JPS63288575A - Image pickup device - Google Patents

Abstract

PURPOSE:To prevent a false color generating in a chrominance signal and to enlarge the dynamic range of the chrominance signal by controlling the dynamic range of the respective element signals of an image pick-up element before a color separation according to a color temperature. CONSTITUTION:By using a color temperature signal STC obtained from a color temperature detecting circuit 47, clip values SCW-SCYe optimum to the color temperature at that time are obtained with a clip operating circuit 48. By these optimum clip values, respective element signals SG-SYe are clipped 37-40. Thus, when a white subject is photographed and an incident light quantity is over an L2, a false color is not generated in signals SR3-SB3 color-separated 41. Thus the false color is not generated in a chrominance signal and the dynamic range of the chrominance signal can be enlarged.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an imaging device used as a color video camera, television camera, or the like.

BACKGROUND OF THE INVENTION As a photoelectric converter (that is, an image sensor) in a conventional imaging device, an image pickup tube and, in recent years, a solid-state image sensor are often used. To obtain color image signals using these image sensors, the subject image focused by a lens is separated into three primary colors using a prism and a dichroic mirror, and each is photoelectrically converted using a different image sensor to produce the three primary colors. A method for obtaining signals (three-tube type, three-plate type) and a mosaic color filter are provided on the light-receiving surface of one image sensor, and spatial color modulation is applied to the image of the object formed on the light-receiving surface. A method (single tube type/single plate type) was mainly adopted in which color signals such as the three primary colors or color differences are obtained by processing the output signal of the image sensor.

There are various types of color filters used in single-tube and single-plate types, but they can be broadly classified into primary color type and complementary color type. This is the difference between using primary colors or complementary colors in the color filter, and each
Primary color filters have good color reproduction, and complementary color filters have good sensitivity and brightness resolution. However, in either method, when a high-brightness subject is imaged, false colors may occur due to differences in the dynamic range of pixels of each color. If a pixel of one color is saturated but a pixel of another color is not, the color signal separated from these pixel signals is
This was inconvenient in that it resulted in a signal that was a different color from the original color.

As a conventional imaging device equipped with a white clip to reduce this false color, for example, Japanese Patent Laid-Open No. 61-19898
The configuration shown in Publication No. 9 is known.

FIG. 9 is a block diagram showing the configuration of this conventional imaging device, in which 1 is an imaging optical system, 2 is an imaging device (hereinafter referred to as COD), 3 to 6 are sample and hold circuits, and a 7Fi brightness band low-pass filter. (hereinafter referred to as LPF), 8 to 1o
is a color band ronos filter (hereinafter referred to as LPF),
11 is a luminance (Y) process circuit, 12 is a red (R) process circuit, 13 is a green (G) process circuit, 14 is a blue (B) process circuit, 16 is a matrix circuit for synthesizing color difference signals, and 16 is a composite television This is an encoder that synthesizes video signals.

The color temperature detection circuit 17 detects light around the subject and generates a color temperature signal ST based on the ratio of the red component to the blue component therein.
This color temperature signal STC is
Process circuit 12. It is added to the B-pro upper 2 circuit 14 to perform white balance. In addition, the level conversion circuit 1
8 is the R process circuit 12.8 from the color temperature signal STC. G
Process circuit 13. It generates a signal SWC for setting the white clip level of the B-pro upper 2 circuit 14.

The operation of the conventional imaging device configured in this manner will be described below.

The subject image is formed on C0D2 via the imaging optical system 1,
It is photoelectrically converted and read out sequentially. The image signal SCC obtained from the read output is sampled and held by four sample and hold circuits 3 to 6. the result,
It is separated into a luminance signal SY, a red signal SR, a green signal SG, and a blue signal SH. The luminance signal SY passes through LPF7 and Y
It is processed by the process circuit 11 and input to the encoder 16 as a luminance signal SY1. Red signal SR.

LPF corresponding to green signal SG and blue signal SB respectively
8 to 10, and the R process circuit 12. G process circuit 13. After being processed by the B-pro upper two circuits 14, the new red signal SR1, green signal SG1. Blue signal S
It is supplied to the matrix circuit 15 as B1. This matrix circuit 16 generates two color difference signals 5DRY and ! of (RY) and (B-Y). 9 DBY are combined and input to the encoder 16. The encoder 16 outputs the luminance signal SY1. A composite television signal SVD is synthesized from the same color difference signals 5DRY and 5DBY based on a synchronization signal, and is output from a video output terminal TVD.

@Figure 10 is a configuration diagram of C0D2 in Figure 9.

Here, 21 is a color filter with an RGB stripe arrangement.
22 is a pixel that performs photoelectric conversion, 23 is a vertical transfer CCD, 2
4 transfers the charge in the pixel 22 to the vertical transfer CCD 23;
25 is a horizontal transfer COD, 26 is a second transfer gate that transfers the charge of the vertical transfer CCD 23 to the horizontal transfer C0D2ts, and 27 is an amplifier that converts the charge into a voltage.

Since the color filter 21 has an R, G, and B stripe arrangement, the output from the amplifier 27 is taken out in 11 order of R, G, and B.

Figure 11 shows the C0D obtained when imaging a white subject.
FIG. 2 is a characteristic diagram showing the relationship between each color output of No. 2 and the color temperature of a light source illuminating a subject. The ratio of each color component of light obtained from a white object changes as shown by the R, G, and B curves in the figure. However, in a normal image sensor, the sensitivity of B is low, and outputs of the R, G, and B' curves in the figure are obtained. The dynamic range of each color is inversely proportional to its respective sensitivity, so especially at low color temperatures, e.g. The dynamic range of H decreases below.

FIG. 12 is an input/output characteristic diagram of the level conversion circuit 18.

The color temperature signal STC is roughly given by the following formula: 5TC=/Tc (k is a constant) −・−・−−−
-(1) where k is a constant and To is a color temperature.

Therefore, 'ro='ro,! :6 When the color temperature is low, the generation of false colors can be prevented by lowering the level of the white clip signal SWC and lowering the color dynamic range.

FIG. 13 is a block diagram showing the configuration of the R process circuit N12. Here, 121 is a clamp circuit, 122 is a variable gain amplifier that performs white balance, 123 is a gamma correction circuit, 124 is a white clip circuit, and 126 is a blanking circuit.

The input signal output from the LPF 8 is first clamped by a clamp circuit 121, and the gain is controlled by a variable gain amplifier 122 according to the color temperature signal STC to perform white balance. After gamma correction in the gamma correction circuit 123 at the next stage, white clipping is performed in the white clip circuit 124 with a voltage according to the white clip signal SWC.

Thereafter, the blanking circuit 126 blanks the signal and outputs it as a red signal SR1. B Pro upper 2 circuits 1
4 is similarly configured.

Problems to be Solved by the Invention However, as described above, the configuration in which white clipping is performed after color separation into R, G, and B has the following problems1) Furthermore, Fig. 14 The incident light in a single-chip color camera using a primary color filter type image sensor is seven Y, R, G,
Figure 15 is a characteristic diagram showing the relationship between the amount of incident light and the output of Y, R, G, and B in a single-chip color camera using a complementary color filter type image sensor. 1) In the primary color filter method, R, Q, and B pixel signals become saturated when the amount of incident light exceeds their respective dynamic ranges. Therefore, by setting the white clip level of the color processing circuit to a level lower than the incident light @L, it is possible to prevent the occurrence of false colors.

However, as shown in FIG. 15, in a single-chip color camera using a complementary color filter type image sensor, the amount of incident light is limited. If it exceeds , the color-separated color signal will conversely decrease. In such cases, the white clip level of the color process circuit is measured by the incident light level. Even if it is set to a lower value, if the amount of incident light becomes larger, the R and B signals will become smaller than the white clip level, and therefore cannot be clipped, resulting in false color.

SUMMARY OF THE INVENTION In view of these problems, it is an object of the present invention to provide an imaging device that does not generate false colors even for high-luminance signals and has a large dynamic range of color signal system.

Means for Solving the Problems In order to achieve the above object, the imaging device of the present invention includes a color temperature detection circuit that detects the color temperature of object illumination, and a color temperature detection circuit that detects the color temperature of the object illumination, and a color temperature detection circuit that detects the color temperature of the object illumination. The present invention is characterized in that it includes a clip circuit that limits the level of a pixel signal, and the clip value of the clip circuit is controlled by the output signal of the color temperature detection circuit.

Effect With the above configuration, by controlling the dynamic range of each pixel signal of the image sensor according to the color temperature before color separation, false colors do not occur in the color signal obtained by separating each pixel signal. At the same time, it expands the dynamic range of color signals over a wide range of color temperatures.

EXAMPLES Hereinafter, examples of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an imaging device according to a first embodiment of the present invention.

In FIG. 1, reference numeral 31 is an optical system that forms an optical image of a subject (not shown) on the image sensor 32, and 33 to 36 are sample and hold circuits. The pixel signal of each color of the output signal SCC is sampled and held. 37~
40 is the output signal S of the sample and hold circuits 33 to 36
W, S.G.

This is a clipping circuit that clips SCy and SYe at a clip value according to a control signal input to the control side.

41 is the output signal SW1°S of the clip circuits 37 to 4o
This is a color separation circuit that separates color signals from G1, 5Cy1, and 5Ye1. 42 is the output signal b of the image sensor 32
43 is a luminance (Y) process circuit that performs gamma correction etc. on the luminance signal; 44 is the output signal SR2, SG2 . . . of the color separation circuit 41; SB2 is a color processing circuit that performs processing such as white balance and γ correction, and 45 is an output signal SR3, SG3 . A matrix circuit 46 generates a color difference signal from SB3, and a composite television signal SVD is generated from the output signal SY of the luminance (Y) process circuit 43 and the output signals 5DRY (R-Y) and 5DBY (B-Y) of the matrix circuit 45. This is an encoder that synthesizes the video and outputs it to the video output terminal. 47 is a color temperature detection circuit that detects the color temperature of a light source illuminating a subject (not shown);
48 is W(
white), G (green), c7 (cyan),
This is a clip value calculation circuit that calculates clip values for each color of Ye (yellow), and the output signals SCW, SCG, 5CCy, and 5CYe of this clip value calculation circuit 48 are
are input to the control side of the clip circuits 37 to 4o, respectively.

FIG. 2 shows the color filter array of the image sensor 32.

According to this color filter, W and G are alternately output on odd-numbered scanning lines, and Cy and Ye are output on even-numbered scanning lines. In order to separate the luminance signal from this color filter, it is sufficient to use an LPF 42 having a band of % of the pixel sampling frequency. Further, in order to separate the R, G, and H color signals, the color separation circuit 41 calculates the following equation.

R=W-C7... (2) B=W-Ye
(3) FIG. 3 is a block diagram showing the configuration of a clip value calculation circuit 48 constructed using a microprocessor.

In FIG. 3, 51 is an A/D converter that converts the color temperature signal STC into a digital quantity; 52 is a microprocessor that calculates the clip level of each pixel signal based on the A/D converted color temperature signal; 63 is a microprocessor 62
The clip level calculated by is converted into analog amounts SCW and SCG.
, 5CCy, 5CYe and clip circuits 37 to 4
This is a D/A converter that outputs to 0.

The operation of the clip value calculation circuit 48 configured as described above will be explained using a block diagram showing an equivalent function. FIG. 4 is an equivalent block diagram of the clip value calculation circuit.
1 takes the color temperature signal STC as input and outputs W according to the STC.
This is a W function table that outputs the clip value of a (white) pixel. 62 to 64 are Gt'A number tables that output clip values of G (green), Cy (cyan), and Ye (yellow) pixels, respectively, similar to the W function table e1.

They are a cy function table and a Ye function table. FIG. 6 is a characteristic diagram showing the input/output relationship of these function tables. This is the output value of each pixel when W is saturated when a white subject is photographed.

However, these curves differ depending on the spectral characteristics of the color filter and the spectral sensitivity characteristics of the photoelectric conversion element of the image sensor. By providing the function tables 61 to 64 with the characteristics shown in FIG. 6, the clip levels SCW, SCG, 5CCy
, 5CYe are output.

If the processing of referring to these function tables is performed by the microprocessor 52 shown in FIG. 3, clip level calculations can be performed very easily and accurately with good reproducibility.

Regarding the imaging device of this embodiment configured as described above,
The operation will be explained below.

FIG. 6 shows the relationship between the amount of incident light and the pixel output of the image sensor 32. (&) indicates (C) when the color temperature of the subject illumination is low.
(b) is a case where the color temperature is between (-) and (c).

As mentioned above, pixels with high sensitivity have a narrow dynamic range (W saturates most quickly).

When W becomes saturated, as can be seen from equations (2) and (3), the separated R and B will take on incorrect values, thus causing false color. In other words, the incident scene L2 where W is saturated
If the pixel signals of each color are clipped with , false colors will not occur. However, since this clip value changes depending on the color temperature of the subject illumination, the clip value calculation circuit 48 uses the color temperature signal STC obtained from the color temperature detection circuit 47 to determine the lip value 5CW-5CYs that is optimal for the color temperature at that time. If you clip each pixel signal, the color-separated (after white balance) signals SR3 to SB3 will be as shown in Figure 8 when a white subject is photographed, and the incident light amount will be L.
Even if it exceeds 2, false color does not occur.

As described above, according to this embodiment, the clip level of the pixel signal of the image sensor is calculated and controlled by determining the sensitivity of each pixel according to the color temperature, and the auxiliary filter method is used. Even when capturing images of high-brightness objects with a camera, it is possible to obtain color signals with the widest dynamic range and without false colors.

In the above embodiment, the color filter of the image sensor 32 is of the type shown in FIG. 2, but a filter using other colors may be used. Of course, the image sensor 32 may be a solid-state image sensor or an image pickup tube. Further, although the output signal SCC of the image sensor 32 is used as the brightness signal, the output signals SW1 to 5Ye1 of the clip circuits 37 to 40 may be used. Although the color temperature is detected by a color temperature detection circuit, a gain control signal of a white balance circuit that controls the average value of color difference signals to be O may also be used. Furthermore, the clip level of each pixel signal may be set slightly higher than the dynamic range L2 of the element, within a range where the occurrence of false colors does not cause any visual problem. Also W(
White) clip circuit 37. The W function table 61 can be omitted by using W (white) as the reference for clipping or calculation of each color.

Effects of the Invention According to the present invention, there is provided a color temperature detection circuit that detects the color temperature of object illumination, a clip circuit that limits the level of a pixel signal of an image sensor before separating color signals based on a control signal, and Since the configuration includes a clip value calculation circuit that outputs a control signal that variably controls the clip value of the clip circuit based on the output signal of the color temperature detection circuit, even if an auxiliary filter type image sensor is used, The dynamic range of each pixel signal is controlled so that false colors do not occur in the color signal obtained by separating each pixel signal. At the same time, it is possible to expand the dynamic range of color signals over a wide range of color temperatures.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an imaging device according to an embodiment of the present invention, FIG. 2 is a configuration diagram showing a color filter arrangement of an image sensor of the imaging device, and FIG. 3 is a clip value calculation of the imaging device. A block diagram showing the configuration of the circuit; FIG. 4 is an equivalent block diagram explaining the operation of the clip value calculation circuit shown in FIG. 3;
Fig. 6 is a diagram showing the input/output characteristics of the function table in Fig. 4, and Figs. 7 is a characteristic diagram showing the relationship between the incident light amount of the image sensor of the imaging device and the output of the clipping circuit, and FIG. 8 is a characteristic diagram showing the relationship between the incident light amount and the color-separated three primary color signals. FIG. 9 is a block diagram showing the configuration of a conventional imaging device;
Fig. 10 is a configuration diagram of a COD in a conventional imaging device, Fig. 11 is a characteristic diagram showing the relationship between each color output obtained when photographing a white subject with the same COD and the color temperature of the subject illumination, and Fig. 12 is a FIG. 13 is an input/output characteristic diagram of a level conversion circuit in a conventional imaging device; FIG. 13 is a block diagram showing the configuration of an R process circuit in a conventional imaging device;
151 is a characteristic diagram showing the relationship between the incident light amount of the image sensor of the primary color filter and the color-separated three primary color signals, and FIG. It is a diagram. 31...Optical system, 32...Image sensor,
33~34...Sample hold circuit, 37~
4o... Clip circuit, 41... Color separation circuit, 42... Luminance low pass filter, 43
...Brightness process 1 [! 1st road, 44th...
Color process circuit, 45...Matrix circuit, 4
6...Encoder, 47...Color temperature detection (i11 path, 48...Clip value calculation circuit. Name of agent: Patent attorney Toshio Nakao, 1st person) 2
Fig. 3 L -----J Fig. 4 Fig. 5 Fig. 6 Amount of charge to "' Fig. 7

Claims (1)

[Claims] a color temperature detection circuit that detects the color temperature of object illumination; a clip circuit that limits the level of the image signal of the image sensor before color signal separation based on the control signal; and a clip circuit that limits the level of the image signal of the image sensor before color signal separation based on the control signal; An imaging device comprising: a clip value calculation circuit that outputs a control signal that variably controls a clip value of the clip circuit.