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

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.