U.S. patent number RE29,570 [Application Number 05/723,742] was granted by the patent office on 1978-03-07 for television system having aperture correction.
This patent grant is currently assigned to U.S. Phillips Corporation. Invention is credited to Hendrik Breimer, Sing Long Tan.
United States Patent |
RE29,570 |
Breimer , et al. |
March 7, 1978 |
Television system having aperture correction
Abstract
In a color television camera system of the type having camera
tubes for the production of red, green and blue color signals,
contour signals derived from only one of the color signals are
added to all of the color signals.
Inventors: |
Breimer; Hendrik (Eindhoven,
NL), Tan; Sing Long (Eindhoven, NL) |
Assignee: |
U.S. Phillips Corporation (New
York, NY)
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Family
ID: |
26644018 |
Appl.
No.: |
05/723,742 |
Filed: |
September 16, 1976 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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624944 |
Mar 21, 1967 |
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Reissue of: |
226432 |
Feb 15, 1972 |
03732360 |
May 8, 1973 |
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Foreign Application Priority Data
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Mar 26, 1966 [NL] |
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6604020 |
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Current U.S.
Class: |
348/253 |
Current CPC
Class: |
H04N
5/208 (20130101); H04N 9/09 (20130101) |
Current International
Class: |
H04N
9/09 (20060101); H04N 5/208 (20060101); H04N
009/535 () |
Field of
Search: |
;358/21,37,38,40,162,166 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1,512,352 |
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Jun 1969 |
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DT |
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1,156,841 |
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Nov 1963 |
|
DT |
|
753,313 |
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Jul 1956 |
|
UK |
|
Primary Examiner: Richardson; Robert L.
Attorney, Agent or Firm: Trifari; Frank R. Steinhauser; Carl
P.
Parent Case Text
CROSS REFERENCE
This case is a continuation of application Ser. No. 624,944 filed
on Mar. 21, 1967 and now abandoned, the priority of which is hereby
claimed.
The invention relates to a color television system comprising a
camera having three camera tubes for producing electric signals for
the red, blue and green color components respectively, of the image
to be taken by the camera. The image reproduced as a potential
image on the target plates of the camera tubes is converted by
lines and fields into red, green and blue color signals. The system
further comprises means for deriving a contour signal by comparing
one of the color signals with itself at more or less adjacent
points of the potential image.
In color television systems based on the principle of three primary
colors: red, green and blue, the light emanating from the scene to
be taken by the camera is split up into the three color components.
For each color component a potential image is produced on the
target plate of the relevant camera tube. By means of an electron
beam from the electron gun of the camera tube the camera tube
provides a color signal by scanning this image in lines and fields.
The three color signals can then be transmitted in known manner to
a color television receiver or monitor, so that the screen of the
display tube provides a color picture.
The following errors may appear in the picture on the screen of the
display tube:
First, in shadow-mask color television display tubes having three
electron guns the color picture is obtained by the superposition of
a red, green and blue image on the screen of the display tube. If
at the transmitter end coincidence errors appear, they will become
manifest in the form of time errors in the three color signals, so
that the three images produced by the color signals will not cover
each other completely. The display therefore also shows
superposition or coincidence errors, which are particularly
conspicuous at the transitions (in the color gradations) of the
image. These transitions correspond to the high frequencies in the
color signals. In order to eliminate the reproduction of the
superposition errors on the screen of a display tube, the high
frequencies of only one color signal has been transmitted, while
they are eliminated from the two other color signals. This may be
achieved by suppressing the high frequencies in two color signals
by filtering the color signals emanating from the camera, or by
causing the relevant camera tubes to provide only the low
frequencies of the two color signals.
However, this method does not eliminate the second error, which is
faded transitions in the picture on the screen of a display tube.
This error is produced by the small, but finite, cross-section of
the electron beam produced by the electron gun of the camera tube.
The size of the cross-section of the electron beam on the target
plate of the camera tube determines the possibility of transferring
transition information of the potential image on the target plate
to the signal provided by the camera tube. An electron beam of
small cross-section will transfer the transition information fairly
satisfactorily to the output signal of the camera tube. An electron
beam of larger cross-section, which comprises a current related to
two adjacent contrast values at the place of the transition in the
potential image, provides in a camera output signal which is an
average of the contrast values. Therefore, the transition of the
image is reproduced in faded fashion on the screen of the display
tube. It is obvious that a minimum cross-section of the electron
beam on the target plate of the camera tube is desired. However,
the minimum cross-section is determined by the maximum current
density of the electron beam, which determines the maximum transfer
of electric charge. A remedy for the lack of sharpness described
is, in general, found in aperture correction by a method also
employed in monochrome television. The influence of the size of the
cross-section of the electron beam on the reproduction of the
transition information of the image in the output signal of the
camera tube is corrected by deriving a contour signal from the
television signal, said contour signal being subsequently added to
the television signal. This method is described inter alia in the
article: "A Vertical Aperture Equalizer for Television" in the
"Journal of the SMPTE," June 1960, pages 395 - 401 of W. G. Gibson
and A. C. Schroder. The principle of aperture correction described
in this article may be applied to the line scanning (for example in
the horizontal direction) or to the field scan (for example in the
vertical direction) of the screen of the display tube. The contour
signal is obtained by the comparison of the color signals at more
or less adjacent points of the potential image by means of delay
lines. In order to obtain the contour signal in the line direction
the delay time is short, and in a direction at right angles to the
former the delay time is usually one line period or, sometimes,
about one field priod. By adding the contour signal to the color
signal, which would not exhibit sharp transitions in its
reproduction on the display screen, an aperture-corrected color
signal is obtained, This aperture-corrected color signal provides
sharp transitions and even over-compensation so that the
transitions are emphasized. This emphasis may be attributed to the
intensity and to the spatial extension of the contour signal on the
display screen.
In the color television system based on the principle of three
primary colors: red, green and blue, in which a camera having one
camera tube for each of the three colors it is known to apply
aperture-correction to each of the color signals. If an image
reproduced on the display screen exhibits superposition errors,
which are particularly conspicuous at the transitions and if
aperture-correction is applied to each of the three color signals
in the manner described above in order to further define the
contrasts, the superposition errors become even more manifest by
the aperture correction.
According to the invention an aperture-corrected picture is
obtained on the display screen without visible superposition errors
by applying only one color signal to said means for obtaining a
contour signal, so that a contour signal associated only with this
color signal is obtained. This contour signal is added to each of
the red, green and blue color signals separately, or to a sum of
them by means of a matrix network.
From the foregoing it will be seen that the invention is based on
the discovery that not only the superposition errors, but also the
fading transitions are visible only in the contours of the
displayed pictures. Therefore, an improved result is obtained by
leaving the high frequencies as they are (.[.since.]. .Iadd.though
.Iaddend.in this manner the fading transition is not corrected),
while only aperture-correction is derived from only one color
signal, so that both the superposition error and the fading
transition are remedied.
In principle it is not important which color signal is employed for
obtaining the contour signal. In practice it is found that the
color signal forming the greatest component of the brightness
signal composed of the three color signals provides the best
results. In systems having a brightness signal Y=0.30R+0.11B+0.59G
wherein R, G and B designate the red, green and blue color signals
respectively, the green color signal is chosen.
Claims
What is claimed is:
1. A color television system comprising means for producing
potential images corresponding to each of three color components of
an optical image and converting said potential images into color
component signals, means to derive a delayed signal from one of
said color component signals by comparing the color component
signal with itself at substantially adjacent points of the
potential image to thereby obtain a contour signal associated with
said color component signal, and means for adding said delayed
signal to all of said color component signals to sharpen
transitions therein.
2. A color television system as claimed in claim 1 wherein said
three color signals comprise red, blue, and green signals
respectively and the delayed signal is derived from the green color
signal.
3. A color television system as claimed in claim 1 wherein an
output signal comprises separate color signals and the delayed
signal is added to the individual color signals.
4. A color television system as claimed in claim 1 wherein said
adding means adds said color signals to form an output signal and
the delayed signal is added to the output signal comprising the sum
of the color signals.
5. A color television system as claimed in claim 1 wherein said
means for deriving a delayed signal comprises means for deriving
both a horizontal and a vertical aperture correction signal.
6. A device as claimed in claim 5 wherein said delay means further
comprises means for obviating said delay including means for
shifting the scan of the signal source from which the delay signal
is derived with respect to the scan of the remaining signal
sources. .Iadd. 7. A color television system comprising means for
producing potential images corresponding to each of three color
components of an optical image and converting said potential images
into color component signals, means to derive delayed horizontal
and vertical signals from only one of said color component signals
by comparing said one color component signal with itself at
substantially adjacent points of the potential image to thereby
obtain a contour signal associated with only said one component
signal, and means for adding said contour signal to an output
signal which included all of said color component signals to
sharpen image transitions therein.
.Iaddend..Iadd. 8. A color television system as claimed in claim 7
wherein said three color signals comprise red, blue and green
signals respectively, and the contour signal is derived from the
green color signal only. .Iaddend..Iadd. 9. A color television
system as claimed in claim 7 wherein said output signal comprises
separate color signals and the contour signal is added to each of
the individual color signals. .Iaddend. .Iadd. 10. A color
television system as claimed in claim 7 wherein said output signal
is a composite signal formed by adding said color signals in
predetermined portions and said contour signal is added to said
composite signal. .Iaddend..Iadd. 11. A color television system as
claimed in claim 7 wherein said delay means further comprises means
for obviating said delay including means for shifting the scan of
the signal source from which the delay signal is derived with
respect to the scan of remaining signal sources. .Iaddend.
Description
The invention will be described more fully by way of example with
reference to the following embodiments.
FIG. 1 shows a first embodiment of a color television system
according to the invention and
FIG. 2 shows a second embodiment.
Referring to FIG. 1, the camera tubes 1, 2 and 3 produce the color
signals green G, red R and blue B respectively. These color signals
are obtained by projecting, in a manner not shown in FIG. 1, the
particular color component of the image to be transmitted onto each
target plate of the camera tubes 1, 2 and 3, these three target
plates being simultaneously scanned by the respective electron
beams. The camera tubes 1, 2 and 3 supply the color signals, G, R
and B to conductors 4, 5 and 6 respectively. In connection with the
aforesaid choice of the color signal G for deriving the contour
signal, the conductor 4 applies the color signal G to the means 7
for deriving the contour signal. This contour signal is supplied by
means 7 to the conductor 8, whereas the conductor 9 conveys the
green color signal G. Then the contour signal of the green signal G
is applied through the conductor 8 and the color signals G, R and B
are applied through the conductors 9, 5 and 6 respectively to
summation devices 10, 11 and 12 and are added therein. From the
output of each summation device 10, 11 and 12 there can be derived
the aperture-corrected color signals G.sup.x, R.sup.x and B.sup.x.
It will be obvious that this diagram may include further elements
such as amplifiers, non-linear parts, filters and, if desired,
delay lines and so on. When gamma correction is applied to the
color television system, very good results are obtained on the
display screen by deriving the contour signal from a
non-gamma-corrected color signal and adding it subsequently to the
gamma-corrected color signal.
The elements shown in FIGS. 1 and 2 are designated by the same
reference numerals. The color signals G, R and B are applied
through the conductors 9, 5 and 6 respectively to a matrix network
13, in which the brightness signal Y is composed. The contour
signal derived by the means 7 from the green color signal G is
added through the conductor 8 in the summation device 14 to the
brightness signal Y. At the output of the summation device 14
appears the aperture-corrected brightness signal Y.sup.x.
The means 7 for deriving the contour signal are shown in detail in
FIG. 2. By means of storage tubes an integral aperture correction
may be obtained in the line direction and in the direction at right
angles thereto. If delay lines with separate aperture correction of
the vertical and horizontal directions are used, a diagram as shown
with the contour signal deriving means 7 in FIG. 2 is employed. The
contour signal in the vertical direction is provided by a means 15,
while a means 16 is used to generate a contour signal in the
horizontal direction so that through the summation device 17 the
total contour signal is applied to the conductor 8 and hence, to
the luminance signal by adder 14.
In detail, the vertical contour signal generator comprises delay
lines 20 and 21 each having a delay of about one line period, i.e.,
64 microseconds. The undelayed and twice delayed signals are added
together by adder 22 and the resultant sum subtracted in subtractor
23 from the once delayed signal. The result is a vertical contour
correction signal that is delayed by about 100 nanoseconds in delay
line 24, and then applied to one input of adder 17.
Similarly, the once delayed signal from vertical generator 15 is
twice delayed by about 100 nanoseconds each time by delay lines 26
and 27 in horizontal contour signal generator 16. The undelayed and
twice delayed signals are added in adder 28 and then subtracted
from the once delayed signal in subtractor 29. The resultant
horizontal contour correction signal is then applied to adder 17,
the output of which is said total contour signal. A delayed green
signal is applied through conductor 9 to said matrix 13.
It will be obvious that aperture correction may also be used in one
direction within the scope of the invention.
The color signals G through the conductor 9 will have a time delay,
because of delay lines 20 and 26 with respect to the color signals
R and B through the conductors 5 and 6. By means of a delay line in
each of the conductors 5 and 6 the short difference in time in the
horizontal direction and the time difference, for example, one line
period, in the vertical direction may be eliminated, since this
delay becomes manifest on the display screen in a shift of the
green field with respect to the red and blue fields. By using
interlacing in composing the picture on the display screen, this
shift at right angles to the horizontal direction is distinctly
visible. The shift of the fields may be obviated in a simple manner
by shifting the scan of the target plate by the electron beam in
the green camera tube 1 with respect to the scans in the red and
blue camera tubes 2 and 3 respectively. With interlacing this means
that in the vertical direction, the electron beam of the green
camera tube 1, scans the line (n+2) at the instant when in the red
and blue camera tubes 2 and 3 in the line n is scanned. Moreover,
the delay in the horizontal direction can be corrected by a similar
small shift in the horizontal direction over at least one image
point.
As stated above, the contour signal is derived from the green color
signal only by ay of example, since this signal provides the
greatest contribution to the brightness signal. The principle of
the invention with its advantages may be applied, thought with less
effective results, when the contour signal is derived from the red
or the blue color signal.
* * * * *