devices as mentioned above, it is generally
known that an especially bright white color is rendered bluish to
some extent for display thereon by increasing the color temperature
thereof so as to make the pictures visually impressive and
beautiful.
[0003] It is disclosed in the Japanese Unexamined Patent
Publication 23414/1995 that portions in such achromatic colors as
white and gray are detected based on the maximum values of three
types of color difference signals R-Y, G-Y and B-Y in order to
enhance the level of the B-Y so as to strengthen the blue component
of such portions and increase the color temperature thereof.
SUMMARY OF THE INVENTION
[0004] However, the actual pictures include besides a pure white
color a color approximate to white, which color is made with a
slight mixture of other colors with the pure white color and is
hereinafter referred to as approximate white color and also as
white attributes together with the pure white color. It often
happens that what is seen in white in such natural pictures as
scenery and portraits is in actual mostly occupied by the
approximate white rather than the pure white color. In the prior
art as mentioned above, it is arranged such that only the color
temperature of such portions in achromatic colors is increased so
that color temperature correction is performed only on the region
in pure white of the natural pictures, most of which composition is
occupied by such approximate white as mentioned above. Accordingly,
visual effect is not brought by the rise of the color temperature
of such portions to much extent, when the pictures are seen as a
whole.
[0005] Further, there is a case where it appears more beautiful
when the approximate white or slight yellow attribute to the pure
white color that is of low color temperature is altered with bluish
attribute to the pure white color that is of high color
temperature. Moreover, where the display device provided with such
color reproduction characteristics as displaying the portions of a
picture in white attributes by a lower color temperature than the
color temperature of the relevant video signals, such as displaying
the pure white color in yellowish attribute thereto, it is visually
preferable to increase the color temperature of not only the pure
white color, but also that of the approximate white color, the
color temperature of which is low. However, the above prior art is
not so arranged as increasing the color temperature of the
approximate white color, which does not meet such requirement as
mentioned above.
[0006] In view of the above inconveniences as encountered with the
prior art, the present invention is to provide a video display
device that more appropriately corrects the color temperature of
the pictures so as to display them in more preferred colors and a
color temperature correction method for the same.
[0007] The video display device according to the present invention
is characterized in being provided with a signal processing circuit
provided with a color temperature correction circuit that corrects
the color temperature of the input video signals of the white
attributes including the approximate white color having a given
luminance or above and a given chroma saturation or below
[0008] Concretely, the signal processing circuit comprises an A/D
converter that converts an input video signal into a digital
signal, a matrix circuit that converts the digital signal as output
from the A/D converter into a luminance signal and at least two
color difference signals, a hue processing circuit to obtain a hue
signal on the basis of the color difference signal as output from
the matrix circuit, a chroma saturation processing circuit to
obtain a chroma saturation signal on the basis of the color
difference signal and a microcomputer, wherein the color
temperature correction circuit is characterized in performing color
temperature correction processing for the purpose of increasing the
color temperature of the hue signal as output from the hue
processing circuit and the chroma saturation signal as output from
the chroma saturation circuit, which signals belong to the white
attributes, or for the purpose of approximating the color
temperature of the white attributes to that of blue color.
[0009] The color temperature correction circuit comprises a first
color temperature correction section that performs the color
temperature correction on the hue signal as output from the hue
processing circuit, which signal belongs to the white attributes, a
second color temperature correction section that performs the color
temperature correction on the chroma saturation signal as output
from the chroma saturation processing circuit, which signal belongs
to the white attributes, a first selection circuit that selects and
outputs either a signal as output from the first color temperature
correction section or a hue signal as output from the hue
processing circuit and a second selection circuit that selects and
outputs either a signal as output from the second color temperature
correction section or the hue signal as output from the hue
processing circuit. Further, the first and second selection
circuits are arranged such that they select the signals as output
from the first and second color temperature correction sections
where the region of the input video signal, which region belongs to
the white attributes and has a given luminance or above and a given
chroma saturation or below, is detected.
[0010] Further, the color temperature correction method according
to the present invention is characterized in comprising a step of
converting an input video signal into a digital signal, a step of
separating the digital signal into a luminance signal and a color
difference signal, a step of separating the color difference signal
into a hue signal and a chroma saturation signal and a step of
performing color temperature correction processing on the hue and
the chroma saturation signals, which signals belong to the white
attributes and have a given luminance or above and a given chroma
saturation or below, so as to increase the color temperature of the
same signals. The step of performing the color temperature
correction processing may further include a step of approximating
the hue of the signals belonging to the white attributes to blue
color and a step of increasing the chroma saturation of the signals
belonging thereto.
[0011] The present invention is arranged such that the color
temperature correction is performed on the signal, which signal
belongs to the white attributes and has a given luminance or above
and a given chroma saturation or below, which allows the color
temperature of the signal not only in pure white, but also in the
approximate white color with the slight mixture of other colors to
be corrected. Thus, even though pictures like natural scenery and
portraits include a lot of approximately white portions, correcting
the color temperature of such approximate white color so as to
increase or approximate the same color to blue allows a visually
preferred white color to be obtained, with the result that more
beautiful video pictures can be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a block diagram to show one embodiment of the
signal processing circuit for the video display device according to
the present invention.
[0013] FIG. 2 is a view to show a hue circle that denotes colors in
vector.
[0014] FIG. 3 is a view to show one example of the correlation
between a hue signal and a chroma saturation signal.
[0015] FIG. 4 is a view to show the input and output
characteristics of the respective sections of the hue correction
circuit 20.
[0016] FIG. 5 is a view to show the input and output
characteristics of the respective sections of the hue correction
circuit 20.
[0017] FIG. 6 is a view to show the range of the signals belonging
to the white attributes as detected by the detection circuit
17.
[0018] FIG. 7 is a block diagram to show the details of the first
color temperature correction section 231.
[0019] FIG. 8 is a view to show the operation of the first color
temperature correction section 231.
[0020] FIG. 9 is a view to show the input and output
characteristics of the respective sections of the first color
temperature correction section 231.
[0021] FIG. 10 is a view to show the input and output
characteristics of the second and third hue shift coefficient
generation circuits 2341 and 2342.
[0022] FIG. 11 is a block diagram to show the details of the second
color temperature correction section 235.
[0023] FIG. 12 is a view to show the input and output
characteristics of the respective sections of the second color
temperature correction section 235.
[0024] FIG. 13 is a view to show the input and output
characteristics of the respective sections of the chroma saturation
correction circuit 22.
[0025] FIG. 14 is a block diagram to show another embodiment of the
present invention.
[0026] FIG. 15 is a view to show the range of the signals belonging
to the white attributes as detected by the detection circuit
17'.
[0027] FIG. 16 is a block diagram to show another embodiment of the
present invention.
[0028] FIG. 17 is a block diagram to show the details of the
luminance correction circuit 151.
[0029] FIG. 18 is a view to show the input and output
characteristics of the respective sections of the luminance
correction circuit 151.
BEST MODE FOR CARRYING OUT THE INVENTION
[0030] Hereinafter, the preferred embodiments of the present
invention are described below with reference to the accompanying
drawings. FIG. 1 is a block diagram to show one embodiment of the
signal processing circuit for the video display device according to
the present invention. The R, G and B primary colors signals, which
are input to an R terminal 11, a G terminal 12 and a B terminal 13
respectively, are supplied to an A/D conversion circuit 14 so as to
be converted into digital signals. A matrix conversion circuit 15
subjects the three primary colors signals (R, G, B) in digital form
as output from the A/D conversion circuit 14 to matrix conversion
processing so as to convert the same signals into a luminance
signal Y as well as color difference signals (R-Y) and (B-Y), which
luminance signal Y is output to a detection circuit 17 and an
inverse matrix conversion circuit 27 respectively and which color
difference signals (R-Y) and (B-Y) are output to a hue conversion
circuit 18 and a chroma saturation conversion circuit 21
respectively. The hue conversion circuit 18 performs an attribute
conversion operation as shown in the following equation 1, for
instance, with the input (R-Y) and (B-Y) signals in use so as to
output a hue signal () in digital form.
=tan.sup.-1 {(R-Y)/(B-Y)} (Equation 1)
[0031] On the other hand, the chroma saturation circuit 21 performs
an attribute conversion operation as shown in the following
equation 2, for instance, with the input (R-Y) and (B-Y) signals in
use so as to output a chroma saturation signal (S) in digital
form.
S={square root}{square root over ((R-Y).sup.2+(B-Y).sup.2)}
(Equation 2)
[0032] Hereafter, the hue and chroma saturation signals are
described. As shown in FIG. 2, when the (B-Y) signal is taken on
the horizontal axis while the (R-Y) signal is taken on the vertical
axis, colors are represented with vectors. The direction of the
respective vectors or an angle that the horizontal axis (B-Y) makes
with the respective vectors indicates a hue () and the largeness of
the respective vectors indicates chroma saturation (S). What colors
are represented with vectors is called a hue circle, which is
generally known. In this hue circle, for instance, magenta is
represented with a vector locating by 45.degree. apart from the
(B-Y) axis as shown in FIG. 2. That is, the hue () of the magenta
is at 45.degree.. The chroma saturation (S) is determined by the
largeness of the respective vectors wherein the larger the vector
is, the denser it is while the smaller it is, the dimmer it is. If
the largeness of a vector is null, it shows that there is no color
in issue. The hue of red, yellow, green, cyan, blue respectively is
at 113.2.degree., 173.0.degree., 225.0.degree., 293.2.degree. and
353.0.degree.. The hue conversion circuit 18 outputs a hue signal
in digital form wherein the same circuit outputs the range of hue
from 0.degree. to 359.90 as the digital signals ranging from 0 to
1023, given that the digital signal is in 10 bits precision. That
is, this bit precision divides the hue of 360.degree. by 1024 that
is equivalent to 2 to the tenth power. The LLSB of the hue digital
signal amounts to approximately 0.350.
[0033] FIG. 3 is a view to supplement what is described above, in
which one example of the correlation between the hue signal and the
chroma saturation signal is shown by a waveform 301.
[0034] FIG. 3 takes the hue signal (in 10 bits precision) on the
horizontal axis thereof while taking the chroma saturation signal S
(8 bits in precision) on the vertical axis thereof. The
representative hues (B-Y), (R-Y), -(B-Y) and -(R-Y) are shown
therein as 0, 256, 512 and 768 respectively.
[0035] On the other hand, the chroma saturation circuit 21 outputs
the chroma saturation signals that indicate the largeness of the
vectors corresponding to the hue signals ranging from 0 to 1023 as
the corresponding digital signals. Given that this chroma
saturation signals in digital form are in 8 bits precision, the
chroma saturation circuit 21 outputs the corresponding digital
signals ranging from 0 to 255.
[0036] The digitalized hue signals as output from the hue
conversion circuit 18 are input to a hue correction circuit 20,
which circuit is provided with a local hue correction circuit 203
as well as adders 201 and 202 so as to correct and output the
digitalized hue signals as input within the specific range of hue.
The range of hue as corrected and the degree of correction as
effected by the hue correction circuit 20 are determined by the
variety of the set values as output from a microcomputer 40. Then,
the digitalized chroma saturation signals as output from the chroma
saturation circuit 21 are input to a chroma saturation correction
circuit 22, which circuit is provided with a chroma saturation
coefficient generation circuit 222 as well as a multiplier 221 and
an adder 223 so as to correct and output the digitalized chroma
saturation signals as input within the specific range of chroma
saturation. The range of chroma saturation as corrected and the
degree of correction as effected by the chroma saturation circuit
are determined by the variety of the set values as output from the
microcomputer 40.
[0037] The digitalized hue signals as corrected (hereinafter,
referred to as corrected hue signals) by the hue correction circuit
20 and the digitalized chroma saturation signals as corrected
(hereinafter, referred to as corrected chroma saturation signals)
are input to a color temperature correction circuit 23, which
circuit is the characteristic portion of the present invention and
is arranged such that color temperature correction is performed on
the corrected hue and chroma saturation signals in the white
attributes having a given luminance or above and a given chroma
saturation or below as defined by the maximum set value of chroma
saturation ST and the minimum set value of luminance YB that are
supplied from the microcomputer 40. Further, the color temperature
correction circuit 23 is provided with a first color temperature
correction section 231 that performs color temperature correction
on the corrected hue signal, a first selection circuit 232 that
selects and outputs either a signal as output from the first color
temperature correction circuit 231 or the corrected hue signal as
output from the hue correction circuit 20, a second color
temperature correction section 235 that performs color temperature
correction on the corrected chroma saturation signal and a second
selection circuit 236 that selects either a signal as output from
the second color temperature correction section 235 or the
corrected chroma saturation signal as output from the chroma
saturation circuit 22. The first and second selection circuits 232
and 236 select and output the signals as output from the first
color correction section 231 and the second color correction
section 235 respectively where the input video signals are of a
given luminance or above and a given chroma saturation or below
while otherwise selecting and outputting the corrected hue and
chroma saturation signals respectively. The selection operation of
the signals as mentioned above by means of the first and second
selection circuits 232 and 236 is performed on the basis of the
control signals as output by a detection circuit 17.
[0038] The detection circuit 17 detects whether the input vide
signals are those in the white attributes having a given luminance
or above and a given chroma saturation or below. Concretely, the
detection circuit 17 comprises a luminance comparison circuit 171
that compares a luminance signal as output from a matrix conversion
circuit 15 with the minimum value of luminance YB as set by the
microcomputer 40, a chroma saturation comparison circuit 172 that
compares the corrected chroma saturation signal with the maximum
value of chroma saturation ST as set by the microcomputer and a
switching control circuit 173 to which the signals as output from
the luminance comparison circuit 171 and the chroma saturation
comparison circuit 172 are input, on the basis of which signals the
switching control circuit determines whether the input video
signals meet the condition that they are of a given luminance or
above and a given chroma saturation or below so as to output the
control signals to the first and second selection circuits 232 and
236 where such condition is met. That is, where such condition as
mentioned above is met, the switching control circuit 173 is
arranged such that the first and second selection circuits 232 and
236 select and output the signals as output from the first and
second color correction sections 231 and 235 respectively.
[0039] The signals as output from the first and second selection
circuits 232 and 236 are input to a color difference conversion
circuit 26, which circuit generates the color difference signals
(R-Y) and (B-Y) from those output signals and outputs them. The
color difference signals as output from the color difference
conversion circuit 26 are input to an inverse matrix conversion
circuit 27 so as to be converted into three primary colors signals
of R, G and B. The three primary colors signals as output from the
inverse matrix conversion circuit 27 are supplied to a display
device 28, which device displays video pictures on the basis of
those three primary colors.
[0040] Then, the respective sections of the device are in more
details described below. Firstly, the hue correction circuit 20 is
described in details with reference to FIGS. 4 and 5. The hue
correction circuit, where there is no addition to the digitalized
hue signal at the adders 201 and 202, is possessed with the linear
input and output characteristics as shown in the straight line 401
of FIG. 4A. The digitalized hue signal as output from the hue
conversion circuit 18 is input to the adder 201 and the local hue
correction circuit 203 respectively. The local hue correction
circuit 203, to which a mean value HP of hue, a level H thereof and
a width W thereof as shown in FIG. 4B as output from the
microcomputer 40 are input, decodes hue within the range of such
input data so as to output a signal having a waveform as shown in
402 of FIG. 4B. The adder 201 adds the digitalized hue signal to
the signal as output from the local hue correction circuit 203
having such trapezoidal waveform 402. As the result of it, the
adder 201 outputs a signal having a waveform 501 that shifts by H
upwards in the interval W with the middle HP thereof as shown in
FIG. 5A. The degree to which the waveform shifts depends on the
level H as input from the microcomputer 40. In this way, the local
hue correction circuit 203 and the adder 201 variably control hue
within the range as designated by the microcomputer 40 and with a
level as designated by the same so as to allow hue to be locally
controlled.
[0041] Further, the signal having the waveform 501 as output from
the adder 201 is input to one terminal of the adder 202. To the
other terminal of the adder 202, an offset value as output from the
microcomputer 40 is input. This offset value is possessed with a
given level a over the whole hue as shown in the straight line 502
of FIG. 5B. The adder 202 adds the signal as output from the adder
201 to the offset value as output from the microcomputer 40, which
results that the adder 202 outputs a signal that shifts upwards the
whole signal as shown in FIG. 5A by the level a of the offset value
as shown in FIG. 5C with a waveform 503. In this way, the adder 202
allows the overall hue to be controlled, the function of which
corresponds to a so-called tint adjustment for the purpose of
adjusting the overall hue. To note, the adder 202 according to the
present embodiment adopts a 10 bits adder for both input and output
operations so that it overflows and returns to 0 when the addition
result goes beyond 1023. Accordingly, where the addition by means
of the adder 202 results in being over 1023, it outputs a value
that subtracts 1023 from the addition result.
[0042] As mentioned above, the hue correction circuit 20 varies the
hue signal within the range of hue as designated by the
microcomputer 40 with that of another hue and outputs a signal that
offsets the whole hue by a given value by setting such offset
value. The use of the 10 bits digital signal for the hue signal
allows s high-precision hue shift and offset control as per
approximately 0.350 to be realized. Such parameters relating to the
hue correction as the degree to which and the range within which
the hue shifts are set by the microcomputer 40, which parameters
are arbitrarily altered and adjusted. To note, there is only one
range within which hue shifts according to the present embodiment,
but the plurality of the local hue correction circuits 203 may be
provided, the signals as output from which circuits are added so as
to be input the adder 201, which allows the plural ranges of hue to
be shifted independently from one another.
[0043] Then, the chroma saturation circuit 22 is described below in
details with reference to FIG. 13. The chroma saturation circuit
22, where there is neither addition to the digitalized chroma
saturation signal at an adder 223 nor multiplication performed
thereon at a multiplier 221, is possessed with the linear input and
output characteristics as shown in FIG. 13A with a straight line
1201A. The digitalized chroma saturation signal as output from the
chroma saturation circuit 21 is input to the multiplier 221 of the
chroma saturation correction circuit 22. On the other hand, the
digitalized hue signal as output from the hue conversion circuit 18
is input to a local chroma saturation correction circuit 222, to
which circuit a mean value HP of hue, a level H thereof and a width
W thereof as designated by the microcomputer 40 and as shown in
FIG. 13B are input and which circuit decodes hue within the range
of the input data so as to output a correction signal for locally
correcting the chroma saturation of the hue of the specific range,
which signal is shown in FIG. 13B with a waveform 1202A. An adder
223 adds an offset value as output from the microcomputer 40 to a
signal as output from the local chroma saturation signal correction
circuit 222. As the result of it, the adder 223 outputs a chroma
saturation amplification coefficient with the characteristics as
shown in FIG. 13C with a waveform 1203A. Accordingly, it is the
level H that determines the amplification degree of the chroma
saturation signal within the specific range of hue while it is the
off set value as designated by the microcomputer 40 that determines
the amplification degree of the overall chroma saturation signals
(or chroma saturation signals over the whole hue). This offset
value is constant over the whole hue, the level of which value is
set at 128 that is in the middle between the minimum value (0) and
the maximum value (255) of the chroma saturation signals in the
present embodiment. The signal as output from the adder 223 (chroma
saturation amplification coefficient) is input to one terminal of
the multiplier 221, to the other terminal of which the digitalized
chroma saturation signal as output from the chroma saturation
conversion circuit 21 is input. The multiplier 221, which
multiplies the digitalized chroma saturation signal by the chroma
saturation amplification coefficient, shifts or corrects the chroma
saturation level within the specific range of hue.
[0044] In this way, the chroma saturation correction circuit 22
locally corrects the chroma saturation signal within the range of
hue as designated so as to vary the density of the color within the
specific range of hue, which circuit also controls the chroma
saturation signals of the whole hue so as to vary the density of
the color over the whole hue. This function corresponds to a
so-called color adjustment. Further, such parameters relating to
chroma saturation correction as the degree to which and the range
within which the chroma saturation is corrected are designated by
the microcomputer 40, which allows those parameters to be altered
and adjusted. To note, there is only one range for chroma
saturation correction in the present embodiment, but the plural
local chroma saturation circuits may be provided, the signals as
output from which circuits are added so as to be input to the
multiplier 221, which allows the chroma saturation within the
plural ranges of hue to be independently corrected.
[0045] Then, the detection circuit 17 is described below in details
with reference to FIG. 6. The luminance signal Y as output from the
matrix conversion circuit 15 is input to a luminance level
comparison circuit 171, which circuit compares the luminance signal
Y with the minimum set value of luminance YB (601) as shown in FIG.
6 so as to output a high luminance level detection signal `1` where
the luminance signal Y is larger than the set value YB while to
output `0` otherwise. The minimum set value of luminance YB is
defined as 210 in the present embodiment, which corresponds to the
70% of the maximum luminance 100. That is, the present embodiment
is intended for detecting the signals in the white attributes
having 70% or more of luminance, to which value it is not
necessarily limited, but may adopt other value where
appropriate.
[0046] In turn, the chroma saturation signal as output from the
multiplier 221 of the chroma saturation circuit 22 is input to a
chroma saturation level comparison circuit 172, which circuit
compares the chroma saturation signal with the maximum set value of
chroma saturation ST (602) as shown in FIG. 6 so as to output a low
chroma saturation level detection signal `1` where the chroma
saturation signal is smaller than the set value ST while to output
`0` otherwise. The maximum set value of chroma saturation ST is
defined as 10 in the present embodiment, which value corresponds to
the color temperature of 4000 K (Kelvin) for the signals in
yellowish white. That is, the present embodiment is intended for
detecting the signals in the white attributes, the color
temperature of which signals is 4000 K or more, to which value it
is not necessarily limited, but may adopt other value in an
arbitrary manner. Further, the same set value of the color
temperature may be applied to the whole hue whereas the different
set value thereof may be applied to the specific range of hue. For
instance, the set value of the color temperature for the signals in
bluish white may be 20000 K.
[0047] Both the high luminance level detection signal and the low
chroma saturation level detection signal are input to the switching
control circuit 173, which circuit performs an AND operation on
those detection signals so as to determine whether the input video
signals are those in the white attributes having a given luminance
or above and a given chroma saturation or below, in other words,
those in very bright and very dim white. In short, the switching
control circuit 173 discerns whether the input video signals exist
within a cylindrical area drawn with the slanting lines as shown in
FIG. 6, which area belongs to the signals in the white attributes,
and outputs a flag signal `1` when the input video signal is within
the same area, which means that those two detection signals amount
to `1` while outputting a flag signal `0` when it is out of the
same area, which means that either of them or both of them amount
to `0`. Either of those flag signals is supplied to the first and
second selection circuits 232 and 236 of the color temperature
correction circuit 23 for the purpose of controlling the same
selection circuits.
[0048] The detection circuit 17 according to the present embodiment
detects the video signals having chroma saturation of the maximum
set value thereof ST or less as well as luminance of the minimum
set value thereof YB or more, which circuit allows not only the
signals in pure white, but also those in the white attributes with
the slight mixture of other color as well as in the white
attributes of lower luminance with the slight mixture of gray. The
minimum set value of luminance YB and the maximum set value of
chroma saturation ST that are the criteria for detecting the
signals in the white attributes are designated by the microcomputer
40, which allows the range of the signals in the white attributes
as required to be designated in an arbitrary and high precision
manner. Further, such sufficiently colored picture area as a human
skin, the chroma saturation signal of which area is large in
amplitude level and the luminance signal of which area is not of
extreme largeness, can be excluded from the detection range of the
signals in the white attributes depending on the set values of ST
and YB.
[0049] Then, the color temperature correction circuit 23 is
described below in details with reference to FIGS. 7 through 11.
Firstly, a first color temperature correction section 231 to
perform the color temperature correction of the hue signal is
described with reference to FIGS. 7 through 10. The first color
temperature correction section 231 is arranged such that it takes a
hue indicated with the vector 801 in FIG. 8A (hue of blue herein)
as a reference hue and generates a hue shift coefficient that
aggregates to the same reference hue its peripheral hue. FIG. 7
shows one example of the circuit arrangement thereof.
[0050] In FIG. 7, the corrected hue signal as output from the adder
202 of the hue correction circuit 20 is input to a hue input
terminal 2312 of the first color temperature correction section
231, which corrected hue signal is supplied to one terminal of an
adder 2322. To the other terminal of the adder 2322, the hue offset
value (HUEOFFSET) as set by the microcomputer 40 is input through a
hue offset input terminal 2311, which hue offset value is also
supplied to one terminal of a subtractor 2336. The adder 2322 adds
the corrected hue signal to the hue offset value wherein the hue
offset value as set by the microcomputer 40 is equal to the
difference T between the digitalized value `1024` and the hue value
of the reference vector 801 as shown in FIG. 8A, which offset value
is found by the following equation, for instance.
HUEOFFSET(T)=1024-(353/360).multidot.1024=20
[0051] Thus, the adder 2322 outputs the digitalized value `0` as
shown in FIG. 8B with a vector 802, when a signal having the hue
value of the vector 801 is input thereto. This indicates that the
vector 801 has counterclockwise rotated by the value T to the
position of the vector 802 on the (B-Y) axis. The hue signal that
has rotated by the hue offset value as a whole by the adder 2322 is
input to the subtractor 2323 comprising a first hue shift
coefficient generation circuit 2340.
[0052] Hereafter, the operation of the first hue shift coefficient
generation circuit 2340 is described. The subtractor 2323 outputs a
hue signal with 512 subtracted from the hue signal as output from
the adder 2322. At the same time, the subtractor 2323 outputs the
digitalized value `1` as a code signal when the subtraction turns
out to be positive while outputting the digitalized value 10'
otherwise. The hue signal as subtracted and output as well as
either one of those code signals are input to an absolute value
circuit 2324, which circuit outputs the input signal as it is when
the subtraction turns out to be positive while otherwise subjecting
the input signal to the absolute value operation because of it is
negative before outputting the same signal. The hue component as
subjected to the absolute value operation at the circuit 2324 is
input to a multiplier 2325 and multiplied by a hue multiplication
coefficient as input from the microcomputer 40 through an input
terminal 2313 so as to be subjected to gain adjustment. The
multiplier 2325 outputs the hue component as subjected to the gain
adjustment to the first input terminal of a selection circuit 2332.
In this way, the first hue shift coefficient generation circuit
2340 is arranged such that it generates such a hue shift
coefficient as rendering the smallest degree of hue shift the hue
that is dislocated by 180.degree. from the hue value in the
vicinity of blue corresponding to the vector 801 as shown in FIG.
8A and as set by the microcomputer 40 or by 512 in the terms of the
digitalized value and rendering the degree of hue shift greater as
the hue gets nearer to the same hue value as dislocated by
180.degree. therefrom. This hue shift coefficient is subjected to
the gain adjustment by the multiplier 2325. The hue multiplication
coefficient for this gain adjustment is adjustable by the
microcomputer 40.
[0053] The second hue shift coefficient generation circuit 2341
outputs a differential signal with the luminance signal Y greater
than the minimum set value of luminance YB that is used for
detecting the signals in the white attributes in the aforementioned
detection circuit 17. This generation circuit renders the level of
this differential signal null when the luminance signal is smaller
than the minimum set value of luminance YB and generates a hue
shift coefficient in proportion to the largeness of this
differential signal. The gain adjustment for this hue coefficient
is also operable by the microcomputer 40. Hereafter, the second hue
coefficient generation circuit 2341 is described in details. The
luminance signal Y as output from the aforementioned matrix
conversion circuit 15 is supplied through a luminance input
terminal 2314 to a subtractor 2326, to the other input terminal
2315 of which subtractor the minimum set value of luminance YB is
supplied. This subtractor subtracts the set value of luminance YB
from the luminance signal Y so as to output a differential signal,
which differential signal is supplied to a clipping circuit 2327,
which circuit clips off the negative value of the input luminance
differential signal into null so as to output a positive
differential signal. The signal as output from this clipping
circuit is input to a multiplier 2328 and is multiplied by the
luminance multiplication coefficient as input from the
microcomputer 40 so as to be subjected to the gain adjustment. The
multiplier 2328 outputs the luminance component as subjected to the
gain adjustment to the second input terminal of the selection
circuit 2332 as a hue shift coefficient. The straight line 1001 of
FIG. 10A shows the input and output characteristics of the second
hue shift coefficient generation circuit 2341. It is a luminance
multiplication coefficient that adjusts the inclination of the
straight line 1001. As described above, the second hue shift
coefficient generation circuit 2341 outputs a hue shift coefficient
that becomes greater invalue as the level of luminance signal
becomes greater where the level thereof is at the minimum set value
of luminance YB or more. To note, where the level thereof is at the
minimum set value of luminance YB or less, the generation circuit
outputs the digitalized value of 0 wherein the degree of hue shift
is also 0.
[0054] The third hue shift coefficient generation circuit 2342
generates a hue shift coefficient on the basis of a differential
signal with the chroma saturation signal that is smaller than the
maximum set value of chroma saturation ST as used for detecting the
signals in the white attributes in the aforementioned detection
circuit 17. This differential signal amounts to null together with
the degree of hue shift when the chroma saturation signal is
greater than the maximum set value of chroma saturation ST.
Hereafter, the third hue shift coefficient generation circuit 2342
is described in details. The corrected chroma saturation signal as
output from the multiplier 221 of the aforementioned chroma
saturation correction circuit is supplied through a chroma
saturation input terminal 2318 to one input terminal of a
subtractor 2329, to the other terminal of which subtractor the
maximum set value of chroma saturation ST is supplied through an
input terminal 2317. The subtractor 2329 subtracts the maximum set
value ST from the corrected chroma saturation signal so as to
output a differential signal as obtained to a clipping circuit
2330, which circuit clips off the negative value of the input
differential signal into null so as to output a positive
differential signal only. The differential signal as output from
the clipping circuit 2330 is input to a multiplier 2331, which
multiplier multiplies this differentia signal by a chroma
saturation multiplication coefficient as supplied through an input
terminal 2319 from the microcomputer 40 so as to perform the gain
adjustment. The chroma saturation component as subjected to the
gain adjustment by the multiplier 2331 is supplied to a third input
terminal of the selection circuit 2332. The straight line 1002 of
FIG. 10B shows the input and output characteristics of the third
hue shift coefficient generation circuit 2342. The inclination of
the straight line 1002 is adjusted by a chroma saturation
multiplication coefficient. In this way, where the level of chroma
saturation signal is smaller than the maximum set value of chroma
saturation ST, the third hue shift coefficient generation circuit
2342 generates a hue shift coefficient that becomes greater in
value as the level thereof becomes smaller. Otherwise, the same
circuit outputs the digitalized value of 0 wherein the degree of
hue shift also amounts to null.
[0055] The selection circuit 2332 selects a signal having either
the maximum degree of hue shift or the minimum degree thereof from
the signal as input to the first terminal thereof (or as output
from the first hue shift coefficient generation circuit 2340), that
as input to the second terminal thereof (or as output from the
second hue shift coefficient generation circuit 2341) and that as
input to the third terminal thereof (or as output from the third
hue shift coefficient generation circuit 2342 so as to output the
same signal. The selection operation thereof by means of the
selection circuit 2332 is controlled in accordance with a switching
control signal as input thereto through an input terminal 2321 from
the microcomputer 40. In order to facilitate the explanation on the
processing of the signal as selected by the selection circuit 2332,
it is described below with reference to FIG. 9 on the assumption
that the same circuit selects the signal as input to the first
terminal thereof. FIG. 9 shows the input and output characteristics
of the respective sections of the first color temperature
correction section 231. FIG. 9A shows the input and output
characteristics of an adder 2322 wherein the hue offset value
amounts to null. FIG. 9B shows the input and output characteristics
of the first hue shift coefficient generation circuit 2340 while
FIG. 9C showing that of a switching circuit 2335.
[0056] The hue component as output from the multiplier 2325 is
input through the selection circuit 2332 to a subtractor 2333 and
an adder 2334. The hue signal as output from the adder 2322 is
input to the subtractor 2323 as well as to the subtractor 2333 and
the adder 2334. The subtractor 2333 subtracts the signal as output
from the selection circuit 2332 from the hue signal as output from
the adder 2322. If the subtraction result turns out to be negative,
it is clipped off into null by an integrated clipping circuit,
which is not shown in the drawings, so as to be output to an input
terminal A of the switching circuit 2335. Then, the adder 2334 adds
the hue signal as output from the adder 2322 to the signal as
output from the selection circuit 2332. If the addition result
turns out to be over 1023, it is clipped off into the maximum value
of 1023 by an integrated clipping circuit, which is not shown in
the drawings, so as to be output to an input terminal B of the
switching circuit 2335. When the value of the code signal as output
from the subtractor 2323 amounts to 1 or the subtraction result
turns out to be positive, the switching circuit 2335 selects and
outputs the signal as input to the terminal B while amounting to 0
or the subtraction result turns out to be negative, the same
circuit selects and outputs the signal as input to the terminal
A.
[0057] That is, the subtractor 2333 subtracts the signal as shown
in FIG. 9A with a waveform 901 together with that as shown in FIG.
9B with a waveform 902 during the subtraction period of FIG. 9B or
within the output range of the adder 2322 from 0 to 512 and outputs
the subtraction result to the input terminal A of the switching
circuit 2335. In turn, the adder 2334 adds the signal as shown in
FIG. 9A with a waveform 901 to that as shown in FIG. 9B with a
waveform 902 during the addition period of FIG. 9B or within the
output range of the adder 2322 from 513 to 1023 and outputs the
addition result to the input terminal B of the switching circuit
2325. The switching circuit 2335 switches over to and outputs
either one of the signal as input to the terminal A (as output from
the subtractor 2333) and that as input to the terminal B (as output
from the adder 2334) according to the code signal as output from
the subtractor 2323. That is, the same circuit selects the signal
as input to the terminal A within the output range of the adder
2322 from 0 to 512 while selecting that as input to the terminal B
within that from 513 to 1023. As the result of it, the switching
circuit 2335 outputs a signal as shown in FIG. 9C with a waveform
903 wherein the hue has rotationally moved to the direction of 0.
The rotational movement of the hue is shown in FIGS. 8C and D. A
waveform 803 of FIG. 8C shows the state where the rotational
movement of the hue becomes greater as the hue gets nearer to the
(B-Y) axis.
[0058] The state where the hue rotationally moves is described
below with concrete numerical values in use, given that the hue
offset value is 0 and the multiplication coefficient to be
multiplied by the multiplier 2325 is 1.
[0059] Where the corrected hue signal amounts to 10 in value or has
a hue closer to blue, the subtractor 2323 performs the operation of
10-512 and outputs -502 as the result of the operation while
outputting 0 as the code signal thereof. The absolute value circuit
converts -502 into 502 so as to output the same to the subtractor
2333 and the adder 2334. The subtractor 2333 performs the operation
of 10-502, which results in being negative or -492, so as to output
0 to the terminal A of the selection circuit 2335. On the other
hand, the adder 2334 performs the operation of 10+502, which
results in being 512, so as to output the same result to the
terminal B thereof. The selection circuit 2335 selects and outputs
the signal as input to the terminal A or 0 as the code signal as
output from the subtractor 2323 is 0.
[0060] Where the corrected hue signal amounts to 600 or has a hue
comparatively closer to yellow, the subtractor 2323 performs the
operation of 600-512 and outputs 88 as the result of the operation
while outputting 1 as the code signal thereof. The absolute value
circuit outputs 88 as it is and supplies the same to the subtractor
2333 and the adder 2334. The subtractor 2333 performs the operation
of 600-88 and outputs 512 as the result of the operation to the
terminal A of the selection circuit 2335. On the other hand, the
adder 2334 performs the operation of 600+88 and outputs 688 as the
result of the operation to the terminal B thereof. The selection
circuit 2335 selects and outputs the signal as input to the
terminal B or 688 as the code signal as output from the subtractor
2323 is 1.
[0061] As described above, the present embodiment is arranged such
that the color temperature of the hues more distinct from blue
increases with the smaller degree of shift so as not to change the
hues to great extent while bring arranged such that the hues close
to blue have the larger degree of shift so as to come much closer
to blue.
[0062] FIG. 8D shows the rotational movement of the hues as made by
a subtractor 2336, which subtractor moves rotationally and
clockwise by the hue offset value the waveform 803 as shown in FIG.
8C.
[0063] The first color temperature correction section 231 is
intended for rotationally moving the hue of the color difference
signals having a given luminance (the minimum set value of
luminance YB) or more and a given chroma saturation (the maximum
set value of chroma saturation ST) or less to the direction of blue
color for the purpose of increasing the color temperature of the
same signals.
[0064] In the above explanation of the first color temperature
correction section 231, the case is exemplified where the selection
circuit 2332 selects the signal as output from the first hue shift
coefficient generation circuit 2340, but it ma be where it selects
the signal as output from either the second hue shift coefficient
generation circuit 2341 or the third hue shift coefficient
generation circuit 2342. It may be also prearranged that the
selection circuit 2332 selects one of the signals as output from
the three hue shift coefficient generation circuits in an arbitrary
manner wherein the signal as selected by the selection circuit is
limited to one kind of them irrespective of the scale and state of
the signal as input to the selection circuit 2332. Further, the
selection circuit 2332 may be arranged such it selects the signal
of the maximum output level among the signals as output from three
or two hue shift coefficient generation circuits of arbitrary
choice whereas it may be arranged such that it selects the signal
of the minimum output level among the signals as output from three
or two hue shift coefficient generation circuits of arbitrary
choice.
[0065] Then, one example of the second color temperature correction
section 235 is described in details with reference to FIGS. 11 and
12. The corrected chroma saturation signal as output from the
multiplier 221 of the aforementioned chroma saturation circuit 22
is input through a chroma saturation terminal 2351 to one terminal
of an adder 2356. The chroma saturation differential signal is
output from the terminal 2320 of the first color temperature
correction section 231, which differential signal is input through
a terminal 2352 to one terminal of a multiplier 2355, to the other
terminal of which a multiplication coefficient as output from the
microcomputer 40 is input through a terminal 2353. The multiplier
2355 multiplies the chroma saturation differential signal by the
multiplication coefficient so as to perform the gain adjustment of
the differential signal. The chroma saturation differential signal
as subjected to the gain adjustment by the multiplier 2355 is input
to the other terminal of the adder 2356, which adder adds the
corrected chroma saturation signal to the chroma saturation
differential signal as subjected to the gain adjustment so as to
output the addition result to a clipping circuit 2357. The clipping
circuit 2357, where the addition result by the adder 2356
overflows, clips off the same result at a given maximum value. The
signal as output from the same circuit is supplied through a chroma
saturation coefficient output terminal 2354 to the other terminal
of the switching circuit 236. FIG. 12 shows the input and output
characteristics of the respective sections of the second color
temperature correction section 235. FIG. 12A shows the same
characteristics with a straight line 1201 when the chroma
saturation differential signal amounts to 0 in which no addition is
made to the corrected chroma saturation signal at the adder 2356.
In this case, the second color temperature correction section
outputs the corrected chroma saturation signal as output from the
chroma saturation terminal 2351. FIG. 12B shows the input and
output characteristics of the multiplier 2355 with a straight line
1202. As clear from this drawing, the multiplier 2355 outputs a
signal of the maximum level (ST1) when the chroma saturation signal
amounts to 0 while outputting a signal of smaller level as the
chroma saturation signal gets larger in value. FIG. 12C shows the
input and output characteristics of the second color temperature
correction section wherein the characteristics thereof is shown
therein with a kinked line when the signal as output from the
multiplier 2355 is added to the corrected chroma saturation signal
by the adder 2356.
[0066] As described above, the second color temperature correction
section 235 performs the color temperature correction on the chroma
saturation signal, which section is intended for increasing the
chroma saturation of the signals having a given chroma saturation
(the maximum set value of chroma saturation ST) or less so as to
make denser in blue the signals in the white attributes whose hue
is shifted to the direction of blue color by means of the first
color temperature correction section 231 and to render the pictures
on disply vividly in white color. This color temperature correction
is effective for the case where the chroma saturation level of blue
color is originally lower. Such correction for enhancing the chroma
saturation thereof is not required for the white color with higher
chroma saturation level of blue color (blue enough to be
discernible) and/or that intense in warm colors attributes.
[0067] When the flag signal as output from the detection circuit 17
corresponds to 1 or where the input signal of high luminance and
low chroma saturation is detected, the first selection circuit 232
selects and outputs the signal as output from the first color
temperature correction section 231. On the other hand, when the
flag signal corresponds to 0 or where the input signal out of high
luminance and low chroma saturation is detected, the first
selection circuit 232 selects and outputs the signal as output from
the hue correction circuit 20. In synchronization with this
selection control, when the flag signal corresponds to 1, the
second selection circuit 236 selects and outputs the signal as
output from the second color temperature correction section 235
while selecting and outputting the signal as output from the chroma
saturation correction circuit 22 when the flag signal corresponds
to 0. In the above arrangement, the hue signals and the chroma
saturation signals are output, which signals are obtained by
shifting the hue of only the signals within the range of the color
temperature correction (or within the range of those in the white
attributes) and by correcting the chroma saturation thereof.
[0068] The signals as output from the first and second selection
circuits 232 and 236 are, as described above, converted into the
color difference signals by the color difference conversion circuit
26, which signals are converted into the three primary colors
signals of R, G and B so as to be supplied to the display device
28. On the display device 28, the pictures as subjected to the
color temperature correction in an optimum manner according to the
input signals are displayed.
[0069] In the present embodiment, the color temperature correction
is performed on the signals in the white attributes of a given
luminance or more and a given chroma saturation or less, which
correction is performed on the hue, signals and the chroma
saturation signals respectively in the digitalized manner so that a
more highly precise color temperature correction is realized.
Further, the degree to which and the range within which the color
temperature is corrected is designated by the microcomputer, which
allows such degree and range to be adjusted in an arbitrary
manner.
[0070] FIG. 14 is a block diagram to show another embodiment of the
present invention, in which the same references are used for the
same elements as shown in FIG. 1 to avoid redundancy. FIG. 15 a
view to supplement FIG. 14. The difference in FIG. 14 with the
embodiment as shown in FIG. 1 lies in that a hue comparison circuit
131 is added to the structural elements of the color temperature
correction level detection circuit 17. The detection circuit with
the addition of this hue comparison circuit is referred to as 17',
which comparison circuit performs the operation to detect the
signals of a given hue among those in the white attributes of a
given luminance or more and a given chroma saturation or less so as
to exclude the signals of the given hue from the color temperature
correction. Hereafter, the arrangement thereof is described
below.
[0071] To one terminal of the hue comparison circuit 131, the
corrected hue signal as output from the hue correction circuit 20
is input, to the other terminal of which a hue set value as output
from the microcomputer and within the range as shown in hue 141 of
FIG. 15, for instance, is input. This hue set value is intended for
designating the range of hue to be excluded from the color
temperature correction, which value has two values representing the
initial end and the ultimate end thereof. The hue comparison
circuit 131 compares the corrected hue signal with the hue set
value and outputs 0 when the corrected hue signal is within those
two values while outputting 1 when it is out of those values (or
within the range as shown with slanting lines in FIG. 15). The
switching control circuit 173, to which the signals as output from
the luminance comparison circuit 171, the chroma saturation
comparison circuit 172 and the hue comparison circuit 131 are
input, performs the AND operation of those three signals so as to
output a flag signal for controlling the selection circuits 232 and
236. That is, when the luminance comparison circuit 171 detects a
signal of high luminance so as to output 1 and the chroma
saturation comparison circuit 172 detects a chroma saturation
signal of low chroma saturation so as to output 1 and the hue
comparison circuit 131 detects a signal out of the hue set values
so as to output 1, the switching control circuit 173 outputs a flag
signal corresponding to 1 to the selection circuits 232 and 236 so
that those circuits select the signals as output from the first and
second color temperature correction sections 231 and 235. On the
other hand, when the luminance comparison circuit 171 together with
the chroma saturation comparison circuit 172 output 1 while the hue
comparison circuit 131 detects a signal within the range of the hue
set values so as to output 0, the switching control circuit 173
outputs a flag signal corresponding to 0. Accordingly, because the
input signals are out of the range for the color temperature
correction, though those signals are of high luminance and an low
chroma saturation so as to belong to the white attributes, the
selection circuits 232 and 236 select the signals as output from
the hue correction circuit 20 and the chroma saturation correction
circuit 22, which signals are not subjected to the color
temperature correction.
[0072] The present embodiment allows the signals in the white
attributes within the range of the designated hue not to be
subjected to the color temperature correction. This leads to the
restriction of the range of hue on which the color temperature
correction is performed, which excludes the signals having a hue
that is undesirable to change from the correction of such hue.
Further, the range for the color temperature correction is
designated by the microcomputer, which range is adjustable in an
arbitrary manner.
[0073] FIG. 16 is a block diagram to show another embodiment of the
present invention. The difference in FIG. 16 with the embodiment as
shown in FIG. 1 lies in that a luminance correction circuit 151 is
provided therein.
[0074] In the following description, the same references are used
for the same structural elements as shown in FIG. 1 to avoid
redundancy.
[0075] The luminance correction circuit 151 is intended for
variably controlling the amplitude and direct current level of the
luminance signal as separated from the input picture signals by the
matrix conversion circuit 15, the detailed view of which circuit is
shown in FIG. 17. The luminance signal Y as output from the matrix
conversion circuit 15 is supplied to one input terminal of a black
expanding circuit 1606, to the other terminal of which circuit the
maximum set value of black expanding YBK and the gain coefficient
as set by the microcomputer 40 are supplied through an input
terminal 1602. The black expanding circuit 1606 variably controls
the amplitude of the luminance signal having the maximum set value
of black expanding YBK or less so as to output the same signal to
one terminal end of a white expanding circuit 1607, to the other
terminal end of which circuit the minimum set value of white
expanding YWT and the gain coefficient as set by the microcomputer
40 are supplied through an input terminal 1603. The white expanding
circuit 1607 variably controls the amplitude of the luminance
signal having the minimum set value YWT or more so as to supply the
same signal as subjected to the amplitude control to a
multiplication circuit 1608, which circuit multiplies the same
signal by a contrast control coefficient as input through a
terminal 1604 from the microcomputer 40 so as to variably control
the amplitude thereof or subject the same signal to contrast
control. A clipping circuit 1609, where the signal as output from
the multiplication circuit 1608 overflows, clips off the overflowed
portion thereof at the maximum value of 255 in 8 bits precision so
as to output the same signal, which signal is input to an addition
circuit 1610. The addition circuit 1610 adds the signal as input
thereto to a direct current (DC) value as input through a terminal
1605 from the microcomputer 40 so as to subject the same signal to
brightness control. A clipping circuit 1611, where the signal as
output from the addition circuit 1610 overflows, clips off the
overflowed portion thereof at the maximum value of 255 in 8 bits
precision. The signal as output from the clipping circuit 1611 is
output through a luminance output terminal 1614 to the inverse
matrix conversion circuit 27, the detection circuit 17 and the
color temperature correction circuit 23. Further, a maximum/minimum
level detection circuit 1612 detects the maximum and minimum level
of the luminance signal as input through a terminal 1601 before the
same signal is subjected to the luminance correction and outputs
the result to the microcomputer 40. The microcomputer 40 performs
the operation of the maximum set value of black expanding YBK and
the gain coefficient as input to the black expanding circuit 1606,
the minimum set value of white expanding YWT and the gain
coefficient as input to the white expanding circuit 1607, the
contrast control coefficient as input to the multiplication circuit
1608 and the direct current value as input to the addition circuit
1610 so as to determine the same values.
[0076] FIG. 18 is a view to give the supplemental explanation of
the operation of the luminance correction circuit 151 as mentioned
above and shows the input and output characteristics thereof. A
waveform 1701 of FIG. 18A shows the output characteristics of the
luminance signal as not subjected to the luminance correction, in
which the same signal as input from the terminal 1601 is output
without any correction made thereto. A waveform 1702 of FIG. 18B
shows the output luminance signal, the black and white portions of
which signal are expanded by the black and white expanding circuits
1606 and 1607. In the waveform 1702, the portion thereof as
processed by the black expanding circuit 1606 corresponds to the
continuous line of the set value YBK or less as subjected to the
gain adjustment while the portion thereof as processed by the white
expanding circuit 1607 corresponding to the continuous line of the
set value YWT or more as subjected to the gain adjustment. A
waveform 1703 of FIG. 18 C shows the input luminance signal, which
signal is subjected to the contrast control operation by the
multiplier 1608 and the clipping circuit 1609. In this drawing, for
the facility of understanding, the black and white expanding
characteristics thereof are not shown. A waveform 1704 of FIG. 18D
shows the output luminance signal where the same signal as shown
with the wave form 1701 is subjected to the brightness control
operation by the adder 1610 and the clipping circuit 1611. In this
drawing, the black and white expanding as well as the contrast
control characteristics thereof are not show for the facility of
understanding.
[0077] As described above, in the present embodiment, not only the
luminance control of the luminance signal (or contrast control) and
the direct current level control thereof (or brightness control)
are performed, but also the gray scale control of the high-level
luminance signal (or white expanding control) and that of the
low-level luminance signal (or black expanding control) are
performed, which allows the luminance signals vivid and rich in
gray scale (hereinafter, referred to as corrected luminance
signals) to be obtained. Further, the corrected luminance signals
are supplied to the detection circuit 17 and the color temperature
correction circuit 23 at the same time. Thus, the detection of the
color temperature correction area (or the area of the signals in
the white attributes) at the detection circuit 17 or 17' with the
corrected luminance signals in use correlates with the color
temperature correction at the color temperature correction circuit
23 with the same signals in use. Accordingly, the color temperature
correction is optimum also for the display device, the picture
quality of which becomes better with the luminance correction.
[0078] The signal processing circuit including the color
temperature correction thereof according to the present invention
is described above in details, which processing circuit is used for
a direct viewing type or a back projection television receiver as
well as for the display or monitoring device of computers. Further,
the display device incorporating this signal processing circuit
therein is available for not only a cathode ray tube, but also a
liquid crystal panel and a plasma display panel (PDP), for
instances. Further, according to the kinds of the display devices
with the variety of the characteristics such as color reproduction
and luminance saturation, it is preferable to alter the parameters
such as the minimum set value of luminance YB and the maximum set
value of chroma saturation ST relating to the hue and chroma
saturation correction, the detection of the area of the signals in
white color as well as the color temperature correction by means of
the microcomputer 40 where appropriate, which modification is also
included in the scope of the present invention. In any of the above
three embodiments, the color temperature correction is performed
subsequently to the hue correction and the chroma saturation
corrections, the order of which may be reversed. Further, the color
temperature correction may be performed without performing the hue
and chroma saturation corrections.
[0079] The present invention allows the hue and chroma saturation
of the picture signals of a given range to be corrected in an
optimum manner, which allows in particular the color temperature
correction of the signals in the white attribute of a given
luminance or more and a given chroma saturation or less to be
performed with high precision. Further, the color temperature
correction is not performed on the signals other than those in the
white attributes as designated, which allows the quality
deterioration of the pictures having the colors other than the
white attribute to abate.
* * * * *