JPS6158076B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a gamma correction method for a color imaging device that obtains a color television signal using a separate luminance method, and more particularly to a gamma correction method for a color device using a separate luminance method that includes a white signal, a cyan signal, and a yellow signal. A color imaging device that separates incident light into white component light, cyan component light, and yellow component light has already been proposed by the same applicant as the present invention (Japanese Patent Application No.
112770), it can be said to be an effective color imaging device when improved sensitivity is required. The present invention proposes an effective gamma correction method for this type of color imaging device. Regarding the gamma correction method for this type of separated luminance type color imaging device, two methods are proposed in the aforementioned Japanese Patent Application No. 112,770/1983. One method is to pass the white, cyan, and yellow signals as they are through a process amplifier and pass them through a generally known gamma correction circuit, which is the same as the conventional three primary color signals of red, green, and blue. This method uses a video amplification circuit in the path. Another method is to combine the luminance signal and two types of color difference signals in a matrix circuit, without passing the white, cyan, and yellow signals through a generally known gamma correction circuit. Through a commonly known gamma correction circuit, the two color difference signals modulate the subcarrier signal into a chrominance signal, which increases the gain of the chrominance signal when the luminance signal is at a low level. , the circuit is configured to reduce the gain of the chrominance signal when the luminance signal is at a high level, and the red signal, green signal,
This method attempts to achieve an effect similar to the normal gamma correction method in which each green signal passes through a gamma correction circuit. In the former method, the signal passing through the gamma correction circuit is a red signal, a green signal, and a signal corresponding to the receiver's three primary color signals.
Instead of a green signal, a white signal is the sum of these three signals, a yellow signal is the sum of a red signal and a green signal,
Since the cyan signal, which is the sum of the green signal and the blue signal, passes through the gamma correction circuit, an error occurs from the normal gamma correction amount. In the latter method, the control signal for gamma correction is generated from the luminance signal, and since the luminance signal is a mixture of red, green, and blue signals at a ratio of 0.3, 0.59, and 0.11, respectively, accurate gamma correction is possible. It is not. This is because when the intensity of blue light is at the reference level, the blue signal is 1, the red and green signals are 0, and the luminance signal is 0.11, so originally it is necessary to change the levels of both the luminance signal and chrominance signal. Since the luminance signal level is small even though there is no error, the gain of the chrominance signal is increased and the luminance signal is also gamma corrected, so it is clear that an error has occurred in the gamma correction. In this latter method, the ratio for combining luminance signals for green and red signals is 0.11 or 0.3, which is a small value compared to green signals, so the red and red signals are corrected more than necessary compared to green signals. It has become clear that the condition for color reproduction, where the gamma correction characteristics of the three primary color signals of green and blue are the same, so-called gamma balance, has been disrupted, resulting in a deterioration in image quality. The present invention relates to an improvement of the above-mentioned Japanese Patent Application No. 53-112770,
The aim is to provide an improved gamma correction scheme with fewer errors. The present invention is a color imaging device (hereinafter referred to as W) that separates incident light into white component light, cyan component light, and yellow component light.
-YeCy color imaging device),
The matrix circuit is provided with a circuit for obtaining gain control signals corresponding to each of the two types of color difference signals, and the two types of control signals obtained by this circuit are
Gamma correction with less error is performed by adding it to gain control circuits corresponding to each of the two types of color difference signals provided in a signal path that synthesizes a chrominance signal having a subcarrier signal from the two types of color difference signals. can be achieved. That is,
In Japanese patent application No. 112770, the amplitude (gain) of the chrominance signal is controlled by a control signal formed from the luminance signal, so only limited color signals in the red, green, and blue signals can be gamma corrected. Even when corresponding gain control must be performed, since the luminance signal includes all red, green, and blue signals, gain control is performed in the same way even for color signals that do not require gain control, and gamma This would result in over-correction. In order to eliminate such drawbacks, the present invention calculates the control signal to be applied to the gain control circuit in the signal path corresponding to the two types of color difference signals from the ratio of the red signal, green signal, and blue signal to each color difference signal. The purpose of this is to reduce errors by creating a signal that is synthesized. A detailed explanation will be given below using specific examples with reference to the drawings. FIG. 1 is a block diagram showing a first embodiment of the present invention, in which three signals from input terminals 1, 2, and 3, that is, a white signal (W), a yellow signal (Ye), and a cyan signal (Cy) are connected to a matrix circuit 4. , the luminance signal Y,
The two types of color difference signals R-Y and B-Y are combined and sent to a gamma correction circuit 5 and modulators 6 and 7 that amplitude modulate the subcarrier, respectively. The output of modulator 6 is sent to gain controller 10, and the output of modulator 7 is sent to gain controller 1.
Sent to 1. On the other hand, the matrix circuit 4 has a red signal R and a green signal G.
The blue signal B is synthesized and the color difference signal R is obtained from these three signals.
-Y control signal synthesis circuit 8 that synthesizes a signal that controls the gain of the color difference signal B-Y, and a B-Y control signal synthesis circuit 9 that synthesizes a signal that controls the gain of the color difference signal B-Y. Output signal to gain controller 1
The gain controller 10 controls the gain of the color difference signal R-Y having a carrier wave at 0 and 11 to an amplitude corresponding to gamma correction, and converts the color difference signal B-Y having a carrier wave to
A gain controller 11 controls the gain to an amplitude corresponding to gamma correction. The signals controlled by the gain controllers 10 and 11 are sent to a mixer 12 to become a chrominance signal, mixed with a luminance signal Y in a mixer 13, and sent to an output terminal 14 as a color television signal. Here, we will give one specific example of the concept of the R-Y control signal synthesis circuit 8 and the B-Y control signal synthesis circuit 9. Considering the R-Y control signal, as shown in FIG. The direction of the vector of red signal R, green signal G, and green signal B shown on the Y axis and B-Y axis is B
θ _R (=103°) and θ _G (=
241°) and θ _B (=347°). Considering the degree of contribution of these three color signals to the RY axis, the RY control signal can be expressed by the following equation. _RY (aR | sinθ _R | +bG | sinθ _G | +cB | sinθ _B |) -(1) Here, a, b, and c are constants, and R, G, and B are the signal levels of the red signal, green signal, and blue signal, respectively. represents. In gamma correction, the gain is higher for low-level signals and lower for high-level signals, so when R, G, and B in equation (1) are small values, the gain is increased by |sinθ _R |, |sinθ _G | and |sinθ _B | must be controlled to increase the gain when they have large values. That is, R, G, B and |sinθ _R |, |
It works in the completely opposite direction to sinθ _G | and |sinθ _B |, and if the constants a, b, and c have arbitrary values, equation (1) cannot obtain accurate gamma correction. For example, by selecting the constants a, b, and c as values expressed by the following equations, there is no contradiction and gamma correction becomes possible.

[Table] Therefore, equation (1) becomes _RY (R+G+B−R|sinθ _R | −G|sinθ _G |−B|sinθ _B |) −(3). Similarly, the BY control signal can also be expressed by the following equation. _BY (R+G+B−R | cosθ _R | −G | cosθ _G | −B | cosθ _B |) - (4) Both equations (3) and (4) indicate that the gain controller 10 and 11, and when the variable in this range has a large value, the gain controller 1
If the gain of 0 and 11 is made to work in the direction of decreasing, it is possible to obtain the correct amount of gamma correction. In equations (3) and (4), θ _R = 103°, θ _G = 241°, θ
By substituting _B 347°, it can be expressed as the following equation. _RY (0.026R+0.125G+0.775B) -(5) _BY (0.758R+0.515G+0.026B) -(6) FIG. 3 is a modification of FIG. 1 and shows a block diagram showing another embodiment. Circuits with the same functions as in FIG. 1 are indicated by the same symbols. That is, the difference from FIG. 1 is that the order of signal flow between the modulator and the gain controller is reversed. In FIG. 1, the gain of the signal modulated by the modulator 6 or 7 is controlled, but in FIG. 3, the gain of the color difference signal itself is controlled by the gain controller 10' or 11', and then Although the configuration is such that the modulation is carried out at 1' or 7', the effect itself is no different from the case shown in FIG. As described above, the present invention approximates gamma correction by deriving the proportion contributing to two types of color difference signals from the respective vectors of the red signal, green signal, and blue signal by the amounts projected onto the respective color difference axes. The degree of this will also be further improved. As explained above, the W-YeCy method improves sensitivity but has problems with color reproduction, but by adopting the gamma correction method of the present invention, the correction error can be reduced and color reproduction is improved. It can be improved on. If red, green, and blue signals are to be synthesized from white, yellow, and cyan signals in order to synthesize the control signals shown in the present invention, it is better to convert these signals into color television signals. Although it may seem obvious at first glance, the red, green, and blue signals formed in this way are obtained by synthesizing the difference signals from the input white, yellow, and cyan signals, so the signal-to-noise ratio is low. It's getting worse. Therefore, in the present invention, even if the band is narrow and the signal-to-noise ratio is somewhat poor, such as the control signal for gamma correction, if it is used in a place where the degree of deterioration of the overall image quality is small, it will not cause much deterioration of image quality. . Therefore, when the gamma correction of the present invention is employed, it is possible to obtain the advantage that not only the sensitivity is improved but also there is little deterioration in image quality in terms of color reproduction. Note that the present invention is not limited to the embodiments, and for example, the R-Y control signal synthesis circuit 8 and the B-Y control signal synthesis circuit 9 do not synthesize the red signal R, the green signal G, and the blue signal B. The same effect can be obtained by incorporating the circuit into the matrix circuit 4 and directly synthesizing the respective control signals from the white signal W, yellow signal Ye, and cyan signal Cy, and this is not within the scope of the present invention. it is obvious. Further, the control signal is not limited to those expressed by equations (5) and (6), but any control signal that is based on a concept that satisfies equation (1) is included within the scope of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the invention, FIG. 2 is a vector diagram of red, green, and green lights, and FIG. 3 is a block diagram showing another embodiment of the invention. In addition, in the figure, 1 is the input terminal of the white signal W,
2 is an input terminal for the yellow signal Ye, 3 is an input terminal for the cyan signal Cy, 4 is a matrix circuit, 5 is a gamma correction circuit, 6 and 6' are R-Y signal modulators,
7, 7' are B-Y signal modulators, 8 is an R-Y control signal synthesis circuit, 9 is a B-Y control signal synthesis circuit, 1
0 and 10' are gain controllers for the R-Y signal system; 11;
11' is a gain controller for the B-Y signal system, 12, 13
represents a mixer, and 14 represents an output terminal.

Claims (1)

[Claims] 1. A separation optical system that separates incident light into cyan component light, yellow component light, and white component light that has spectral characteristics that encompass the spectral characteristics of these two component lights, and an imaging device that converts these three component lights into electrical signals. In a gamma correction method for a color imaging device, which includes a device and a matrix circuit that synthesizes a luminance signal and two types of color difference signals from a cyan signal and a white signal converted into electric signals, A circuit is provided to obtain a gain control signal corresponding to each of the types of color difference signals, and the two types of control signals obtained by this circuit are combined into a chrominance signal having a subcarrier signal from the two types of color difference signals. A gamma correction method for a color imaging device, characterized in that the gamma correction method is applied to a gain control circuit corresponding to each of the two types of color difference signals provided in the path.