JPS6324596B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a method for correcting details in a reproduced color image that deteriorates due to a part of subject brightness information included in the chroma component being lost because the chroma component is not completely reproduced in a high-resolution part of a color television signal. This relates to a correction method. In other words, in color television, the non-linearity of the electro-optical conversion characteristics of the color picture tube is corrected in advance on the image transmitting side before being transmitted, so the subject brightness information is added to the chrominance signal which is matrixed by applying non-linear correction to the three primary color images. Conventionally, when displaying a color television signal of the standard color television system on a receiver, due to the lack of brightness information in some of the brightness information as mentioned above, due to transmission band restrictions etc. Horizontal details in high-resolution areas are damaged,
In addition, in the case of YC separation using a comb filter or in the case of line-sequential transmission of chrominance components,
Only images with lost vertical detail could be reproduced. An object of the present invention is to provide a detail correction method that can improve two-dimensional details that have deteriorated in this way and reproduce high-quality color images. That is, the detail correction method of the present invention adds a luminance signal component related to the transmission frequency band for the chrominance signal of the color television signal to the luminance signal of the color television signal as a detail correction signal for the color television signal. It is characterized in that it is configured to transmit data. In the following, the invention will be explained in detail by way of example embodiments with reference to the drawings. In the conventional color television system, correction of the nonlinear operation of the color picture tube, that is, so-called gamma correction, is performed all at once on the image transmission side, and then the signal is encoded into a band-limited composite color television signal as a transmission signal. Then, transmit it. The brightness of the reproduced color image in this type of color television system, that is, the brightness Yd that reproduces the details of the reproduced color image, is given by equation (1) as follows. Now, if we apply nonlinear correction Γ to the three primary color image output image signals R, G, and B on the image sending side for gamma (γ), which represents the nonlinear characteristics of a color picture tube, then γ = 1/Γ = 2.2. , the three primary color input image signals Rc, Gc, and Bc of the color picture tube are derived from the luminance signal Y' and the chrominance signals R〓-Y', G〓-Y', B〓-Y' of the standard composite color television signal. Rc=[Y′+(R〓−Y′)] Gc=[Y′+(G〓−Y′)] Bc=[Y′+(B〓−Y′)] Considering the (γ) characteristic, the reproduction brightness Yd of the color picture tube is as follows. Yd=0.30Rc〓+0.59Gc〓+0.11Bc〓 =0.30[Y′+(R〓−Y′)]〓+0.59[Y′+(G〓−Y′)]〓+0.11[Y′ +(B〓−Y′)〕〓 =0.30 [(Y′)〓+γ・(R〓−Y′) ・(Y′)〓 ^-1 +γ・(γ−1)/2 ・(R〓−Y ′) ²・(Y′)〓 ^-2 +……] +0.59 [(Y′)+γ・(G〓−Y′) ・(Y′)〓 ⁻¹ +γ・(γ−1)/2 ・(G〓−Y′) ²・(Y′)〓 ⁻² +……] +0.11 [(Y′)〓+γ・(B〓−Y′) ・(Y′)〓 ⁻¹ +γ・(γ −1)/2 ・(B〓−Y′) ²・(Y′)〓 ⁻² +……] The third and subsequent terms in the above equation are sufficiently small and can be omitted, so Yd ≒(Y′)〓+γ・(Y′)〓 ^-1・(0.30R〓+0.59G〓+0.11B〓−Y′) +γ・(γ−1)/2・[0.30(R〓−Y′) ) ² +0.59(G〓−Y′) ² +0.11(B〓−Y′) ² 〕(Y′)〓 ^-2The luminance signal Y′ of the standard composite color television signal is as follows. is expressed in Y′=0.30R〓+0.59G〓+0.11B〓 Therefore, in the above equation, the second term becomes 0 and is expressed as follows. Yd＝(Y′)〓+γ・(γ−1)/2 ・(Y′)〓 ⁻²・[0.30(R〓−Y′) ² +0.59(G〓−Y′) ² +0.11( B〓−Y′) ² ]=(Y′)〓 +Ycm (1) Here, Ycm is the luminance signal component reproduced by the chrominance signal, and is expressed by the following equation (2). Ycm=γ・(γ−1)/2(Y′)〓 ^-2 [0.30(R ^1/ 〓
−Y′) ² +0.59(G ^1/ 〓−Y′)2+0.11(B ^1/ 〓−Y′) ²
] (2) This equation (2) becomes 0 when no coloring R=G=B, and the value becomes larger as the image becomes more saturated, has a larger deviation from achromatic color, and has higher brightness. . However, in the current NTSC color television, the chrominance signal is transmitted with a narrow band limit compared to the luminance signal Y', so the luminance signal component Ycm reproduced by the chrominance signal is It is significantly attenuated in the frequency range beyond the limited band, and as a result, the luminance component of the highly saturated image is attenuated at the horizontal spatial frequencies in the high frequency range, reducing horizontal details. In images reproduced after separation or images in which color signals are transmitted line-sequentially as in the SECAM method, the chrominance signal also attenuates in the vertical spatial frequency domain, so the luminance component also attenuates in the vertical spatial frequency domain. Vertical detail is also reduced. These reductions in detail in luminance signals will directly appear as deterioration in image quality, so in future high-definition television systems that are intended to construct extremely high-definition image systems, such reductions in details in luminance signals will be avoided. It must be minimized as much as possible. In order to eliminate this kind of detail reduction in the reproduced luminance signal, detail luminance signal components are added to the standard luminance signal Y′ in the frequency range where the chrominance components are not reproduced, and the reproduction is performed with detail correction on the screen of the color picture tube. The brightness Yd is
(3). Yd＝0.30(Y′+Δ)〓+0.59(Y′+Δ)γ +0.11(Y′+Δ)〓=Y (3) Here, Δ is the detail luminance signal component,
The following equation (4) is obtained. Δ=Y ^1/ 〓−Y′ (4) Furthermore, Y is a luminance signal representing the luminance of the subject, and is expressed by the following equation (5). Y=0.30R+0.59G+0.11B (5) Next, FIG. 1 shows an example of the circuit configuration of a color encoder that performs the above-described detail correction in the horizontal spatial frequency domain. In the illustrated configuration, reference numerals 0, 1, and 2 are color television cameras, from which three primary color image signals R, G, and B of a subject image are extracted. Each of the primary color image signals R, G, and B is raised to the 1/γ power by gamma correction circuits 3, 4, and 5, and then converted into a luminance signal Y' and chrominance components C ₁ and C ₂ by a matrix circuit 6 for transmission according to the standard method. is converted into The chrominance components C ₁ and C ₂ of the output of the matrix circuit 6 are NTSC
In the method, C ₁ = 1 [=-0.27 (B-Y') + 0.74 (P-Y')] C ₂ = Q [=0.41 (B-Y') + 0.48 (P-Y') ], and in the PAL and SCAM systems, C ₁ = V [= (RY')/1.14], C ₂ = U [= (B-Y')/2.03]. It is. These chrominance components
C ₁ and C ₂ are luminance signals by low-pass filters 7 and 8.
The frequency band is limited narrower than Y', and the signal is shaped into a composite signal by the color encoder 9 and sent out from the output terminal 10. Next, a configuration example of a detail correction system according to the present invention is shown in FIG. 1 surrounded by a dashed line. In the illustrated configuration, a color television camera 0,
A matrix circuit 1 that operates in the same way as the matrix circuit 6 receives each primary color image signal R, G, B from 1 and 2.
1, and a brightness signal Y representing the brightness of the subject is extracted using equation (5) above. This luminance signal Y is guided to the gamma correction circuit 12 and subjected to nonlinear correction to obtain a luminance signal component Y ^1/ 〓 expressed by the following equation (6). Y ^1/ 〓=(0.30R+0.59G+0.11B) ^1/ 〓 (6) This luminance signal component Y ^1/ 〓 is led to the mixer 13 and the standard method luminance signal Y' from the matrix circuit 6 is subtracted, Δ=( Y′ ^1/ 〓−Y′), the detail luminance signal component of equation (4) mentioned above is extracted, and further, the high-pass filter 14 extracts the chrominance signal component C ₁ , C ₂
Frequency components exceeding the cutoff frequencies of low-pass filters 7 and 8, which limit the frequency bands of , are extracted as high-frequency luminance signal components (Y′ ^1/ 〓−Y′) _H , and are guided to mixer 15 to be sent to the matrix circuit. It is added to the standard luminance signal Y' from 6. As a result of the above, some of the chrominance components of high-saturation color images are affected by the reduction in horizontal detail due to part of the subject brightness information included in the chrominance signal not being transmitted due to the limitation of the transmission frequency band of the chrominance signal. A compensated high-definition color television system can be constructed. It goes without saying that even if such detail correction is performed on the image sending side, the signal restoration process on the image receiving side is no different from the conventional one. In the standard composite color television signal, a carrier color signal is multiplexed into the high frequency region of the luminance signal, and in the NTSC system, these signals, that is, the luminance signal Y, are multiplexed in the vertical spatial frequency domain of the luminance image. The high frequency components of ' and the carrier color signal are frequency-division multiplexed, and a comb filter with a horizontal scanning frequency h period is used to separate these signals. In this case, since the chrominance component is filtered in the vertical direction, the details of the reproduced luminance in the vertical direction are reduced in the high chroma image area. FIG. 2a shows an example of a circuit configuration in which two-dimensional detail correction is performed on the image sending side in response to such a decrease in detail in the vertical direction. Each component 12, 13, 14 and 15 in the illustrated configuration is
This is a horizontal detail correction circuit that is exactly the same as that shown surrounded by a dashed line in FIG. Further, the output (Y ^1/ 〓−Y′) of the mixer 13 is filtered by a low-pass filter 21 having the same cutoff frequency as the transmission frequency band of the chrominance component, and a low frequency component is extracted.
Furthermore, it is guided to the mixer 15 through a comb filter 22 with a filtering characteristic shown by a solid line in FIG. It is added to the standard luminance signal Y' together with the high-frequency luminance signal component from the high-pass filter 14. Note that since the comb filter 22 has a one-line delay line, the standard luminance signal after one line is
A detail luminance signal related to Y' will be added. Therefore, the standard luminance signal from the matrix circuit 6 is passed through the delay correction system 23 for synchronizing the timing with the detail correction signal delayed by the filters 21 and 22, especially the filter 21.
Lead Y' to mixer 15. In order to match the timing of the chrominance signals C ₁ and C ₂ with the luminance signal Y', a similar delay correction system is installed between the low-pass filters 7 and 8 and the color encoder 9 in the configuration shown in Figure 1. insert. By doing so, the two-dimensional detail correction of the high chroma image is completely performed, and a composite color television signal can be obtained in which there is no loss of detail, which is a drawback of the conventional system. In addition, in the SECA method, two types of chrominance components are transmitted alternately for each line, and on the image sending side, the chrominance components of the missing lines are replenished by line memory and a color image is regenerated. , the signal processing process is shown in Table 1.

[Table] In Table 1, a is the original chrominance component, b
denotes a transmitted chrominance component, and c denotes a reproduced chrominance component. Through this signal processing process, a luminance error caused by an error component as shown in d, that is, a vertical detail loss occurs. In addition, in this case, the playback brightness Yd that appears on the screen
The errors of the three primary color input luminance signals of the color picture tube with respect to the three primary color luminance signals of the subject image are respectively ΔR, ΔG, and ΔB, and Yd=0.30 (R ^1/ 〓 + ΔR) 〓 +0.59 (G ^1/ 〓 + ΔG) 〓 It is expressed as +0.11 (B ^1/ 〓+ΔB)〓 (7), and when transformed, Yd＝0.30 [(R ^1/ 〓)〓 +(R ^1/ 〓)〓 ^-1・ΔR・γ] +0.59 [(G ^1/ 〓)〓 (G ^1/ 〓)〓 ^-1・ΔG・γ] +0.11 [(B ^1/ 〓)〓 +(B ^1/ 〓)〓 ^-1・ΔB・γ ] =0.30 (R+γ・ΔR・R ^1-1/ 〓) +0.59 (G+γ・ΔG・G ^1-1/ 〓) +0.11 (B+γ・ΔB・B ^1-1/ 〓) = (0.30R+0. 59G＋0.11B) +0.30・γ・ΔR／R ^1/ 〓・R +0.59・γ・ΔG／G ^1/ 〓・G +0.11・γ・ΔB／B ^1/ 〓・B =Y+0.30 (γ・ΔR/R ^1/ 〓)R +0.59(γ・ΔG/G ^1/ 〓)G +0.11(γ・ΔB/B ^1/ 〓)B (8) However, γ=2.2, and γ・ΔR／R ^1/ 〓・R＝γ・ΔR・R ^1-1/ 〓 =γ・ΔR・Rγ−1/γγ・ΔR・R ^1/2 (9) Therefore, the above equation (8) becomes YdY+0.30γ・ΔR・R ^1/2 +0.59γ・ΔG・G ^1/2 +0.11γ・ΔB・B ^1/2 (10) . Therefore, when reproduced on the color image display screen as a detail correction luminance signal (Y'+Δ)=(Y')=+γ・(Y')= ^-1・Δ, its luminance becomes (10) Detail correction can be performed by adding a detail luminance signal component Δ having the form expressed by the following equation to the standard luminance signal Y'. Therefore,
As the detail luminance signal component Δ: Δ=[0.30ΔR・R ^1/2 +0.59ΔG・G ^1/2 +0.11ΔB・B ^1/2 ]/Y′〓 ^-1 (0.30ΔR・R ^1/2 +0.59ΔG・G ^1/2 +0.11ΔB・B ^1/2 ]/Y′ [0.30ΔR・R ^1/ 〓+0.59ΔG・G ^1/ 〓 +0.11ΔB・B ^1/ 〓]/Y′ (11) as standard By subtracting it from the luminance signal Y' in advance, the luminance error component in equation (10) is canceled out on the display screen, and a nearly correct luminance image, that is, a luminance image with vertical details corrected, is reproduced. Figure 3 shows an example of a circuit configuration that performs such detail correction on the image sending side for SECAM color television signals.
The transmitted chrominance component signal shown in FIG.
03, the same primary color image signal as the reproduced three primary color image signal on the image receiving side is restored, and the subtraction circuits 104, 105,
106, each primary color component correction signal of ΔR, ΔG, and ΔB is obtained. In addition, each primary color image signal R′, G′,
B′ are the respective imaging output primary color image signals R,
Gamma correction is applied to G and B, and R ^1/ 〓,
G ^1/ 〓, B ^1/ 〓, multiplier circuits 107, 108,
109, each primary color correction signal component
0.30ΔR・R′, 0.59ΔG・G′ and 0.11ΔB・B′ are formed. Note that, as shown in equation (11) above, the first
The imaging output three primary color image signals R, G, and B of the color television cameras 0, 1, and 2 shown in the figure are directly supplied, and the output signals are 0.30ΔR・R ^1/2 and 0.59ΔG・G ^1/2 , respectively.
It can also be configured to obtain each primary color correction signal component of 0.11ΔB·B ^1/2 . These primary color correction signal components are added to a mixing circuit 110 and synthesized, and further, a division circuit 111 obtains a detail luminance signal component Δ expressed by equation (11). This detail luminance signal component Δ is a luminance correction signal component for correcting the luminance reproduced on the receiving screen when the chrominance signal is transmitted line-sequentially, and after being corrected by the mixer 112, A luminance signal for transmission is taken out from the output terminal 113. It goes without saying that this brightness correction signal component can be a signal in the same band as the transmission frequency band of the chrominance signal. As is clear from the above description, according to the present invention, various transmission processing processes of chrominance information in a color television system in which nonlinear characteristic correction exhibited by a color image reproduction display system is performed on the image transmission side, that is, (1) Band-limiting processing of chrominance signals (2) Signal processing that separates chrominance signals from luminance signals using a vertical spatial frequency filter (3) Two-dimensional reproduction of reproduced color images that is degraded due to line-sequential transmission of chrominance signals, etc. Since details can be corrected in advance through signal processing on the image transmission side, it will be useful when configuring a color television system that broadcasts high-definition color image information, such as in future high-definition television. Extremely advantageous. If such signal processing for detail correction is performed on the image transmission side, the required frequency band of the chrominance signal is reduced to the chromaticity spatial frequency characteristic of color vision, and a transmission signal form is created that reduces the chrominance signal spatial frequency characteristic in the vertical direction as well. Therefore, the two-dimensional frequency domain can be used efficiently to construct future high-definition television signal systems. Note that in the current system, it is necessary to allocate and transmit an extra frequency band that exceeds the visual chromaticity spatial frequency characteristic as a chrominance signal frequency band. Furthermore, in the future, when a color display device with linear electro-optical conversion characteristics such as a panel display is realized, the signal system to be applied will be different, but if the transmission signal system subjected to signal processing according to the present invention is used,
Correction circuits 3, 4, in the image transmission system shown in FIG.
By simply omitting step 5, there is no need to change any other configuration, and a color image with no change in quality can be received on the image receiving side. Therefore, future high-definition television systems can be constructed without being influenced by the characteristics of the reproduction display system.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a configuration example of a detail correction circuit according to the method of the present invention, FIGS.
The figure is a block diagram showing yet another example of the circuit configuration. 0, 1, 2...Color camera, 3, 4, 5, 12
... Gamma correction circuit, 6, 11... Matrix circuit,
7, 8, 21...Low pass filter, 9...Color encoder, 10...Output terminal, 13, 15...Mixer, 14...High pass filter, 22...Comb filter, 23...Delay correction circuit, 101...1 line Delay line, 102... Line switcher, 103... Matrix circuit, 104, 105, 106, 112...
subtraction circuit, 107, 108, 109... multiplication circuit,
110... Addition circuit, 111... Division circuit, 113...
Output terminal.

Claims (1)

[Scope of Claims] 1. A luminance signal component in a high frequency region related to band limitation of a transmission frequency band for a chrominance signal of a color television signal is used as a detail correction signal for the color television signal. In a detail correction method that is transmitted in addition to a luminance signal, the first luminance signal is obtained by gamma-correcting the signal obtained by supplying the three primary color signals constituting the color television signal to a first matrix circuit, and the three primary color signals Among the difference signals from the second luminance signal obtained by applying gamma correction to each signal and supplying the signals to the second matrix circuit, the frequency range other than that corresponding to the transmission frequency band for the chrominance signal of the color television signal A detail correction method characterized in that the signal component of is used as the detail correction signal. 2. In a color television system in which a vertical spatial frequency filter is used on the receiving side to separate a luminance signal and a chrominance signal, a vertical spatial frequency filter having characteristics complementary to the characteristics of the vertical spatial frequency filter is provided on the transmitting side. 2. The detail correction method according to claim 1, wherein the detail correction signal is formed from the difference signal using this vertical spatial frequency filter. 3. In a color television system in which chrominance signals are transmitted line-sequentially, the three primary color signals each subjected to gamma correction, the second luminance signal obtained from the second matrix circuit, and the chrominance signals of two adjacent scanning lines. are respectively supplied to the third matrix circuit and the new three primary color signals obtained, and the respective difference signals are multiplied by the three primary color signals each subjected to gamma correction, and then the signals are obtained by respectively supplying the same to the mixing circuit. 2. The detail correction method according to claim 1, wherein the detail correction signal is formed by dividing the second luminance signal.