JP2624686B2 - Image signal processing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal processing apparatus that performs predetermined signal processing on a plurality of input different color signals.

[Prior Art] FIG. 4 is a block diagram showing the configuration of a conventional example of a single-panel color camera using a solid-state imaging device.

In the figure, 1 is a solid-state imaging device, for example, a CCD,
R (red), G (green), and B (blue) primary color signals are output. 2,
Reference numerals 2a and 2b denote sample and hold circuits (S / H), which sample and hold three outputs from the solid-state imaging device 1, respectively. 3,3a and 3b are amplifiers. Reference numerals 4, 4a and 4b denote clamp circuits that fix (clamp) the black level to a predetermined potential. 5 is a gate circuit, 6, 6a, 6b and 6c are reduction filters (LPF), and 7, 7a, 7b and 7c are gamma correction circuits. 8 is a horizontal drive circuit, 9 is a vertical drive circuit, 10 is a timing generation circuit, 12 is an addition circuit, and 13 and 14 are subtraction circuits.

The R, G, B3 primary color signals output from the solid-state imaging device 1 and having the black level clamped by the clamp circuits 4, 4a and 4b are applied to the gate circuit 5 by applying a gate pulse from the timing generation circuit 10 to the gate circuit. 5 switches
SW-R, SW-G and SW-B are closed in order and gated sequentially to produce a luminance signal Y.

Further, the three color signals R, G, and B are band-limited by LPFs 6, 6a, and 6b to become R _L , G _L, and B _L , and are respectively γ-corrected by γ correction circuits 7, 7a, and 7b so as to match the characteristics of the CRT. to correct. Further gamma corrected color signal
R _L ^γ, B _L γ, are added by the adding circuit 12 from G _L ^gamma create a luminance signal Y _L ^gamma of the low-frequency, also subtractor luminance signal Y _L ^gamma from the color signals R _L ^gamma and B _L ^gamma by subtracting the 13 and 14, the color difference signals R _{L γ} -Y _{L ^γ,} and ^B γ -Y _L γ it is made.

The band of the luminance signal Y is limited by the LPF 6c,
is gamma corrected by the gamma correction circuit 7c outputs as the Y ^gamma.

[Problems to be solved by the invention]

In a three-tube color camera using an image pickup tube or a three-panel color camera using a solid-state image sensor, the luminance signal Y is Y = 0.3R ^γ + 0.59G ^γ +0 in order to match the spectral sensitivity of the human eye. 11B ^γ (1) The three primary color signals R, G, and B are added at a ratio as shown in equation (1).
In order to increase the resolution, the luminance signal Y is generated by sequentially gating the R, G, B signals by the gate circuit 5. Therefore, the luminance signal Y is equivalent to the addition of the three primary color signals of R, G, and B at a ratio of 1: 1: 1. That is, Y = 0.33R + 0.33G + 0.33B (2) When this signal is further γ-corrected, the following equation (3) is obtained.

^{Y γ = (0.33R + 0.33G +} 0.33B) γ ... (3) Further, the luminance signal component of the low band to produce a color difference signal Y _L ^gamma
Is a band-limited, γ-corrected color signal component R _L ^γ , G _L ^γ , B _L
It is made from ^γ by the addition method in the same manner as in equation (1).

Therefore, the color difference signals R _L ^γ -Y _L ^γ, and B _L ^γ -Y _L ^γ and the luminance signal Y ^gamma from the original primary color signals R, in making G, and B, and three-tube and three-plate type color camera of Since the luminance signal component (Equation (4)) and the luminance signal Y ^γ (Equation (1)) included in the color difference signal have the same value, faithful color reproducibility can be obtained. In the single-chip color camera, since the luminance signal component Y _L ^γ (Expression (4)) and the luminance signal Y ^γ (Expression (3)) included in the color difference signal have different values, correct color reproducibility cannot be obtained. Will be. In particular, a color having a low luminance signal level in equation (1), such as red or blue, and γ in equation (3)
Each coefficient has a value of about 0.6 due to the correction, so that the signal level becomes high. When displayed on a monitor, there is a disadvantage that the color becomes bright.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a luminance signal correction method that can solve the above-described drawbacks of the conventional example and can obtain correct color reproducibility in a single-chip color camera.

[Means for solving the problem]

In order to achieve such an object, the present invention provides an input unit for inputting a plurality of different color signals, a luminance signal generating unit for generating a luminance signal from the color signals, and a plurality of color difference signals from the color signals. Color difference signal generation means, a correction signal generation means for generating a correction signal by selecting a predetermined color difference signal according to the signal levels of the plurality of color difference signals generated by the color difference signal generation means, and And correcting means for correcting the ratio of a plurality of color components included in the luminance signal to improve color reproducibility.

[Operation] According to the present invention, a correction signal is generated by selecting a predetermined color difference signal according to the signal levels of the plurality of color difference signals, and the ratio of the plurality of color components included in the luminance signal is determined using the correction signal. Is corrected. Thereby, color reproducibility is improved. For example, the luminance signal is corrected to the ratio of the primary color signal that matches the spectral sensitivity of the human eye.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention.

In FIG. 1, the same parts as those in FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted.

11a is a NAM (Non Adder Mixe) newly added in this embodiment.
r) A circuit for detecting a peak level among the input color difference signals. 15 is a subtraction circuit.

Therefore, in the present embodiment, the luminance signal ^Yγ and the color difference signal
R _{L γ} -Y _{L ^γ,} and the ^B _L γ -Y _L γ produced in the same manner as described above prior art.

However, the color difference signals ^R _L γ -Y _L γ and ^B _L γ -Y _L γ
By inputting to the NAM circuit 11a, the color difference signal R ^γ -Y _L
^gamma, and from among B _L ^γ -Y _L ^γ, by peak detection to select those signal levels greater, by subtracting the subtraction circuit 15 from the luminance signal Y ^gamma and constant multiple is it,
The corrected luminance signal ^Yγ 'is output.

FIG. 2 is a waveform diagram when a color bar chart for explaining the operation of the embodiment shown in FIG. 1 is taken.

FIG. 2A shows a waveform of a luminance signal (formula (1)) when an image is captured by a three-tube color camera. FIG. 2B shows a luminance signal ((3)) when an image is captured by a single-chip color camera.
It is a waveform of (Formula).

Comparing the two, it can be seen that the level of the luminance signal indicated by the solid line in FIG.

Also, FIG. 2 (C) shows a waveform of the color difference signals R _L γ -Y _L ^γ, FIG. 2 (D) is a waveform of the color difference signal B _L γ -Y _L ^γ.

Write signal level large is selected by passing to the second view (C) and the color difference signals ^R _L γ -Y _L γ and ^B _L γ -Y _L γ the NAM circuit 11a of (D). For example, in FIG. 2, the color difference signal in the red portion of the color bar chart R _L ^gamma -Y
_L ^gamma is, the color difference signal B _{^L γ} -Y _{L γ} is selected in the portion of blue.
Then the chosen color difference signal multiplied by a constant is subtracted by the subtraction circuit 15 from the luminance signal Y ^gamma, RGB three contained in the luminance signal Y ^gamma
FIG. 2 (B) by changing the ratio of the primary color signal components.
Can be made the corrected waveform shown by the dotted line, and can be close to the waveform of FIG. 2 (A).

Accordingly, color reproducibility when displayed on a color monitor can be improved as compared with the above-described conventional example.

FIG. 3 is a block diagram showing the configuration of another embodiment of the present invention.

In FIG. 3, reference numeral 11b denotes a detection circuit, 301 and 302 denote slice circuits, and 303 denotes an addition circuit. The detection circuit 11b includes slice circuits 301 and 302 and an addition circuit 303.

Here, the NAM circuit 11a shown in FIG. 1 can be replaced with a detection circuit 11b shown in FIG. In other words, by passing the color difference signals ^R _L γ -Y _L γ and ^B _L γ -Y _L γ slice circuits 301 and 302, respectively, sliced at 0 level, taken out only positive signal, each of the color difference signals It is added in the addition circuit 303 subtracts the subtraction circuit 15 from a certain constant (alpha) multiplied to the luminance signal Y ^gamma. As a result, an effect similar to that of the above-described first embodiment can be obtained.

〔The invention's effect〕

As described above, according to the present invention, color reproducibility can be improved by correcting a luminance signal generated from a plurality of input different color signals.

[Brief description of the drawings]

 FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention, FIG. 2 is a waveform diagram illustrating the operation of the embodiment shown in FIG. 1, and FIG. 3 shows the configuration of another embodiment of the present invention. FIG. 4 is a block diagram showing a configuration of a conventional example. 1 ... fixed image sensor, 2, 2a, 2b ... sample hold circuit, 3, 3a, 3b ... amplifier, 4, 4a, 4b ... clamp circuit, 5 ... gate circuit, 6, 6a, 6b, 6c …… Low-pass filter (LPF), 7,7a, 7b, 7c …… γ correction circuit, 8,9 …… Drive circuit, 10 …… Timing generation circuit, 11a …… NAM circuit, 11b …… Detection circuit , 12,303 ... addition circuit, 13,14,15 ... subtraction circuit, 301,302 ... slice circuit.

Claims (3)

(57) [Claims] An input unit that inputs a plurality of different color signals; a luminance signal generation unit that generates a luminance signal from the color signals; a color difference signal generation unit that generates a plurality of color difference signals from the color signals; Correction signal generation means for generating a correction signal by selecting a predetermined color difference signal according to the signal levels of the plurality of color difference signals generated by the color difference signal generation means; and a correction signal included in the luminance signal using the correction signal. An image signal processing device comprising: a correction unit configured to correct a ratio of a plurality of color components to improve color reproducibility. 2. The image signal processing device according to claim 1, wherein said correction signal generating means generates said correction signal by selecting a maximum value of said plurality of color difference signals. Image signal processing device. 3. The image signal processing apparatus according to claim 1, wherein said correction signal generating means generates said correction signal by adding positive components of said plurality of color difference signals. Image signal processing device.