JPH0422076B2 - - Google Patents

Description

[Detailed description of the invention] (Technical field) The present invention relates to improvements in color imaging devices.

(Prior Art) Conventionally, for example, as shown in FIG. 1, R (red),
It is known that a stripe filter consisting of a repeating arrangement of Cy (cyan) and G (green) is provided in front of the light receiving section of a solid-state image sensor, and each color filter is arranged in a one-to-one correspondence to the pixel pitch of the image sensor. There is.

If the horizontal readout clock frequency of an image sensor using such a filter is _R , the carriers of each color signal exist at the same 1/3 _R position with a phase shift of 2/3π as shown in Figure 2. .

Especially when photographing a subject with zero color saturation,
If the overall spectral characteristics of the system consisting of the image sensor, color filters, etc. are set so that the image sensor output is obtained equally for each color component, the sideband signals of each color existing in 1/3 _R shown in Figure 2 can be The vectors cancel each other out, and so-called "aliasing distortion", which is the mixing of sideband components into the baseband component used as the luminance signal, is eliminated.

Originally, this kind of balance effect can only be obtained for achromatic subjects, but since most of the subjects that are normally imaged have low color saturation, in practice it is necessary to use a frequency band above the Nyquist frequency of each color signal. Performs signal processing.

However, if a subject with high color saturation enters the screen, the sampling frequency will drop to 1/3 _R , and the Nyquist frequency will also drop to 1/3.
It drops to 6 _R. Therefore, for a subject image having a spatial frequency component of 1/6 _R or more, aliasing distortion occurs and the image quality deteriorates significantly.

On the other hand, it is known that such a high resolution is not necessary for visually photographed subjects with high color saturation.

(Purpose) The present invention has been made in view of this background.
It is an object of the present invention to provide an improved imaging device that does not generate moiré or the like even for subjects with high color saturation.

(Embodiment) For this purpose, in an embodiment of the present invention, the level difference or ratio between the red signal formed from the electrical signal output from the imaging means and the brightness or a signal corresponding to the brightness is calculated, and the brightness is calculated based on the calculation output. The configuration is such that the frequency characteristics of the signal contour compensation means are controlled.

The present invention will be explained in detail below based on the embodiment shown in the third diagram.

1 in the figure is a solid-state image sensor, such as CCD or MOS
An XY address system or the like can be applied, and of course an image pickup tube may also be used. 2 is a solid-state image sensor 1
This is a low pass filter for removing clock components from the output signal of the

Reference numeral 4 denotes a γ correction circuit for applying γ correction to the pseudo Y signal. Reference numeral 5 denotes a contour compensation circuit as contour compensation means according to the present invention, which controls the high frequency component of the luminance signal.

6, 7, and 8 are sample and hold circuits for separating R, G, and Cy color signals, respectively; 12 is a (Cy
- a subtractor for obtaining a B (blue) signal by subtracting G); 9 to 11 are white balance circuits for white balancing each of the R, G, and B color signals; 13 to 11; Reference numeral 15 denotes a γ correction circuit which applies γ correction to each color signal.

16 and 17 are subtracters, R-G and B, respectively.
- form a G signal. 18 and 19 are low pass
It is a filter, and the color difference signal band is
This is to limit the frequency to 500KHz or less. 20 is an encoder for forming an NTSC signal from a luminance signal, color difference signal, synchronization signal, etc. 22 is R,
This is an adder for the G signal, and this output signal (G+B)
is input to the DC amplifier 23, and the difference with the R signal is amplified. FIG. 4 is a diagram showing an example of its configuration. The differential signal V _C1 of the DC amplifier 23 is sliced at an appropriate potential in the slicing circuit 24,
This becomes the V _C2 signal shown in Figure b. This V _C2 signal has its signal amplitude and potential changed by a control signal generator 25 in the next stage, and becomes a control signal V _C3 for controlling the contour compensator 5. In this way, the circuits 22 to 25 and the like constitute a color saturation detection means.

The reason why the difference between the R signal and the remaining color signals is used as the color saturation level is as follows. That is, in general, the proportion of the G filter in the color filter is twice that of the R filter and the B filter. This is because visibility is higher than the G component.

Therefore, since the spatial frequency of the G filter is approximately twice that of the R and B filters,
When the image sensor is scanned, the G sampling frequency is approximately twice the R sampling frequency, and the Nyquist frequency for the G signal is also twice that of the R signal.

That is, the aliasing distortion as described above is most noticeable for the R component, and is also likely to occur for low spatial frequencies.

Note that the B component has low visibility and moiré and the like are relatively inconspicuous, so it can be ignored.

Based on this idea, as a guideline for color saturation,
It is sufficient to detect the ratio of the R component to the Y component or the level of (RY).

It is clear from the above reasons that if this is further simplified, the ratio or difference between the R component and the G component may be used.

The point is to compare the R component with other main color components.

FIG. 5 is a diagram showing a second embodiment of the present invention from this point of view. That is, this is an example in which the level of the (RG) signal as the output of the subtracter is used as the color saturation level.

Further, in the embodiment shown in FIG. 3, the color difference signals are R-G, B.
-G, but the color difference signals are R-Y, B-
In a system that uses Y, (RY) of these
It is obvious that the signal may also be used as a color saturation signal.

Further, although the third illustrated embodiment shows an example using R, G, and Cy filters, the present method also holds true when R, G, and B filters are used.

FIG. 6 shows a row of contour compensators 5 according to the invention. The contour compensator shown in figure a has the frequency characteristics shown in figure b, and the amount of compensation is determined by the voltage variable resistance.
Since it is proportional to the ratio between R _L and the emitter resistance R _E of the differential amplifier, it is possible to control the high frequency component of the input signal e _i .

That is, in the contour compensator of FIG. 6a, the input signal
The output signal e _p for e _i is e _p =−e _i e ^-j 〓・A {1+B(1−cosθ)} (A=R _M /R _E , B=R _E /R _L , θ=wτ ) holds, the value of voltage-controlled variable resistor R _L changes with control voltage V _C3 , which changes the value of B, and the gain at frequency 1/2τ changes as shown in Figure 6b. . Therefore, if the level of the control signal V _C3 is higher, that is, the color saturation is higher, the resistor R _L is made larger, so that the outline is rounded and the high frequency components are restricted, making it difficult for aliasing distortion to occur. Note that D _L in FIG. 6a is a delay line having a delay amount τ (nsec), and B ₁ <B ₂ in FIG. 6b. 7th
Figure a shows a third embodiment of the present invention. In this embodiment, an edge detector detects a contour signal from the color saturation detection signal V _C , and the contour compensator 5 is controlled by this detection signal. That is, the edge detector 35 extracts the contour signal R ₁ from the color saturation detection signal V _C , and the next stage slicing circuit 36 adjusts the contour signal R ₁ to negative polarity and then slices it to a predetermined level. The above contour signals are obtained.

This is not only to detect the color saturation level using the R-G signal, but also to correct the band of the luminance signal for edge portions where moiré is particularly likely to occur. Then, the signal _R2 of the edge portion detected in this way is added by an adder 37 to the output _YL of the low-pass filter 2' for extracting the low-frequency components of the low-pass filter 2 shown in FIG.
Form V _C4 . This V _C4 signal changes the frequency characteristics of the contour compensator 5'. In this case, the configuration of the contour compensator 5' is basically the same as that shown in FIG. 6a, and the value of the voltage-controlled variable resistor R _L is set to increase as the level of the control signal V _C4 decreases.

As a result, high-frequency components of the luminance signal are suppressed, especially in edge portions when color saturation is high.

Furthermore, even when the level of the luminance signal becomes low, the high frequency components of the luminance signal are suppressed, so random noise contained in the high frequency components is reduced and the S/N ratio is improved.
In this embodiment, the luminance signal band is limited by detecting edges of the R-G signal and R-Y signal that indicate color saturation, but in addition to these, the R-Y signal and R-Y signal - The high-frequency component of a signal indicating color saturation, such as a G signal, may be extracted using a high-pass filter, and the luminance signal band may be limited according to this level.

(Effects) As detailed above, according to the present invention, color and
In a solid-state imaging device using a color filter in which color filters are arranged periodically, such as a stripe filter, aliasing distortion does not occur even when imaging a subject with high color saturation, and good image quality is always obtained. I can do it.

Further, it is convenient because the configuration is simple and it can be used also as part of a conventional signal processing circuit (for example, a contour compensator).

Further, since the color saturation detection method is extremely simple, manufacturing is easy, and a part of the output of the signal processing circuit can be used as is.

In addition, since the luminance signal band is limited by the level of the high frequency portion (edge portion) of the color saturation detection signal, high frequency energy such as the edge portion of an image with high color saturation is likely to cause aliasing distortion. Since the band is limited to only the part where the components are concentrated, it has many effects such as a very large effect of reducing aliasing distortion.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the configuration of a striped filter according to the present invention, FIG. 2 is a diagram explaining the balance effect, FIG. 3 is a block diagram showing the configuration of an embodiment of the present invention, and FIG. 4a , b are diagrams showing the output of the color saturation detection circuit according to the invention, FIG. 5 is a diagram showing the main part configuration of the second embodiment of the imaging device of the invention, and FIG.
Figure a shows an example of the configuration of a contour compensator, Figure b
7a is a diagram showing the frequency characteristics of the imaging device, FIG. 7a is a diagram showing the configuration of the third embodiment of the imaging device of the present invention, and FIG.
is a diagram showing the main part signal waveform. 1...Image sensor, 2...Low pass filter, 5...Contour compensator, 23...DC amplifier, 2
4...Slice circuit, 35...Edge detection circuit.

Claims (1)

[Scope of Claims] 1. Imaging means for converting a subject image into an electrical signal; Signal processing means for forming a plurality of color signals including at least a red signal and a luminance signal from the electrical signal; Compensating the outline of the luminance signal. and an arithmetic means for calculating a level difference or ratio between the red signal and the brightness or a signal corresponding to the brightness, the frequency of the contour compensating means being adjusted according to the calculation result of the arithmetic means. An imaging device configured to control characteristics.