JPH0822073B2 - Color imaging device - Google Patents

Description

The present invention relates to a color image pickup device for obtaining a color image.

[Prior Art] A so-called single-plate color camera system for obtaining a color image using a single image sensor has been proposed more than ever before. In most cases, minute color filters are arranged in a mosaic pattern or a stripe pattern on the front surface of the image sensor, and the luminance signal and the color signal are obtained from the output of the image sensor.

FIG. 7 is a block diagram showing an example of a conventional color image pickup device. Reference numeral 1 is a lens, 2 is an image pickup device having a minute color filter arranged on the front surface, and 3 is a luminance signal (hereinafter Y signal) Y ₁ , red signal (hereinafter R signal) R ₁ , green signal (from the output of the image pickup device 2 A G signal) G ₁ and a blue signal (hereinafter B signal) B ₁ are separated by a color separation unit 4, a Y process unit including gamma correction, contour correction and clipping, and a circuit 5 similar to the Y process unit 4. A color processing unit having three sets, 6 is a matrix circuit for forming color difference signals by matrix calculation, 7 is a color encoder for forming a composite color television signal, and 8 is an output terminal.

In FIG. 7, a subject image is formed on the image pickup element 2 by the lens 1 and is taken out as an electric signal, and the color separation section 3 outputs Y signals Y ₁ , R, G and B signals R ₁ , G ₁ and B respectively. Separated into ₁ . The Y signal Y ₁ is subjected to processing such as gamma correction by the Y process unit 4 and becomes Y ₂ which is input to the color encoder 7. In addition, R ₁ , G ₁ , and B ₁ of the R, G, and B signals are the color processing unit 5
To R ₂ , G ₂ , and B ₂ after undergoing processing such as gamma correction, and subjected to matrix calculation in the matrix circuit 6 into color difference signals (RY) and (BY), and the color encoder unit 7
To form a composite color TV signal with Y ₂ .
It is output from the output terminal 8.

FIG. 8 shows an example of a minute color filter arranged on the front surface of the image pickup device 2 of FIG. 7, which has a striped red transmission filter section 10, a green transmission filter section 11, and a blue transmission filter section 12.
The three filter units are sequentially repeated.

In FIG. 7, the color separation unit 3 separates each color signal by sample-holding the Y signal by a low-pass filter that transmits a band below the color repetition frequency, and by separately holding each color signal corresponding to each color filter.

Further, FIG. 9 is a characteristic curve diagram showing characteristics by gamma correction in the Y process unit 4 and the color process unit 5, in which the vertical axis represents output and the horizontal axis represents input. As is clear from FIG. 9, for example, when a blue subject is imaged, if the blue color is a saturated color in the color processing unit 5,
Since the signal of 100% level is input, the output B _{2 of the} point C corresponding to the point A is obtained.

On the other hand, in the Y process unit 4, Y ₁ which is generally input
The B signal component in the signal is about 10% (however, it can be in the range of about 10 to 30% depending on the characteristics of the filter and the shooting condition). Therefore, if the characteristic curve of FIG. 9 is used, it corresponds to the point D. The gamma correction output Y _{2 at the} point F is obtained. This means that the gamma-corrected Y ₂ signal has a much higher value than the Y ₁ signal before gamma-correction.

Then, the B signal component in the Y signal increases, but
Since the gamma-corrected B ₂ signal in the color processing unit 5 is almost the same as the B ₁ signal before gamma-correction, a level difference between the Y signal and the color signal occurs in such a highly saturated blue object. As a result, the reproduced image of the subject becomes a bluish-white subject whose brightness is stronger than the blue of the actual subject.

Furthermore, B in the B ₂ signal and Y ₂ signal that have been gamma-corrected with each other
The gradation characteristics also differ depending on the component.

 Therefore, the output image becomes unnatural.

In this way, the difference between the levels of the luminance signal and the color signal and the gradation is similarly generated for other colors. Moreover, the magnitude of this gradation shift differs depending on the ratio of each color signal forming the luminance signal, and therefore differs depending on the color. In particular, it appears remarkably for blue.

Such a problem similarly occurs in a multi-plate or multi-tube color image pickup device.

[Problems to be Solved by the Invention] As described above, according to the conventional color image pickup apparatus, in a high-saturation subject, a difference occurs in the level and gradation of the luminance signal and each color signal during gamma correction, and the output image There was a problem that could not express the natural color of the subject.

The present invention has been made to solve the above-mentioned conventional problems, and provides a color image pickup apparatus capable of faithfully reproducing an image without a deviation of gamma correction characteristics or knee characteristics of a luminance signal and a color signal. The purpose is to

[Means for Achieving the Object of the Invention] In order to achieve the above object, the color image pickup apparatus of the present invention uses an image pickup means for converting an optical image into an electrical signal and a color signal obtained from the output of the image pickup means in a non-linear manner. Color signal non-linear correction means for correcting, brightness signal non-linear correction means for performing non-linear correction of the brightness signal obtained from the output of the imaging means, and B-from the color signal output from the color signal non-linear correction means
Color difference signal generating means for generating Y signal and RY signal, limit means for limiting negative signals of the BY signal and RY signal, respectively, and the BY output from the limiting means. Signal and RY signal are weighted and added respectively to obtain the output signal proportional to the luminance signal component in the BY signal and RY signal; and an output signal output from the adding means. Correction means for correcting the brightness signal to a ratio according to the above, and the correction means outputs the brightness signal output from the brightness signal non-linear correction means to the brightness signal in the BY signal and the RY signal. It is characterized in that it is corrected so as to match the component.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of the color image pickup apparatus of the present invention. In FIG. 1, reference numeral 20 denotes a correction signal generator for detecting the saturation (saturation) of a color signal, which receives two color difference signals RY and BY to generate a correction signal S ₁ .
It goes without saying that the color saturation detection method is not limited to this. The correction signal S ₁ serves to correct the characteristics of the Y process unit 4 in FIG. 7, and 200 is the Y process unit. 2 is a block diagram showing a specific example of the correction signal generator 20 shown in FIG. 1. Reference numerals 21 and 22 are limiter units for limiting signals below a zero level (achromatic color level is zero level). , 23 and 24 are attenuators for attenuating signals, 25 is an adder, and 26 is an inverting amplifier. In FIGS. 1 and 2, the same symbols as in FIG. 7 indicate the same or corresponding parts.

In FIG. 1, the color difference signals RY and BY input from the matrix circuit 6 are limited below the zero level by the limiters 21 and 22, respectively, and the outputs of the limiters 21 and 22 are attenuated by the attenuators 23 and 24, respectively. And adder 25
Are added to each other, inverted and amplified by the inverting amplifier 26 and output.

The operation of the correction signal generator 20 will be described with reference to FIG. Here, one unit of the three primary color signals (R, G, B) is 1 (V)
A case where the achromatic color level is set as a reference (0 (V)) will be described.

First, when the color difference signals R-Y and B-Y are both 0 (V), the correction signal S ₁ output from the inverting amplifier 26 is the normal gamma characteristic (without correction) shown in FIG. S ₁ = 1 (V) is output so that

The inverting amplifier 26 is provided with an offset so that S ₁ = 1 is output in the above case. In addition, the correction signal S ₁ =
1 is a reference voltage 35 and gamma setting resistors 36, 37, 38 in FIG.
It is set based on.

When the color difference signals R-Y and B-Y are both 0 (V) or less, the output of the limiters 21 and 22 is 0, so that the correction signal S ₁ is 0 (both of the color difference signals R-Y and B-Y). S ₁ = 1 as in V)
Is output. This is shown in the lower left quadrant of FIG. 3 (area where the color difference signals RY and BY are both negative).

Next, the color difference signal RY is at the maximum level (in this embodiment,
It is assumed that it becomes 1 (V) due to the filter characteristics, etc.), and when BY is 0 (V), the output of the limiter 21 is the same as the input signal and the output of the limiter 22 is 0. Therefore, a value attenuated by the attenuator 23 is input to the output of the limiter 21 via the adder 25 and is inverted by the inverting amplifier 26, so that the output decreases. At this time, if the attenuation ratio of the attenuator 23 is 0.6, the correction signal S1 output by the inverting amplifier 26 will be 0.4 (V).

On the other hand, assuming that the attenuation ratio of the attenuator 24 is 0.8, when the color difference signal RY is 0 (V) and the color difference signal BY is at the maximum level (in this embodiment, it is 1 (V) due to the filter characteristics and the like. Assuming the case), the correction signal S ₁ becomes 0.2 (V).

The values thus obtained are shown by the contour lines in FIG.

FIG. 4 is a block diagram showing a specific example of the Y process unit 200 in FIG. 1, 31 is a clamp circuit, 32 is a gamma correction circuit as a non-linear circuit, 33 is a clipping circuit for performing white clipping and dark clipping, 34 is a contour correction circuit,
Reference numeral 35 is a reference voltage, and 36, 37 and 38 are gamma setting resistors.

Y signal Y ₁ input to the clamp circuit 31 in FIG.
Is clamped to the reference voltage 35 by the clamp circuit 31, and gamma corrected by the gamma correction circuit 32. The characteristics of this gamma correction can be changed by a set voltage supplied from the outside. When the correction signal S ₁ is 1, the resistors 36, 37 and 38 are selected so that an appropriate gamma characteristic can be obtained. There is.
The gamma-corrected output is clipped by the clipping circuit 33 to the signals of the white and dark parts, and the contour correction circuit 34
After the contour correction is performed in (1), it is output as a Y signal Y ₂ . Fourth
In the circuit shown in the figure, when the correction signal S ₁ decreases, the set voltage for gamma correction in the gamma correction circuit 32 decreases, and the gamma correction characteristics change.

FIG. 5 is a diagram showing an example of changes in gamma correction characteristics, in which the horizontal axis represents input and the vertical axis represents output.

When the correction signal S _{1 is} 1, the gamma correction characteristic is normal as shown in FIG. 5 (1) by the reference voltage 35 and the gamma setting resistors 36, 37 and 38 in FIG. The color for outputting the correction signal S ₁ = 1 is as shown in FIG.
Both B and Y are signals of negative polarity, and have a strong green color. In this area, the gradation shift is rare and is not a problem, so correction is not performed.

Further, when the correction signal S ₁ = 0.4, the reference voltage 35 in FIG.
And the gamma setting resistors 36, 37 and 38 change the gamma correction characteristics as shown in FIG.
The output changes to pass the 40% -40% point. As a characteristic color difference signal for which the correction signal S ₁ = 0.4, RY is 1,
This is the time when BY is 0, and this point shows a substantially red color with high saturation. Therefore, the correction of FIG. 5 (2) is performed in which the luminance signal is input to about 40% of the color signal (varies depending on the shooting condition and the characteristics of the filter).

When the correction signal S ₁ = 0.2, the reference voltage 35 in FIG. 4 is changed, and the gamma setting resistors 36, 37, 38 change the gamma correction characteristics as shown in FIG. 5 (3). Input-output 20
It changes so as to pass the point of% -20%. This correction signal S ₁ =
As a characteristic color difference signal of 0.2, RY is 0, BY
Is 1 and this point indicates a substantially blue color with high saturation. Therefore, the luminance signal is input to about 20% of the color signal (varies depending on the shooting condition and the characteristics of the filter), and the correction of FIG. 5B is performed.

As described above, the correction signal S ₁ shown in FIG. 3 is set based on the ratio of each color signal forming the luminance signal. Further, the attenuation ratios 0.6 and 0.8 of the attenuators 23 and 24 used to obtain the correction signal S ₁ are also set based on the ratio of each color signal in the luminance signal.

FIG. 6 is a block diagram showing another specific example of the Y process unit 200 in FIG. 1. Reference numeral 40 is a compression circuit called a knee circuit as a non-linear circuit, and 41 and 42 are knee setting resistors. The knee circuit 40 performs an operation of compressing a signal having a level equal to or higher than a set value at a predetermined ratio (about 1/5 to 1/20), and a reference voltage 3
5, the set value is determined by the correction signal S ₁ and the resistors 41, 42.

Y signal Y ₁ input to the clamp circuit 31 in FIG.
Is clamped to the reference voltage 35 by the clamp circuit 31,
Further, the knee circuit 40 compresses a signal having a level equal to or higher than the set value at a predetermined ratio, and the gamma correction circuit 32 performs gamma correction. Then, the gamma-corrected output is output as the Y signal Y ₂ after the white and dark part signals are clipped by the clipping circuit 33 and the contour is corrected.
In the circuit of FIG. 6, when the correction signal S ₁ decreases,
The set voltage is reduced in the knee circuit 40, and the compression characteristic of the knee circuit 40 changes.

In each of the above-described embodiments, the correction signal is obtained from the color difference signal which is the output of the matrix circuit, but the color signals (R, G,
B) or color signals and luminance signals (R, B, Y, etc.). Further, various characteristics can be considered other than those shown in FIG. 3, and the characteristics can be set by a look-up table by digital technology.

In the above embodiment, the non-linear correction characteristic of the luminance signal side is controlled so as to match the color signal side, but conversely, the non-linear correction characteristic of the color signal is controlled so as to match that of the luminance signal side. The invention includes.

[Effects of the Invention] As described above, according to the present invention, the BY signal and the RY signal are generated from the non-linearly corrected color signal, and the BY signal and the RY signal are generated. The non-linearly corrected luminance signal is corrected to a different ratio, and the luminance signal and the color difference signal on the output side are corrected to have a predetermined ratio.
It is possible to faithfully reproduce the picked-up image without causing the characteristic deviation of the non-linear correction of the luminance signal and the color signal when picking up the subject of any color.

Also, for a specific hue range (range of strong green color) that does not require correction, the negative signals of the BY signal and the RY signal are each limited to a signal that is not corrected, and this limit Since the corrected signals are formed by weighted addition of the generated signals, the specific hues that do not need to be corrected are excluded from the correction target by a simple process of limiting the BY signal and the RY signal. For hues that need correction, for example, a troublesome process of previously providing a correction table according to the hues is not required, and
The optimum correction signal can be obtained by a simple calculation process of weighted addition of the signal and the RY signal.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the image pickup apparatus of the present invention, FIG. 2 is a block diagram showing a specific example of the correction signal generator of FIG. 1, and FIG. 3 is a correction signal generation of FIG. FIG. 4 is a block diagram showing one specific example of the Y process in FIG. 1, FIG. 5 is a diagram showing an example of changes in gamma correction characteristics, and FIG. FIG. 1 is a block diagram showing another specific example of the Y process unit in FIG. 1, FIG. 7 is a block diagram showing an example of a conventional image pickup apparatus, and FIG. 8 is a minute color arranged on the front surface of the image pickup element in FIG. FIG. 9 is a diagram showing an example of a filter, and FIG. 9 is a characteristic curve diagram showing the characteristic by gamma correction in the Y process section and the color process section. In the figure: 1: Lens, 2: Image sensor 3: Color separation part, 5: Color process part 6: Matrix circuit 7: Color encoder 20: Correction signal generator 200: Y process part

Claims (1)

[Claims] 1. An image pickup means for converting an optical image into an electrical signal, a color signal nonlinear correction means for nonlinearly correcting a color signal obtained from the output of the image pickup means, and a luminance obtained from the output of the image pickup means. A luminance signal non-linear correction means for non-linearly correcting the signal, and B from the color signals output from the color signal non-linear correction means
-Color difference signal generating means for generating Y signal and RY signal, limit means for limiting negative signals of the BY signal and RY signal, respectively, and the B-output from the limiting means Y signal, RY
The signals are respectively weighted and added, and the BY signal and RY signal are added.
An addition unit that obtains the output signal proportional to the luminance signal component in the signal, and a correction unit that corrects the luminance signal to a ratio according to the output signal output from the addition unit, the correction unit, A color image pickup apparatus, wherein the luminance signal output from the luminance signal non-linear correction means is corrected so as to match the luminance signal components in the BY signal and the RY signal.