Pure red color detection circuit and color compensation circuit using the same

Information

  • Patent Grant
  • RE38413
  • Patent Number
    RE38,413
  • Date Filed
    Friday, December 1, 2000
    23 years ago
  • Date Issued
    Tuesday, February 3, 2004
    20 years ago
  • US Classifications
    Field of Search
    • US
    • 348 649
    • 348 650
    • 348 679
    • 348 690
    • 348 703
    • 348 645
    • 348 646
    • 348 647
    • 348 648
    • 348 653
    • 348 654
    • 348 468
    • 348 630
    • 382 162
    • 382 167
    • 382 274
    • 358 518
    • 358 532
    • 358 448
    • 358 464
  • International Classifications
    • H04N964
Abstract
Red color saturation is increased and red color with higher purity can be reproduced by composing: a red color detection circuit 1 for detecting a red color signal having higher purity by inputting color differential signals (R-Y) and (B-Y) modulated by color subcarrier, subtracting the absolute value of the (B-Y) signal from the positive polarity component of the (R-Y) signal and removing the negative part of the subtracted signal; Y signal compensation block including: first gain controller 50b for controlling the output signal amplitude of red color detection circuit 1 and a subtracter 50a for subtracting the output signal of first gain controller 50b from a luminance signal Y; an (R-Y) signal compensation block including: second gain controller 51b for controlling the output signal amplitude of red color detection circuit 1 and an adder 51a for adding the output signal of second gain controller 51b and the input (R-Y) signal; and a (B-Y) signal compensation block including: third gain controller 52b for controlling the output signal amplitude of red color detection circuit 1, a polarity inverter 52c for inverting the output signal polarity of third gain controller 52b, a switch circuit 52d for selecting either input signal or output signal of polarity inverter 52c, a polarity discriminator 52e for discriminating the polarity of the input (B-Y) signal and controlling switch circuit 52d and an adder 52e for adding the output signal of switch circuit 52d and the input (B-Y) signal.
Description




FIELD OF THE INVENTION




The present invention relates to a pure red color detection circuit and a color compensation circuit compensating color differential signals by using it and emphasizing the red color.




BACKGROUND OF THE INVENTION




Television receivers having a high additional value have been developed according to their increased screen sizes and high quality color television receivers having a good red color reproducibility are desired.




Block diagrams of a red color detection circuit and a color compensation circuit in accordance with the prior art disclosed in Japanese Patent Laid-Open No.5-233667 are shown in

FIGS. 6 and 8

, respectively. The function of a red color detection circuit is explained below, referring to

FIGS. 6 and 7

.





FIG. 6

shows a block diagram of a red color detection circuit


101


of the prior art and

FIG. 7

shows signal waveforms at various points of red color detection circuit


101


. Red color detection circuit


101


includes an absolute value outputting circuit


101


b, a subtracter


101


c and a limiter


101


d. In

FIG. 7

, waveforms A and B are color differential signals (R-Y) and (B-Y), respectively which are input to red color detection circuit


101


and the color differential signal (R-Y) is behind the color differential signal (B-Y) by 90 degrees in phase. An absolute value B-Y is made from the input color differential signal (B-Y) at absolute value outputting circuit


101


b and is output (waveform C) and is input to subtracter


101


c. Subtracting the output of absolute value outputting circuit


101


b B-Y (waveform C) from color differential signal (R-Y) (waveform A) at subtracter


101


c (waveform D) and only a positive part is outputted from limiter


101


d (waveform E).




Because this signal exists near the phase of 90 degrees, the detected output is a signal corresponding to a red color in the input chrominance signal.




The function of a color compensation circuit of the prior art is explained below, referring to FIG.


8


. The color compensation circuit includes red color detection circuit


101


, an amplitude control circuit


102


for a color differential signal (R-Y) and another amplitude control circuit


103


for a color differential signal (B-Y). A color differential signal (R-Y) and red color detected signal (waveform E) in

FIG. 7

output from red color detection circuit


101


are supplied to amplitude control circuit


102


and the color differential signal (R-Y) is controlled by the red color detected signal so that the amplitude decreases. Also a color differential signal (B-Y) and the red color detected signal output from red color detection circuit


101


are supplied to amplitude control circuit


103


and also the color differential signal (B-Y) is controlled by the red color detected signal so that the amplitude decreases. Thus, suppressing a signal having a large red component prevents red color from saturation.




This circuit, however, aims to prevent red color saturation and a different kind of apparatus is necessary for improving red color reproducibility which is intended in the present invention. The present invention detects a signal closer to a pure red color in a red color detection circuit and decreases a Y/C ratio, emphasizes a red color without saturating the red color and as a result, improves red color reproducibility by decreasing the luminance signal Y by the red color detection signal and bringing a color phase of the chrominance signal C closer to a red color by the red color detection signal in the color compensation circuit.




SUMMARY OF THE INVENTION




A pure red color detection circuit of the present invention slices a subcarrier modulated color differential signal (R-Y) at a designated level at a slice circuit, generates an absolute value signal of a subcarrier modulated color differential signal (B-Y) at an absolute value outputting circuit, subtracts the absolute value B-Y from the sliced signal at a subtracter, takes out only a positive part of the subtracted signal at a limiter and outputs. The output signal is a signal having a narrow phase range near 90 degrees in the chrominance signal and as a result, a pure red color is detected.




A color compensation circuit of the present invention includes the above mentioned pure red color detection circuit, a Y signal compensation block, an (R-Y) signal compensation block and a (B-Y) signal compensation block and decreases a Y/C ratio, makes the chrominance signal containing a red color signal higher than a designated level close to a pure red color, emphasizes the red color without saturation and can improve red color reproducibility by outputting a luminance signal Y′ which is made by subtracting the pure red signal detected at the pure red detection circuit from the input luminance signal Y, at the Y signal compensation block, outputting a color differential signal (R-Y)′ which is made by adding the pure red signal detected at the pure red color detection circuit to the input (R-Y) signal, at the (R-Y) signal compensation block and outputting a color differential signal (B-Y)′ which is made by subtracting the pure red signal detected at the pure red detection circuit from the input color differential signal (B-Y), at the (B-Y) signal compensation block.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a block diagram of a pure red color detection circuit in accordance with an exemplary embodiment of the present invention.





FIG. 2

shows waveforms at various points in a pure red color detection circuit in accordance with an exemplary embodiment of the present invention.





FIG. 3

is a block diagram of a color compensation circuit in accordance with an exemplary embodiment of the present invention.





FIG. 4

shows color phase coordinates explaining how to rotate a vector of a chrominance signal close to an (R-Y) axis at a color compensation circuit in accordance with an exemplary embodiment of the present invention.





FIG. 4A

shows color phase coordinates when the vector of a chrominance signal C is in a first quadrant.





FIG. 4B

shows color phase coordinates when the vector of a chrominance signal C is in a second quadrant.





FIG. 5

is another block diagram of a (B-Y) signal compensating block of a color compensation circuit in accordance with an exemplary embodiment of the present invention.





FIG. 6

is a block diagram of a red color detection circuit in accordance with the prior art.





FIG. 7

shows waveforms at various points in a red color detection circuit in accordance with the prior art.





FIG. 8

is a block diagram of a color compensation circuit in accordance with the prior art.











PREFERRED EMBODIMENTS OF THE INVENTION




(First exemplary embodiment)




The function of a pure red color detection circuit is explained below, referring to

FIGS. 1 and 2

. All the signals treated in the exemplary embodiments are digital data. A block diagram of a pure red color detection circuit of the present invention is shown in FIG.


1


and waveforms at various points in the pure red color detection circuit are expressed by analog signals as shown in FIG.


2


. The pure red color detection circuit


1


includes a slice circuit


1


a, an absolute value outputting circuit


1


b, a subtracter


1


c and a limiter


1


d. In

FIG. 2

, waveforms A and B are color differential signals (R-Y) and (B-Y) supplied to the pure red detection circuit, respectively and the color differential signal (R-Y) is delayed from the color differential signal (B-Y) by 90 degrees in phase. The color differential signal (R-Y) is sliced at sliced levels +/−Ls at slice circuit


1


a and a signal over the slice levels is output (waveform C in

FIG. 2

) and is supplied to a subtracter


1


c. An absolute value B-Y is generated from the color differential signal (B-Y) at absolute value outputting circuit


1


b (waveform D) and is supplied to subtracter


1


c. The output of absolute value outputting circuit


1


b (waveform D) is subtracted from the output of slice circuit


1


a (waveform C) at subtracter


1


c (waveform E) and only a positive part of the subtracted signal it output from limiter


1


d (waveform F). The detected signal is narrower in width in the present invention than that of the prior art because of being added with a slice circuit (t indicated in waveform F,

FIG. 2

of the present invention compared with t′ indicated in waveform F,

FIG. 7

of the prior art), and a signal concentrated near 90 degrees, expressing by a color phase, that is close to the (R-Y) axis is detected. As a result, a signal close to a pure red color contained in the input chrominance signal is detected.




Thus, according to the present invention, a purer red color can be detected by outputting a red color detection signal only from a chrominance signal including a red color signal higher than a designated slice level.




(Second exemplary embodiment)




The function of a color compensation circuit of the present invention is explained below, referring to a block diagram shown in FIG.


3


. The color compensation circuit includes a pure red color detection circuit


1


, a Y signal compensation block


50


, an (R-Y) signal compensation block


51


and a (B-Y) signal compensation block


52


. Y signal compensation block


50


includes a subtracter


50


a and a gain controller


50


b. (R-Y) signal compensation block


51


includes an adder


51


a and a gain controller


51


b. (B-Y) signal compensation block


52


includes an adder


52


a, a gain controller


52


b, a polarity inverter


52


c, signal selection circuit


52


d and a polarity discriminater


52


e. Pure red color detection circuit


1


are supplied with color differential signals (R-Y) and (B-Y) and outputs a pure red detection signal R. The pure red color detection signal R is supplied to Y signal compensation block


50


and (R-Y) signal compensation block


51


.




Pure red color detection signal R supplied to Y signal compensation block


50


is gain-controlled at gain controller


50


c and is supplied to subtracter


50


a. Subtracter


50


a subtracts the gain-controlled pure red color detected signal R′ from the luminance signal Y and outputs the result. The output signal is a luminance signal Y′, the luminance of which corresponding to the pure red color part is somewhat suppressed.




Pure red color detection signal R supplied to (R-Y) signal compensation block


51


is gain-controlled at gain controller


51


c and is supplied to adder


51


a. Adder


51


a adds the gain-controlled pure red color detected signal R′ to the color differential signal (R-Y) and outputs the result. As shown in

FIG. 4

, adder


51


a outputs a red color differential signal (R-Y)′ with an increased amplitude, when the chrominance signal C is in a first quadrant (

FIG. 4A

) or in a second quadrant (FIG.


4


B).




The output R of pure red color detection circuit


1


and the color differential signal (B-Y) are supplied to (B-Y) signal compensation block


52


. The output R of the pure red color detection circuit


1


is gain-controlled in gain controller


52


b (B′) and its polarity is inverted by polarity inverter


52


c (−B′). Both signals before and after polarity inversion are supplied to a signal selection circuit


52


d. The other input color differential signal (B-Y) of (B-Y) signal compensation block


52


is discriminated its polarity by polarity discriminater


52


e and switches the connection in signal selection circuit


52


d. Signal selection circuit


52


d is controlled to select the output of polarity inverter


52


c (connect to the upper terminal of the switch in

FIG. 3

) when polarity discriminater


52


e judges that the input color differential signal (B-Y) is positive and to select the input of polarity inverter


52


c (connect to the lower terminal of the switch in

FIG. 3

) when polarity discriminater


52


e judges that the input (B-Y) signal is negative. Adder


52


a adds the positive or negative pure red color detected signal (B′ or −B′) of signal selection circuit


52


d to the input color differential signal (B-Y) and outputs the added signal. As shown in

FIG. 4

, when the chrominance signal C is in a first quadrant (FIG.


4


A), in other words the color differential (B-Y) signal is positive, signal selection circuit


52


d selects the output of polarity inverter


52


c and (B-Y) signal compensation block


52


outputs the value corresponding to {(B-Y)−B′}. As a result, the amplitude of the (B-Y) signal decreases. When the chrominance signal C is in a second quadrant (FIG.


4


B), in other words the color differential signal (B-Y) is negative, signal selection circuit


52


d selects the input of polarity inverter


52


c and (B-Y) signal compensation block


52


outputs the value corresponding to −{(B-Y)−B′}. As a result the amplitude of the (B-Y) signal also decreases.




As shown in

FIG. 4

, when the chrominance signal is in a first quadrant or in a second quadrant, the synthesized chrominance signal C′ rotates to be close to the (R-Y) axis in phase, because the (R-Y) component increases and (B-Y) component decreases by using the pure red color detected signal. The Y/C ratio is decreased, because the level of the luminance signal Y is lowered by the pure red color detected signal for a red part. By lowering the luminance level for a red part and rotating, the phase of a color close to red towards the (R-Y) axis is realized. As a result, yellowish color included in red is eliminated and a red color with high purity is reproduced.




A block diagram of another composition of a (B-Y) signal compensation block included in a color compensation circuit is shown in FIG.


5


. The (B-Y) signal compensation block


152


includes an adder


152


a, a gain controller


152


b, a multiplier


152


f and a polarity discriminator


152


e.




The output R of pure red color detection circuit


1


and a (B-Y) signal are inputted to (B-Y) signal compensation block


152


. The output of pure red color detection circuit


1


R is gain-controlled in gain controller


152


b (B′) and is supplied to multiplier


152


f. On the other hand, the (B-Y) signal is discriminated its polarity in polarity discriminater


152


e and if the (B-Y) signal is positive, a signal corresponding to −1 is outputted and if it is negative, a signal corresponding to +1 is outputted. The signals are supplied to multiplier


152


f. The output B′ of gain controller


152


b is multiplied by the output of polarity discriminater


152


e, i.e. the value corresponding to 1 in multiplier


152


f and the multiplied output is supplied to adder


152


a. Therefore, multiplier


152


f works as a combination of a polarity inverter (


52


c in

FIG. 3

) and a signal selection circuit (


52


d in FIG.


3


). Adder


152


a adds the output of multiplier


152


f to the other input (B-Y). Because multiplier


152


f works as a combination of a polarity inverter (


52


c in

FIG. 3

) and a signal selection circuit (


52


d in FIG.


3


), the (B-Y) signal compensation block


152


also has the same function as the above mentioned (B-Y) signal compensation block


52


.




In the color phase coordinates shown in

FIG. 4

, if the chrominance signal is in a first quadrant (FIG.


4


A), multiplier


152


f outputs the value corresponding to −B′ and (B-Y) signal compensation block


152


outputs the value corresponding to {(B-Y)−B′} so that the amplitude decreases. If the chrominance signal C is in a second quadrant (FIG.


4


B), multiplier


152


f outputs the value corresponding to +B′ and (B-Y) signal compensation block


152


outputs the value corresponding to −{(B-Y)−B′} so that the amplitude also decreases.




INDUSTRIAL APPLICABILITY




Thus, according to the present invention, in the pure red color detection circuit, a pure red color signal can be detected by slicing a color differential signal (R-Y) at a designated slice level, subtracting an absolute value of the color differential signal (B-Y) from the sliced (R-Y) signal and taking out only the positive part of the subtracted signal.




In a color compensation circuit using the pure red color detection circuit, the chrominance signal C can be rotated closer to the (R-Y) axis. This improvement is performed by decreasing the level of the high saturated red part and decreasing a Y/C ratio for a luminance signal Y, and adding the pure red detection signal and increasing the amplitude for the color differential signal (R-Y) and decreasing the amplitude by the pure red detection signal for the color differential signal (B-Y).




In a color television receiver using the above mentioned circuit, saturation is prevented for a strong red part, yellowish color contained in red is eliminated, highly pure red is reproduced and a picture with excellent color reproducibility can be obtained.




REFERENCE NUMERALS






1


. . . red color detection circuit






1


a . . . slice circuit






1


b . . . absolute value outputting circuit






1


c . . . subtracter






1


d . . . limiter






50


. . . Y signal compensation block






51


. . . (R-Y) signal compensation block






52


. . . (B-Y) signal compensation block






50


a . . . subtracter






51


a,


52


a,


152


a . . . adder






50


b,


51


b,


52


b . . . gain controller






52


c . . . polarity inverter






52


d . . . signal selection circuit






52


e,


152


e . . . polarity discrimination circuit






52


f,


152


f . . . multiplier



Claims
  • 1. A pure red color detection circuit comprising:a slice meanscircuit for inputtingreceiving a color demodulated color-difference signal (R-Y) and for extractingoutputting an (R-Y) signal component at a slice level (Ls); absolute value means for inputting a color demodulated color-difference signal (B-Y) and for outputting an absolute value component of said inputted color-difference signal (B-Y); subtraction means for subtracting the absolute value component of the (B-Y) signal output from said absolute value means , from the (R-Y) signal sliced at said slice level (Ls) and output from said slice means ; and limited meansa limiter for removing a negative component of thea signal output from said subtraction means and for outputting a red color component having an (R-Y) signal component in a first andor a second quadrantsin a Cartesian plane.
  • 2. A color compensation circuit comprising:red color detection means for detecting a red component, using color difference signals (R-Y) and (B-Y); and Y signal compensation means for compensating a Y signal, using thewhich receives an output signal of said red color detection means; and wherein said Y signal compensation means comprises: first gain control means for decreasing thean output signal amplitude of said red color detection means; and second subtraction means for subtracting thean output signal of said first gain control means from the Y signal.
  • 3. A color compensation circuit comprising:red color detection means for detecting a red component, using color difference signals (R-Y) and (B-Y); and (R-Y) signal compensation means for compensating said (R-Y) signal, using thewhich receives an output signal of said red color detection means; and wherein said (R-Y) signal compensation means comprises: second gain control means for controlling thean output signal amplitude of said red color detection means; and first addition means for adding said (R-Y) signal and thean output signal of said second gain control means.
  • 4. A color compensation circuit comprising:pure red color detection means for inputtingreceiving color demodulated (R-Y) and (B-Y) signalsignals and detecting a red color from the (R-Y) and (B-Y) signals; gain control means for controlling gain of a red detectingdetection signal detected asat said pure red color detection means and outputted from said pure red color detection means; and addition means inputtingfor receiving an output signal from said gain control means and the (B-Y) signal, and outputting a compensated (B-Y) signal as a (B-Y)′ signal.
  • 5. A color compensation circuit comprising:pure red color detection means for inputtingreceiving color demodulated (R-Y) and (B-Y) signals and for detecting a red color from the (R-Y) and (B-Y) signals; first and second gain control means for controlling gain of a red detectingdetection signal detected at said pure red color detection means and outputted from said pure red color detection means; first addition means for inputting thereceiving an output signal from said firsta third gain control means and the (B-Y) signal, and for outputting a compensated (B-Y) signal as a (B-Y)′ signal; and second addition means for inputting thereceiving an output signal from said second gain control means and the (R-Y) signal, and for outputting a compensated (R-Y) signal as a (R-Y)′ signal.
  • 6. A color compensation circuit comprising:pure red color detectingdetection means for detecting a red color component, using color-difference signals (R-Y) and (B-Y); first, second and third gain control means for independently controlling gain of a signal detected at said pure red color detection means; secondfirst subtraction means for inputting thereceiving a signal output from said first gain control means and a Y signal, and for subtracting the signal output from said second first gain control means from said Y signal; first addition means inputting thefor receiving a signal output from said second gain control means and the (R-Y) signal; andsecond addition means inputting thefor receiving a signal output from said third gain control means and the (B-Y) signal; andwherein said pure red color detection means includes: slice means for inputtingreceiving a color demodulated color-difference signal (R-Y) and for extractingoutputting an (R-Y) signal component at a slice level; absolute value means for inputting a color demodulated color-difference signal (B-Y) and for outputting an absolute value component of said inputted color-difference signal (B-Y); firstsecond subtraction means for subtracting the absolute value component of the (B-Y) signal output from said absolute value means, from the (R-Y) signal at said slide level and output from said slice means ; and limiter means for removing a negative component of thea signal output from said second subtraction means and for outputting a red color component having an (R-Y) signal component in first and second quadrants.
  • 7. A color compensation circuit comprising:red color detection means for detecting a red component, using color differential signals (R-Y) and (B-Y); and (B-Y) signal compensation means for decreasing an absolute value of said color differential signal (B-Y), using thean output signal of said red color detection means,; wherein said (B-Y) signal compensation means includes: third gain control means for decreasing the amplitude of thean output signal of said red color detection means; polarity discrimination means for judging an output signal polarity of said color difference signal (B-Y); polarity inverting means for inverting the outputa signal polarity of an output signal from said third gain control means; signal selection means for outputting an output signal of said polarity inverting means if said color differential signal (B-Y) has a positive polarity and outputting an output signal of said third gain control means if said color difference signal (B-Y) has a negative polarity; and third addition means for adding thean output signal of said signal selection means and said color difference signal (B-Y).
  • 8. A color compensation circuit comprising:red color detection means for detecting a red component, using color differential signals (R-Y) and (B-Y); and (B-Y) signal compensation means for decreasing an absolute value of said color differential signal (B-Y), using thean output signal of said red color detection means,; wherein said (B-Y) signal compensation means comprises: third gain control means for decreasing thean amplitude of the output signal of said red color detection means; polarity discrimination means for judging thea polarity of said color difference signal (B-Y) and outputting a +1 if said color difference signal (B-Y) has a negative polarity or a −1 signalif said color difference signal (B-Y) has a positive polarity; multiplication means for multiplying thean output signal of said third gain control means by thean output signal of said polarity discrimination means; and third addition means for adding thean output signal of said multiplication means and said (B-Y) signal.
  • 9. A color compensation circuit as defined in claim 2, further including a purewherein said red color detection circuit whichmeans comprises:slice means for slicing a color difference signal (R-Y) with a designated slice level and outputting a sliced signal; absolute value means for outputting an absolute value of a color difference signal (B-Y); firstsecond subtraction means for subtracting thean output signal of said absolute value means from the outputsliced signal of said slice means; and limiter means for removing a negative polarity part of thean output signal of said firstsecond subtraction means.
  • 10. A color compensation circuit as defined in claim 3, further including a purewherein said red color detection circuit whichmeans comprises:slice means for slicing a color difference signal (R-Y) with a designated slice level and outputting a sliced signal; absolute value means for outputting an absolute value of a color difference signal (B-Y); first subtraction means for subtracting thean output signal of said absolute value means from the outputsliced signal of said slice means; and limiter means for removing a negative polarity part of thean output signal of said first subtraction means.
  • 11. A color compensation circuit as defined in claim 4, further including a purewherein said red color detection circuit whichmeans comprises:slice means for slicing a color differential signal (R-Y) with a designated slice level and outputting a sliced signal; absolute value means for outputting an absolute value of a color difference signal (B-Y); first subtraction means for subtracting thean output signal of said absolute value means from the outputsliced signal of said slice means; and limiter means for removing a negative polarity part of thean output signal of said first subtraction means.
Priority Claims (1)
Number Date Country Kind
9-051339 Mar 1997 JP
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Divisions (1)
Number Date Country
Parent 09/035684 Mar 1998 US
Child 09/727884 US
Reissues (1)
Number Date Country
Parent 09/035684 Mar 1998 US
Child 09/727884 US