JP2001189945A - Image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid a change in a hue due to processing an image signal by decreasing the saturation and to prevent production of a color noise, caused by a noises which are different by each pixel. SOLUTION: A color difference gain calculating circuit 9 calculates color difference gain for changing the saturation on the basis of R, G, B signals fed from a color separation circuit 7. A color difference multiplier circuit 11 multiplies the color difference gain, calculated by the color difference gain calculation circuit 9 with a color difference signal supplied from a YC matrix circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image pickup apparatus that makes inconspicuous high and low luminance colors generated by signal processing inconspicuous.

[0002]

2. Description of the Related Art In a conventional digital still camera, video camera, or the like, an analog image signal from an image sensor is once digitized, and signal processing such as white balance and gamma correction is performed on the digitized image signal. Have been done.

Next, a conventional imaging apparatus for performing such signal processing will be described. FIG. 5 shows a conventional imaging device.

As shown in FIG. 5, a conventional image pickup apparatus 100 includes a CCD (Charge Coupled Device) 101,
CDS (Co-related Double Sampling) 102 and A /
A D conversion circuit 103, a white balance circuit 104,
Gamma correction circuit 105, color separation circuit 106, YC matrix circuit 107, and knee circuit 108
And

The CCD 101 has R (red), G
This is a solid-state image sensor in which color filters of a color array of (green) and B (blue) are arranged, and converts light incident through a lens (not shown) into an image signal, which is an electric signal, and converts the light into a CDS 102
To supply. When the CCD 101 is a single-plate type, the imaging signals of each color according to the arrangement of the color filters for each pixel are sequentially output in a multiplexed form on one output line.

The CDS 102 performs a correlated double sampling process on the image pickup signal supplied from the CCD 101 and converts the correlated double sampled image signal into an A / D signal.
It is supplied to the conversion circuit 103.

The A / D conversion circuit 103 converts the image signal supplied from the CDS 102 into a digital image signal and supplies the digital image signal to a white balance circuit 104.

[0008] The white balance circuit 104 adjusts the white balance of the digital image signal supplied from the A / D conversion circuit 103, and supplies the adjusted image signal to the gamma correction circuit 105. The white balance circuit 104 is a circuit that adjusts the sensitivity of the CCD 101 for each color of RGB to achieve white balance.

The gamma correction circuit 105 performs a gamma correction process on the white balance adjusted image signal supplied from the white balance circuit 104, and supplies the gamma corrected image signal to the color separation circuit 106.
The gamma correction circuit 105 is a non-linear circuit for correcting the gamma characteristic of a monitor (not shown), and has a knee characteristic in a high-luminance portion to secure a wide dynamic range.

The color separation circuit 106 includes a gamma correction circuit 10
5 is subjected to pixel interpolation processing on the gamma-corrected image signal supplied from
A signal and an image signal of a B signal are generated. Color separation circuit 106
Supplies the generated R, G, and B image signals to the YC matrix circuit 107.

The YC matrix circuit 107 converts the image signal composed of the R, G, and B signals supplied from the color separation circuit 106 into a luminance signal (Y) and color difference signals (Cb, Cb).
r). The YC matrix circuit 107 supplies the converted luminance signal to the knee circuit 108. The YC matrix circuit 107 outputs the converted color difference signal.

The knee circuit 108 performs a knee process on the luminance signal supplied from the YC matrix circuit 107 in order to improve coloring in a high luminance portion. Then, the knee circuit 108 outputs the luminance signal after the knee processing.

The conventional imaging apparatus 1 configured as described above.
In 00, the luminance signal output from the knee circuit 108 and the chrominance signal output from the YC matrix circuit 107 are then recorded, for example, in a JPEG-compressed recording medium (not shown) or via an encoder such as NTSC or PAL. Video output.

[0014]

By the way, in the gamma correction circuit 105 provided in the conventional imaging apparatus 100, the image signal composed of the input R (red) signal, G (green) signal, and B (blue) signal Is subjected to gamma correction processing. However, even if the gamma correction circuit 105 is used, the gamma characteristic of the monitor cannot be completely corrected. Particularly on the high luminance side, the knee characteristic is provided to secure a wide dynamic range, and the limitation of the output dynamic range on the circuit causes the gamma correction characteristic obtained by the gamma correction circuit 105 to be as shown in FIG. As shown by d in the figure, the curve deviates from the ideal γ correction curve.

If the R signal, G signal, and B signal are at the same signal level, there is little problem. However, when the respective signals have different signal levels, that is, when the signals are colored signals. In some cases, knee characteristics may or may not be applied to each signal. As a result, when a subject having the same color is photographed with a different brightness, not only the brightness but also the color changes, and the quality of the image is significantly impaired.

FIGS. 6A to 6C show changes in the balance of the R signal, the G signal, and the B signal when the aperture is opened while photographing a certain subject.

For example, the skin color is RG as shown in FIG.
As the aperture is opened, the output from the gamma correction circuit 105 changes along the γ characteristic shown in FIG. Then, when the aperture is further opened and the brightness becomes as high as b in FIG. 6, it can be seen that only the R signal has a knee characteristic. This means that since the hue is determined by the RGB ratio, if only the R signal changes, the hue changes, that is, the color changes.

When the aperture is further opened and the brightness increases to c in FIG. 6, the output D range (D-ra
n)), the R signal is clipped, and the color changes more severely. That is, since the change of the R signal is smaller than the change of the G signal, the flesh color changes to yellow.

In a low-luminance region, noise due to the dark current of the CCD and the like differs for each pixel, so that there is a problem that the noise appears as color noise. further,
There is also a problem that the noise in the low luminance region is conspicuous because γ stands.

The present invention has been made in view of such circumstances, and it is possible to prevent a change in hue caused by processing of an image signal by reducing saturation, and to prevent color noise caused by different noise for each pixel. It is an object of the present invention to provide an imaging device that prevents occurrence of the image.

[0021]

In order to achieve the above object, an imaging apparatus according to the present invention captures an image and generates an imaging signal including a red signal, a green signal, and a blue signal. Means, a signal conversion means for converting an image signal generated by the image signal generation means into a luminance signal and a color difference signal, and a color difference for changing saturation based on the image signal generated by the image signal generation means. A color difference gain calculating means for calculating a gain, and a color difference multiplying means for multiplying the color difference signal converted by the signal converting means by the color difference gain calculated by the color difference gain calculating means.

In this imaging device, the color difference gain calculating means calculates a color difference gain for changing the saturation based on the image pickup signal, and the color difference multiplying means calculates the color difference gain calculated by the color difference gain calculating means based on the signal. The color difference signal converted by the conversion means is multiplied.

[0023]

Embodiments of the present invention will be described below with reference to the drawings.

An imaging apparatus according to an embodiment to which the present invention is applied is an apparatus using a single-chip CCD (Charge Coupled Device). FIG. 1 shows an imaging apparatus according to an embodiment to which the present invention is applied.

As shown in FIG. 1, the image pickup apparatus 1 has a CCD
2, CDS (Co-related Double Sampling) 3, A
/ D conversion circuit 4, white balance circuit 5, gamma correction circuit 6, color separation circuit 7, YC matrix circuit 8, color difference gain calculation circuit 9, knee circuit 10, and color difference multiplication circuit 11. And

The CCD 2 has R (red), G
This is a solid-state imaging device in which color filters of a color array of (green) and B (blue) are arranged, and converts light incident through a lens (not shown) into an imaging signal, which is an electric signal, and supplies it to the CDS 3. Further, since the CCD 2 is a single-plate type, the imaging signals of each color according to the arrangement of the color filters for each pixel are sequentially output in a form multiplexed (multiplexed) on one output line.

The CDS 3 performs a correlated double sampling process on the image pickup signal supplied from the CCD 2,
A / D conversion circuit 4 converts the image signal after the double sampling processing
To supply.

The A / D conversion circuit 4 converts the image signal supplied from the CDS 3 into a digital image signal, and converts the digital image signal into a white balance circuit 5.
To supply.

The white balance circuit 5 adjusts the white balance of the digital image signal supplied from the A / D conversion circuit 4 and supplies the adjusted image signal to the gamma correction circuit 6. This white balance circuit 5
Is a circuit for adjusting the sensitivity of the CCD 2 for each color of RGB to achieve white balance.

The gamma correction circuit 6 performs gamma correction processing on the white balance adjusted image signal supplied from the white balance circuit 5, and supplies the gamma corrected image signal to the color separation circuit 7. The gamma correction circuit 6 is a non-linear circuit that corrects a gamma characteristic of a monitor (not shown), and has a knee characteristic in a high luminance portion in order to secure a wide dynamic range.

The color separation circuit 7 performs pixel interpolation processing on the gamma-corrected image signal supplied from the gamma correction circuit 6, and performs R signal, G signal, and B signal processing for all the pixels.
Generate an image signal of the signal. The color separation circuit 7 supplies the generated image signals of the R signal, the G signal, and the B signal to the YC matrix circuit 8 and the color difference gain calculation circuit 9.

The YC matrix circuit 8 includes a color separation circuit 7
Is converted into a brightness signal (Y) and color difference signals (Cb, Cr). The YC matrix circuit 8 supplies the converted luminance signal to the knee circuit 10 and supplies the converted color difference signal to the color difference multiplying circuit 11.

The color difference gain calculating circuit 9 calculates a color difference gain based on the image signal composed of the R signal, the G signal, and the B signal supplied from the color separating circuit 7, and multiplies the calculated color difference gain by the color difference multiplying circuit 11. To supply.

The knee circuit 10 includes a YC matrix circuit 8
Is performed on the luminance signal supplied from the device in order to improve the coloring in the high luminance portion. Then, the knee circuit 10 outputs the luminance signal after the knee processing.

The color difference multiplication circuit 11 multiplies the color difference signal supplied from the YC matrix circuit 8 by the color difference gain supplied from the color difference gain calculation circuit 9. And
The color difference multiplying circuit 11 outputs the multiplied color difference signal.

In the imaging apparatus 1 configured as described above,
The luminance signal output from the knee circuit 10 and the chrominance signal output from the chrominance multiplication circuit 11 are, for example, JP
EG compression and recording on a recording medium (not shown)
Video output is performed via an encoder such as TSC or PAL.

Next, the saturation control section including the YC matrix circuit 8, the color difference gain calculation circuit 9, the knee circuit 10, and the color difference multiplication circuit 11 will be described in detail.

In this saturation control section, as shown in FIG.
The YC matrix circuit 8 converts the image signal composed of the R signal, the G signal, and the B signal supplied from the color separation circuit 7 into a luminance signal (Y), and the R matrix signal supplied from the color separation circuit 7. A C matrix circuit 8b that converts an image signal composed of a signal, a G signal, and a B signal into a color difference signal Cb and a color difference signal Cr, and converts the color difference signal Cb and the color difference signal Cr supplied from the C matrix circuit 8b into a color difference band. And the LPF 8c for C that restricts the

The color difference multiplying circuit 11 includes an LPF 8 for C.
a multiplier 11a for multiplying the band-limited color difference signal Cb and the color difference signal Cr supplied from c by the color difference gain supplied from the color difference gain calculation circuit 9, and the multiplier 1a
It has a C MUX (multiplexer) 11b that outputs one color difference signal (Cb, Cr) obtained by multiplexing the multiplied color difference signal Cb and the color difference signal Cr supplied from 1a.

Further, the color difference gain calculating circuit 9 includes a maximum value circuit 9a, an LPF 9b for C, and a high luminance calculating circuit 9c.
And a low-luminance calculation circuit 9d and a minimum value circuit 9e.

First, the maximum value circuit 9a compares the signal levels of the R signal, G signal, and B signal supplied from the color separation circuit 7, and calculates the maximum value of the signal level. Then, the maximum value circuit 9a calculates data on the calculated maximum value,
The R signal, G signal, and B signal are supplied to the C LPF 9b.

The C LPF 9b converts the signal having the maximum signal level among the signals calculated by the maximum value circuit 9a into a color difference band based on the maximum value data supplied from the maximum value circuit 9a. Match. That is, LPF for C
Reference numeral 9b denotes a band limiting filter that limits a final change in gain to a band of color difference. This is because the gain is directly multiplied by the color difference signal supplied from the C matrix circuit 8c, so that the signal must be a low-frequency signal in order to remove noise as a control signal. The LPF 9b for C supplies the high-luminance signal among the R, G, and B signals limited to the color difference band to the high-luminance calculation circuit 9c, and outputs the low-luminance signal to the low-luminance calculation circuit 9c. 9d.

From the visual characteristics of human beings, humans are less sensitive to changes in color than to changes in luminance. Therefore, it is common to compress the output data by limiting the band of the color difference signal. It is a target.

The high luminance calculation circuit 9c calculates the gain of the color difference on the high luminance side based on the signal on the high luminance side supplied from the LPF 9b for C and the characteristic diagram on the high luminance side shown in FIG. 3A. Then, the high luminance calculation circuit 9c supplies the calculated gain of the color difference on the high luminance side to the minimum value circuit 9e.

In the characteristic diagram on the high luminance side shown in FIG. 3A, as shown in FIG.
That is, the level at which the saturation on the high-luminance side begins to drop is set to CSHT.
H, and a high luminance saturation gain (slope), that is, a degree of decreasing the saturation on the high luminance side is CSHG.

The low luminance calculation circuit 9d calculates the gain of the color difference on the low luminance side based on the signal on the low luminance side supplied from the C LPF 9b and the characteristic diagram on the low luminance side shown in FIG. 3c. Then, the low luminance calculation circuit 9d supplies the calculated gain of the color difference on the low luminance side to the minimum value circuit 9e.

In the characteristic diagram on the low luminance side shown in FIG. 3C, as shown in FIG.
That is, the level at which the saturation on the low-luminance side begins to drop is set to CSLT.
H, and the low-luminance saturation gain (slope), that is, the degree of decreasing the low-luminance saturation, is CSLG.

The minimum value circuit 9e calculates the color difference gain on the high luminance side supplied from the high luminance calculation circuit 9c and the color difference gain on the low luminance side supplied from the low luminance calculation circuit 9d. A minimum value of the color difference gain is selected, and the selected minimum value is supplied to the multiplier 11a as a final color difference gain as shown in FIG. 3D.

The multiplier 11a is connected to the LPF 8c for C.
Is multiplied by the color difference gain supplied from the minimum value circuit 9e, and the multiplied color difference signal Cb and color difference signal Cr are supplied to the C MUX 11b. Supply. MUX11 for C
b multiplexes the multiplied color difference signal Cb and the color difference signal Cr supplied from the multiplier 11a, and outputs a single color difference signal (Cb, Cr).

Next, specific processing performed in the saturation control section will be described in detail.

FIG. 4 shows changes in the luminance signal and the color difference signal in the image pickup apparatus 1.

First, on the high-brightness side, the RG
FIG. 4A shows changes in the luminance signal and the color difference signal when the aperture of the signal having the B balance is opened.

In the conventional image pickup apparatus, at the signal level as shown in FIG. 4B, only the R signal has a knee characteristic, but in the image pickup apparatus 1 according to the embodiment to which the present invention is applied, the color difference gain is small. Being squeezed. That is, since the same gain is applied to each of the two color difference signals (Cb, Cr), the saturation control unit changes the saturation instead of changing the hue. Further, even if the signal has a knee characteristic, since the saturation has begun to decrease, the color rotation has become inconspicuous.

When the aperture is further opened and the brightness increases to FIG. 4C, the saturation control section further narrows the color difference gain in accordance with the characteristic shown in FIG. 3D. The signal is clipped due to the limitation of the output dynamic range, and the color turns without being able to follow a further change. However, at this point, the saturation is reduced, and the change in the color rotation is not conspicuous.

Also on the low luminance side, the saturation control unit suppresses coloring by narrowing the color difference gain according to the characteristic shown in FIG. 3c as shown in FIG.
Makes color noise less noticeable.

As described above, in the imaging apparatus 1 according to the embodiment to which the present invention is applied, the color difference gain calculating circuit 9 detects the signal levels of the R signal, the G signal, and the B signal, and
By adjusting the gain of the color difference signal when one of the signal levels enters the knee region, it is possible to prevent the color rotation of the high luminance signal due to the knee or clip.

Further, in the imaging apparatus 1 according to the embodiment to which the present invention is applied, a high luminance portion such as a human face changes to yellow or a color unnatural to a change in sky color due to sunlight. Is reduced, so that the image quality of photographing can be improved.

Further, in the imaging apparatus 1 according to the embodiment to which the present invention is applied, the color noise due to the influence of the CCD and the circuit is reduced by adjusting the gain of the color difference signal in the low luminance portion to lower the saturation. be able to.

[0059]

As described above, according to the imaging apparatus of the present invention, the color of the high luminance portion changes, and the color change due to natural light is mixed with the unnatural color change. Therefore, image quality can be improved.

Further, according to the imaging apparatus of the present invention, the color noise caused by the influence of the solid-state imaging device and the circuit can be reduced by lowering the saturation in the low luminance portion.

[Brief description of the drawings]

FIG. 1 is a block diagram of an imaging apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram of a saturation control unit in the imaging device according to the first embodiment.

FIG. 3 is a diagram for explaining a transfer characteristic of saturation control.

FIG. 4 is a diagram for explaining changes in a luminance signal and a color difference signal in the imaging device according to the embodiment of the present invention.

FIG. 5 is a block diagram of a conventional imaging apparatus.

FIG. 6 is a diagram for explaining a cause of color rotation in a conventional imaging device.

[Explanation of symbols]

1 imaging device, 2 CCD, 3 CDS, 4 A / D conversion circuit, 5 white balance circuit, 6 gamma correction circuit, 7 color separation circuit, 8 YC matrix circuit, 9
Color difference gain calculation circuit, 10 knee circuit, 11 color difference multiplication circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C066 AA01 BA20 CA07 CA08 DA05 DC06 DD07 EA03 EA14 EB01 EB03 EC05 EC12 EE03 GA01 GA02 GA05 KA12 KD07 KE03 KE04 KE19 KG01 KM02

Claims (4)

[Claims] An image is taken and a red signal, a green signal,
An imaging signal generation unit configured to generate an imaging signal including a blue signal; a signal conversion unit configured to convert the imaging signal generated by the imaging signal generation unit into a luminance signal and a color difference signal; and an imaging signal generated by the imaging signal generation unit. A color difference gain calculator that calculates a color difference gain for changing the saturation based on the imaging signal; and a color difference gain calculated by the color difference gain calculator is multiplied by the color difference signal converted by the signal converter. An imaging apparatus comprising: a color difference multiplying unit. 2. The color difference gain calculating means, comprising: a maximum value calculating means for calculating a signal having a maximum signal level from among red, green, and blue signals generated by the imaging signal generating means. The imaging device according to claim 1, further comprising: calculating the color difference gain based on a calculation result calculated by the maximum value calculation unit. 3. The high-luminance calculation means for calculating a high-luminance color difference gain based on the calculation result calculated by the maximum-value calculation means, and the maximum-value calculation means Based on the calculated result, a low-luminance calculation means for calculating a low-luminance color difference gain, and a color difference gain calculated by the high-luminance calculation means,
Minimum value selecting means for selecting a color difference gain having a minimum value from the color difference gain calculated by the low luminance calculating means, and the color difference gain based on the minimum value color difference gain selected by the minimum value selecting means. The imaging apparatus according to claim 2, wherein a color difference gain for changing the degree is calculated. 4. The imaging apparatus according to claim 1, wherein the color difference gain is band-limited to a frequency band of a color difference signal.