KR920000984B1 - Color television transmitting method - Google Patents

Abstract

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Description

Color TV transmission method for transmitting luminance signal and low-pass filtered color signal

1 is a block diagram showing the principle of a color television transmission system.

2 is a diagram showing human visual characteristics.

3 is a diagram showing an equivalent luminance signal in one scan line of a standard color bar pattern.

4 is a diagram showing the characteristics of a compensation signal for a color bar pattern.

5 is a diagram showing an FBAS signal compensated by ΔEy.

6 is a block diagram showing a compensation signal generating circuit according to the present invention.

* Explanation of symbols for the main parts of the drawings

A: Camera C: Coder Matrix

D: decoder matrix W: color receiver

F ₁ : Camera Filter Ph: Phosphor of Water Tube

KE: Compensation Signal Generation Circuit LP: Low Pass Filter

SU: Addition

The present invention relates to a color television transmission method for transmitting a luminance signal and a low-pass filtered color signal.

In the standardized color television transmission system, gamma pre-correction is performed when the color value is changed to the primary color signal on the imaging side. This gamma precorrection “precorrects” the nonlinearity that results from a typical cathode ray tube, thereby causing gamma distortion. The principle of the color television transmission system as described above is shown in FIG.

The color values of the pixels to be photographed are indicated by standard color values X ₁ , Y ₁ , and Z ₁ . The photographing camera A linearly converts the photographed beam into the primary color signals E _RO1 , E _GO1 , E _BO1 . These signals are gamma precorrected according to the following equation.

In the above formula,

The gamma pre-corrected primary color signal is linearly converted into luminance signals E _Y1 , and color signals E _U1 , E _V1 by the coder matrix C. FIG.

The signal is processed for transmission, transmitted, inversely transformed and appears on the receiving side as signals E _y2 , E _U2 , E _V2 . From these signals, primary color signals E _R2 , E _G2 and E _B2 for controlling the color picture tube by the decoder matrix are obtained. In a standardized color television transmission system, the color filter F ₁ of the camera is matched to the reproduction phosphor Ph. In addition, the coder matrix and the decoder matrix, and the camera and the water tube interact with each other. If the luminance signal and the color signal do not change during the processing, transmission and inverse conversion of the signal, the reproduction standard color values X ₂ , Y ₂ and Z ₂ will match the original standard color values X ₁ , Y ₁ , Z ₁ . However, if the luminance signal or the color signal changes, the two values will not coincide.

If the color signal changes, regeneration failure occurs. This corresponds to the known fact that the luminance decreases when the color image is reproduced in black and white. This reduction in luminance is significant in the case of high saturation and in the case of colors (e.g. blue) that are originally low in luminance.

The problems of the prior art will be described in more detail with reference to FIGS. 2 and 3 as follows.

In a standardized color television transmission system, the primary, red, green, and blue primary signals E _R1 , E _G1 and E _B1 are converted into luminance signals E _Y1 and two color signals E _U1 and E _V1 . This conversion is performed for the purpose of dividing the entire signal of the beam optical image into a component mainly focusing on luminance and a component mainly focusing on color, except that it is compatible with existing black and white television transmission systems. The division of the beam optical image into luminance and color is to take advantage of human visual characteristics. 2 shows human visual characteristics with respect to contrast sensitivity for a color modulation grid and a luminance modulation grid. According to this figure, the resolution of chromaticity difference of human vision is only 10-20% of that of luminance difference. Therefore, chromaticity can be reproduced with a narrow bandwidth compared to the luminance. This is why standardized bandwidth reduction is performed on color signals. However, since the signal is processed at the level of the gamma pre-corrected signal, the bandwidth reduction of the color signal affects the reproduction luminance. The reproduction luminance is proportional to the color value Y ₂ . Therefore, Y is also called relative brightness. Thus, Y ₂ is according to the following formula is obtained from saekchi _{R 2, G 2, B 2} .

In the above formula, Y ₂ , R ₂ , G ₂ , B ₂ ∈ [0; 1]

The coefficients b _R , b _G , b _B depend on the standardized reproduction color values. in this case,

The following formula holds in two standards.

Corresponding to formula (3), the luminance signal is formed from the primary color signal. for example,

Wherein E _R2 , E _G2 , E _B2 ∈ [0; 1]

In the FCC standard, the coefficient for the primary color signal and the coefficient of the color value are set equally. In other words,

In the EBU standard, the primary color signal coefficients are quoted from the FCC standard. Equation (6) is only approximate in the EBU standard. Since the effect of color signal fluctuation can be detected well by this property, it is assumed that the above formula holds. Hereinafter, a so-called color difference signal is used as the color signal.

In equation (7), both are linearly independent. Moreover, the following formula holds.

In Equations (7) and (8), the size of the prime is proportional to the corresponding size of no prime in FIG. The size of the frying is different from the size of the non-priming coefficient for the color difference signal. Considering the equations (5), (6), (7), (8) and the nonlinear relationship between the color value and the color value control signal, the equation (3) in FIG. 1 is modified as follows.

The nonlinearity of the current color television receiver is represented by a gamma value of 2.2 to 2.8. If the value of γ is 2.5, which is the average value for most of the CRTs, the nonlinearity is approximated sufficiently accurately. This value is the basis for later quantitative evaluation.

, 즉 흑백화상을 전송하는 경우, 또는 γ=1인 경우에만 휘도가 E_Y2에 의하여 결정되어진다. 이 식에서, γ=1일때 칼라화상의 휘도는 흑백화상의 휘도보다 작아진다는 것을 알 수 있다. 오늘날의 표준 텔레비젼 전송계에서는, γ값이 1보다 큰 것을 기초로 하고 있다. 따라서 최종 색신호값에 의해 재생휘도가 높아진다. 이러한 사실은 재생휘도의 일부분이 색채널을 통해서 전송된다는 것을 의미한다.As can be seen from equation (9),

That is, the luminance is determined by E _Y2 only when the monochrome image is transmitted or when γ = 1. In this equation, it can be seen that when γ = 1, the luminance of the color image is smaller than the luminance of the monochrome image. In today's standard television transmission systems, γ is based on a value greater than one. Therefore, the reproduction luminance is increased by the final color signal value. This fact means that part of the reproduction luminance is transmitted through the color channel.

In the case of low pass, the color value control signal is represented by the following equation.

The index L is attached to the low-pass filter in Equation (10). On the other hand, the index H is attached to the difference between the original signal and the low pass filtered signal. As can be seen from the right side of Equation (10), proper control of the regeneration circuit is performed only for the low pass component. “High band component” is denoted by E _Y2H in the final chromaticity. This can cause significant luminance disturbances when chroma is high.

FIG. 3A and FIG. 3B show an equivalent luminance signal in one scan line with respect to the standard color bar pattern with and without color signal low pass filtering. This equivalent luminance signal has a relationship represented by the relative reproduction luminance and the following equation.

As can be seen from FIGS. 3A and 3B, low-pass filtering of color signals in a standard transmission system impairs reproduction luminance. The reason for this is that, as described above, the color signal contains a certain amount of luminance components, and the corresponding luminance components are also low-filtered due to the low-pass of the color signal.

It is an object of the present invention to reduce or eliminate such luminance disturbances.

The object is to generate a compensation signal from an input signal or an output signal of a coder matrix and a low-pass color signal by means of a compensation signal generating circuit before transmitting to a band limited channel in accordance with the invention, wherein the compensation signal is added from the coder matrix at the adder stage. And a luminance signal to be transmitted by adding to the luminance signal of the color television.

According to the present invention, compensation of luminance disturbance is performed only for the "high frequency component". That is, the luminance disturbance can be compensated by the signal high-band component that can be transmitted only in the luminance signal channel when compatibility is required. The corresponding compensation value [Delta] Ey is superimposed on three control signals of equation (10). The compensation signal _ΔEy is obtained according to the following equation by setting the actual luminance and the set relative luminance Y _so11 to be the same.

Equation (12) can be evaluated in various forms. When the initial value is properly estimated, an approximation is obtained by the expansion of the water supply by the linear element. 4A shows the basic characteristics of the compensation signal for the color bar pattern described above. 4B shows an NTSC or PAL composite image signal compensated by [Delta] Ey. As can be seen from FIG. 2, the total signal exceeds the limit of the entire signal only in the black signal region compared with the case where the compensation is not performed. By limiting the height of the standard signal, the compensated signal is compatible with existing standard televisions.

5 illustrates an embodiment of a circuit for generating and using a compensation signal to compensate for luminance disturbances according to the present invention. This circuit is provided with a compensation signal generation circuit KE in addition to the circuit shown in FIG. The compensation signal generating circuit generates and supplies the compensation signal? Ey digitally (e.g. in the form of a computer) or analogue to the addition stage SU according to equation (12). The compensation signal is obtained only when the "setting state" is detected. The "setting state" can be detected only on the imaging side.

The luminance disturbance caused by the low pass of the color signal is compensated for by the compensation signal transmitted through the luminance channel of the conventional image transmission system. This produces an effect similar to the case of linearizing the image capturing / transmitting / reproducing system by performing gamma precorrection right in front of the receiving tube. The precompensation method described above can be configured to be compatible with current standardized signal processing transmission technology.

In FIG. 5, signals E _U1 ′, E _V1 ′ are supplied to the compensation signal generation circuit KE from the output of the coder matrix or selective signals E _R1 , E _G1 , E _B1 are supplied from the input side of the coder matrix.

Compensation signal ΔEy

a) repeatedly obtained, for example, from equation (12)

b) obtained from an approximate solution to γ-2.

Forecast

Linear approximation obtained by ΔE _Y1

Better approximation

or

The present invention can improve the reproduction luminance without changing the water phase.

Claims (2)

In a color television transmission method for transmitting a luminance signal low-pass filtered color signal, input signals E _R1 , E _G1 , E _B1 of the coder matrix C by the compensation signal generation circuit KE before transmission on a band limited channel. Or a compensation signal _ΔEy is generated from the output signals E _Y1 , E _U1 ′, E _V1 ′ and the color signals E _U1L ′, E _V1L ′, which are low-pass filtered by the low pass filter LP, and the compensation signal. (△ E _Y) for the luminance signal and the low-band, characterized in that comprising the step of forming an addition stage (SU) corner of the matrix (C) the luminance signals (E _Y1) a luminance signal (Y _SO11) to be transmitted by adding in from at Color TV transmission method for transmitting the filtered color signal. The color television transmission method according to claim 1, wherein the luminance signal Y _{SO11 to} be transmitted satisfies the following equation:

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