JPH0418512B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to gamma correction in color television broadcasting.

<Prior art> In color television broadcasting, if the luminance signal Y and the color signals I and Q created based on the three primary color signals R, G, and B are sent as they are, they will be distorted due to the nonlinearity of the picture tube. Since colors cannot be faithfully reproduced, a gamma-corrected signal is broadcast. The current gamma correction is Y′=0.30R ^1/ 〓+0.59G ^1/ 〓+0.11B ^1/ 〓 (1) I′=0.60R ^1/ 〓−0.28G ^1/ 〓−0.32B ^1/ 〓 ( 2) Q′=0.21R ^1/ 〓−0.52G ^1/ 〓−0.31B ^1/ 〓 This is done according to (3). However, with this correction method, the high-frequency reproducibility of the luminance signal deteriorates when the color is highly saturated.

One way to prevent the brightness resolution from deteriorating with highly saturated colors is to use Y ^1/ 〓 = (0.30R + 0.59G + 0.11B) ^1/ 〓 (4) instead of the brightness signal using equation (1), ( Broadcasting together with color signals of formulas 2) and (3) is shown in "Broadcasting Technology Series Color Television," edited by the Japan Broadcasting Corporation, pages 251 to 253. According to this proposal, the brightness on the receiver screen is based on the original brightness signal Y.
Since it is proportional to , a monochrome receiver can reproduce the desired brightness, and a color receiver can also reproduce the correct brightness in the high range.

<Problems to be Solved by the Invention> As described above, in the current gamma correction method, the reproducibility of the luminance signal in the high range deteriorates when the color is highly saturated. Furthermore, when using the above-mentioned proposal to solve this problem, the color reproducibility in the low range of the luminance signal deteriorates, and in order to reproduce the luminance correctly, it is necessary to As stated in the line, input Y ^1/ 〓 to the receiver when below 0.5MHz.
There is the inconvenience of having to provide a circuit for converting to Y'.

<Means for solving the problem> In the present invention, the luminance signal Y ^1/ 〓 (second luminance signal) according to equation (4) is calculated using the frequency region existing between 0.5 MHz and 1.5 MHz as the boundary. High frequency component and (1)
A brightness signal for broadcasting (fourth brightness signal) is created by combining the low-frequency component of the brightness signal Y' (third brightness signal) according to the formula.

The luminance signal Y ^1/ 〓 is from the three primary color signals R, G, B (4)
Uses a matrix that obtains the component in parentheses (first luminance signal Y) on the right side of the equation, and a gamma correction circuit that performs gamma correction on the luminance signal Y obtained by this matrix and converts it into a luminance signal Y ^1/ 〓 and create it.

The luminance signal Y' is generated from a gamma correction circuit that gamma-corrects the three primary color signals R, G, and B, respectively, and the three primary color signals R ^1/ 〓, G ^1/ 〓, B ^1/ 〓 that have undergone the gamma correction.
It is created using a matrix that performs calculations according to formula (1). Note that in this matrix, color signals I' and Q' according to equations (2) and (3) are also created at the same time.

A high-pass filter is used to extract high-frequency components from the boundary frequency region of the luminance signal Y ^1/ 〓.
A low-pass filter is used to extract components lower than the boundary frequency region of Y′. Then, both luminance signals that have passed through the filters are combined in an adder (synthesizing circuit) to form a broadcasting intensity signal (fourth luminance signal), which is then combined with the color signal for broadcasting color television. used to create a signal.

The boundary frequency region refers to a range from 0.5 MHz, which is the upper limit of the color signal Q' component, to 1.5 MHz, which is the upper limit of the color signal I' component. A fixed boundary frequency f (for example, 1.0MHz) is set within this region, and this boundary frequency f
In the following, the luminance signal Y' will be used, and above the boundary frequency f, the luminance signal Y ^1/ 〓 can be used.

However, the boundary frequency f is continuously changed depending on the ratio of the color signal I' component and Q' component, and when the I' component is large, it takes a value close to 1.5 MHz, and when the Q' component is large, it takes a value close to 1.5 MHz. It is desirable to have a value close to .

Furthermore, within the boundary frequency region of 0.5 to 1.5 MHz, a mixed signal of Y' and Y ^1/ 〓 may be used as the luminance signal. This mixing ratio may be a fixed ratio such as 1:1, but when the I' component is large, the luminance signal Y' content is high, and when the Q' component is large, the luminance signal Y ^1/ 〓 content is high. It is desirable to change the rate continuously so that the rate increases.

Note that when determining these boundary frequencies f and mixing ratios, instead of using the gamma-corrected color signals I' and Q' as described above, the non-gamma-corrected color signals I and Q may be used. .

<Function> In the above explanation, since the second luminance signal Y ^1/ 〓 according to equation (4) is transmitted as the high frequency portion of the luminance signal that is not related to the color signal, the receiving side cannot reproduce the luminance in the high frequency range. It can eliminate sexual deterioration. As for the low-frequency portion of the luminance signal affected by the color signals I and Q, the third luminance signal Y' according to equation (1) is transmitted, so there is no problem with color reproducibility as in the current broadcasting system. I won't come. Moreover, by performing such transmission, an improved image can be obtained on the receiving side without using a special receiver.

Also, when the I component of the color signal is large, the luminance signal
The components below 1.5MHz are related to color reproduction, and when there are many Q components, the components below 0.5MHz of the luminance signal are related to color reproduction, so the second and third luminance signals
Adjust the boundary frequency f of Y ^1/ 〓 and Y' by the ratio of color signals I and Q, or adjust the mixing ratio of the second and third luminance signals in the boundary frequency region between 0.5 and 1.5 MHz. By adjusting the ratio of the color signals I and Q, the reproducibility in high frequencies, that is, the resolution, can be improved to the maximum without impairing the color reproducibility at all.

<Embodiment> In FIG. 1, 1 is a color camera which outputs video signals R, G, and B of three primary colors. These outputs are divided into a luminance signal Y and a color signal I in matrix 2.
and Q, and the luminance signal is sent to the gamma correction circuit 3.
is converted into a luminance signal Y ^1/ 〓 according to equation (4).
Furthermore, the video signals R, G, and B are processed by gamma correction circuits 4, 5, and 6, respectively, and become gamma-corrected video signals R ^1/ 〓, G ^1/ 〓, B ^1/ 〓, which are sent to the matrix 7. is introduced into the luminance signal according to equation (1).
Y' and color signals I' and Q' according to equations (2) and (3).

8 is a filter that passes the signal above the boundary frequency f, which filters the luminance signal Y ^1/ 〓 outputted by the gamma correction circuit 3 and guides it to the adder 10, and 9 is a filter that passes the signal below the border frequency f. , the luminance signal Y' output from the matrix 7 is filtered and guided to the adder 10.
The output of the adder 10 is guided to the NTSC encoder 14 through the 4.2MHz low-pass filter 11, and the color signals I' and Q' output by the matrix 7 are respectively
It is guided to an NTSC encoder 14 through a 1.5 MHz low pass filter 12 and a 0.5 MHz low pass filter 13.

Reference numeral 15 denotes a control circuit for the filter cutoff frequency f, which controls the filter cutoff frequency f according to the ratio between the I component and the Q component of the color signal outputted by the matrix 2, for example, with characteristics as shown in FIG. That is, the cutoff frequency f of the filters 8 and 9 is
As shown in FIG. 5, when K=I/(I+Q) is 0, the frequency is set to 0.5 MHz, when K=1, the frequency is set to 1.5 MHz, and in between, it changes continuously depending on the value of K. The filters 8 and 9 are configured using current-controlled inductors and voltage-controlled capacitors so that the cutoff frequency f can be controlled in this manner.

In the above-mentioned device, the luminance signals added by the adder 10 below the frequency f follow equation (1), and above the frequency f follow equation (4).
The color television broadcast signal output from the NTSC encoder and broadcast includes such a luminance signal and a color signal according to equations (2) and (3).
Therefore, when this broadcast signal is received, resolution is improved by using the luminance signal of equation (4), and color reproducibility is faithfully achieved by using the luminance signal of equation (1). . Moreover, since the boundary frequency is adjusted according to the contents of the I component and Q component of the color signal, resolution can be improved to the maximum without impairing color reproducibility.

In the embodiment shown in FIG. 3, digital filters are used as filters 8 and 9. The color signal I component and Q component obtained from the matrix 2 are digitized by AD converters 18 and 19 after passing through low-pass filters 16 and 17 with cut-off frequencies of 1.5 MHz and 0.5 MHz, respectively. The filter control circuit 15 calculates the value of K=I/(I+Q), finds the parameter value f corresponding to the calculated value K using the lookup table 20, and sets the cutoff frequency of the digital filters 8 and 9. These filters are controlled so that f matches this parameter value f.

In the embodiment shown in FIG. 4, the luminance signal Y' is 0.5M
Hz and 1.5MHz low-pass filters 21 and 22, and the outputs of these filters 21 and 22 are
The signals are synthesized by the variable ratio synthesizer 23 at a ratio of (1-K) to K. Also, the luminance signal Y ^1/ 〓 is 0.5MHz and
The outputs of these filters 24 and 25 are (1-K).
A variable ratio synthesizer 26 synthesizes the signals at a ratio of K to K.
The outputs of the combiners 23 and 26 are added together in an adder 10 and used as a brightness signal for broadcasting. 2
7 is an arithmetic circuit that calculates the value K of K=I/(I+Q) from the color signal I component and Q component outputted by the matrix 2, and the output K is used to calculate the combination ratio of the additive ratio combiners 23 and 26. It's in control.

In the embodiment shown in Figure 4, the broadcasting brightness signal is, as shown in Figure 6, the low frequency part of 0.5 MHz or less is a signal Y' according to equation (1), and the high frequency part of 1.5 MHz or more is (4 ) is the signal Y ^1/ 〓 according to the equation. And from 0.5MHz
In the intermediate range between 1.5MHz, both signals Y' and Y ^1/ 〓 are mixed at a ratio of K to (1-K), and when the ratio of I component is large, the content of signal Y' is high. ,
Conversely, as the ratio of the I component decreases, the content of the signal Y ^1/ 〓 increases. Therefore, similar to the embodiments shown in FIGS. 1 and 3, it is possible to maximize resolution without impairing color reproducibility.

<Effects of the Invention> As described above, the present invention improves the reproducibility in the high range of luminance signals without impairing color reproducibility while achieving compatibility with the current broadcasting system. , it is possible to obtain high resolution images.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the video signal processing portion of a broadcasting device embodying the present invention, and FIG. 2 is a control characteristic diagram of the cutoff frequency of filters 8 and 9 in the same embodiment.
3 and 4 are block diagrams of other embodiments of the present invention, FIG. 5 is an explanatory diagram of the operation of the embodiment shown in FIGS. 2 and 3, and FIG. 6 is shown in FIG. 4. It is an explanatory diagram of operation of an example. 2 and 7... Matrix, 3-6... Gamma correction circuit, 8, 9, 21, 22, 24, 25... Filter, 10... Adder (synthesizing circuit), R, G, B
...Three primary color signals, Y...First luminance signal, Y ^1/ 〓...
...Second luminance signal, Y'...Third luminance signal, I,
I', Q, Q'...color signal.

Claims (1)

[Scope of Claims] 1. A first matrix that obtains a first luminance signal from three primary color signals; a gamma correction circuit that performs gamma correction on the first luminance signal to obtain a second luminance signal;
a gamma correction circuit that performs gamma correction on each of the three primary color signals; a second matrix that obtains a third luminance signal from the gamma-corrected three primary color signals; and a color obtained by the first or second matrix. A means for determining the ratio of the I signal component and Q signal component in the signal, and a third method in the band below 0.5 MHz.
It is a luminance signal of
In the band from 0.5MHz to 1.5MHz, if the above ratio is a value indicating that there are many I signal components, it is a value that indicates that the proportion occupied by the third luminance signal component is large and that there are many Q signal components. , the fourth luminance signal component accounts for a large proportion of the second luminance signal component.
a fourth luminance signal based on the ratio; and a fourth luminance signal and a color signal obtained by the second matrix to generate a broadcasting color television signal. Broadcasting equipment. 2 In the fourth luminance signal generation means, 0.5M
A boundary frequency that is continuously controlled according to the above ratio is set between Hz and 1.5MHz, the third luminance signal is extracted in the area below this boundary frequency, and the second brightness signal is extracted in the area above this boundary frequency. 2. A color television broadcasting apparatus according to claim 1, wherein the color television broadcasting apparatus extracts a luminance signal. 3 In the fourth luminance signal generation means, 0.5M
2. The color television broadcasting apparatus according to claim 1, wherein in a band between Hz and 1.5 MHz, the second and third luminance signals are mixed according to the above ratio.