JP2557620B2 - Imaging device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an imaging device.

[Prior art]

For example, the imaging device is widely used as a television camera. Consumer television cameras are required to have light weight, small size, and low power consumption. Therefore, a solid-state image sensor such as CC
An image pickup device using an image pickup element of a system such as D or MOS is expected as a suitable one. In particular, as a so-called single-chip color camera that captures a color image by using a single solid-state image sensor, many methods have been conventionally proposed.

A camera using a solid-state image sensor has the following features in image quality as compared with a single-tube camera.

There is little geometric distortion.

Good sensitivity flatness.

Good linearity of incident light quantity and output.

Since the output for each pixel can be taken out accurately in synchronization with the drive clock, the degree of color separation is good.

These characteristics appear as an actual image, particularly good color reproducibility. Therefore, the following features are included.

B) Little change in hue due to change in brightness.

B) Little color shading.

C) False colors are less likely to occur in high brightness areas.

By the way, the following is a description of (3) that the above-mentioned characteristics c) the occurrence of false colors in a high-luminance portion is unlikely to occur.

FIG. 1 shows the change characteristics of the incident light amount L and the output D of luminance (Y), red (R), and blue (B) in a television camera of a single tube type, particularly a frequency separation type. As can be seen from this, the output of the R and B color signals decreases in contrast to the increase of the incident light amount in the portion where the light is incident on the light near the point Lo of a specific incident light or more. In the single tube system, since the green (G) output is produced from the Y output, a so-called highlight green phenomenon occurs in which a false color of green is generated in a portion where the incident light amount Lo point or more is incident.

FIG. 2 shows the relationship between the amount of incident light and the outputs D of Y, R, G, and B in a single plate type color camera using a solid-state image sensor. When incident light with a certain amount L or more of incident light hits, R of the color signal reaches the saturation level, so that a cyan false color occurs. However, since the color signal does not decrease as in the first (single tube method), the amount of false color generated is small. Further, if the white clip level of the circuit system is set to a position lower than the incident light amount L, no false color will occur. This will be described below.

FIG. 3 shows the output characteristics of the image sensor output of FIG. 2 after white balance is performed by the signal processing circuit.
For example, if the light source that illuminates the subject is a halogen bulb that is commonly used for color imaging (color temperature 3200 ° K), the output of the solid-state image sensor will differ depending on the method, but generally R: G: B = 1.5: 1: It will be about 0.7. At this time, in the process output after the white balance, the saturation level has this inverse ratio and becomes P _R , P _G , and P _{B in} FIG. here,
It can be seen that the clip point of the process circuit can be set to P _R to maximize the color dynamic range.

As can be seen from the above, in a television camera using a solid-state image sensor, the occurrence of false color in a high-luminance subject is small. Also, the setting of the clip point of the process circuit is
This is an important point in preventing the occurrence of false color. by the way,
The level at which this false color starts to occur depends on the ratio of each color component in the light source that illuminates the subject, and particularly when the color temperature is extremely high, the saturation level of the B output becomes small, and when it is low, the saturation level of the R output becomes small. .

In the conventionally proposed solid-state image pickup television camera, the white clip level of the process circuit is fixed or manually variable. There, the level is set so that false color does not occur even under the worst conditions, or readjustment is performed for each shooting condition. In the case of the fixed type, there is a drawback that the dynamic range of colors becomes narrow. Further, in the case of the variable type, there is a problem that it is not suitable for a consumer camera. Especially in recent years, users (photographers)
In order to reduce the number of operations, there have been proposed many methods without a color temperature conversion filter. In this case, the fixed type has a problem that the color dynamic range is further narrowed.

[Object of the Invention]

The present invention has been made in view of the above problems, and an object of the present invention is to provide an imaging device having a wide color dynamic range.

〔Example〕

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below based on embodiments shown in the drawings.

FIG. 4 shows an embodiment of the present invention. Here, 11 is an image pickup optical system, 12 is a CCD of an image pickup device, 13 to 16 are sample hold circuits, 17 is a luminance band low-pass filter, 18 to 20 are color band low-pass filters, and 21 is a luminance (Y) process circuit. , 22 is a red (R) process circuit, 23 is a green (G) process circuit, 24 is a blue (B) process circuit, 25 is a matrix circuit for combining color difference signals, 26 is an encoder for combining composite television signals, and 27 is A color temperature detection circuit for detecting the color temperature of a subject (not shown), and 28 is a level conversion circuit for producing a white clip signal SWC from the color temperature signal STC.

The subject image is formed on the CCD 12 via the photographing optical system 11,
It is photoelectrically converted and sequentially read. The image pickup signal SCC obtained by the read output is the four sample hold circuits 13 to 1
Sampled and held by 6. As a result, the luminance signal S
It is separated into Y, red signal SR, green signal SG and blue signal SB.
The luminance signal SY passes through the LPF 17, is processed by the Y process circuit 21, and is input to the encoder 26 as the luminance signal SY1. LPF1 that also supports red signal SR, green signal SG and blue signal SB
After passing through each of 8 to 20 and processed by the R process circuit 22, the G process circuit 23, and the B process circuit 24, a new red signal SR1, green signal SG1, and blue signal SB are added.
It is supplied to the matrix circuit 25 as 1. By the matrix circuit 25, the two color difference signals SDRY and SDBY of (RY) and (BY) are combined and input to the encoder 26. The encoder 26 synthesizes the composite television signal SVD on the basis of the input luminance signal SY1, both color difference signals SDRY, SDBY and a synchronizing signal from a clock circuit (not shown), and outputs it from the video output terminal TVD.

The color temperature detection circuit 27 detects light around the subject and generates a color temperature signal STC based on the ratio of the red component and the blue component in the light. The color temperature signal STC is applied to the R process circuit 22 and the B process circuit 24 to perform white balance.
In addition, the level conversion circuit 28 receives the R process circuit 22, the G process circuit 23, and the B process circuit from the color temperature signal STC.
Generates signal SWC that sets 24 white clip levels.

FIG. 5 is an explanatory diagram of the CCD 12 in FIG. Here, 101 is a color filter of R, G, B stripe arrangement, 10
2 is a pixel for photoelectric conversion, 103 is a vertical transfer CCD, 104 is a transfer gate 1 or 1 for transferring charges in the pixel 102 to the vertical transfer CCD 103.
Reference numeral 05 is a horizontal transfer CCD, 106 is a transfer gate 2 for transferring the charges of the vertical transfer CCD 103 to the horizontal transfer CCD 105, and 107 is an amplifier for converting the charges into a voltage. Since the color filter 101 is an R, G, B stripe array, the R, G, B dots are taken out from the output of the amplifier 107 in order.

FIG. 6 is an explanatory diagram for producing Y, R, G, B signals from the output of the CCD 12. As described above, the signal (imaging signal SCC) is output from the CCD 12 in the R, G, and B dot-sequential order corresponding to the filter. The luminance signals Y and the color signals SR, SG and SB of the R, G and B signals are extracted by the sample and hold circuits 13 to 16 by the respective pulses of the sample and hold signals SHR, SHG and SHB.

FIG. 7 shows the relationship between each color output of the CCD obtained when a white subject is photographed and the color temperature of the light source that illuminates the subject. The ratio of each color component of light from a white subject is R,
It changes as shown in G and B. However, in a normal image pickup device, the sensitivity of B is low, and the output of each curve of R, G, B shown in the figure can be obtained. Since the dynamic range of each color is inversely proportional to the sensitivity, the dynamic range of R decreases especially at a low color temperature, for example, To or lower.

FIG. 8 shows the input / output characteristics of the level conversion circuit 28. The color temperature signal STC is generally given by the following equation.

Here, k represents a constant and T _C represents color temperature. Therefore, when the color temperature is lower than T _C = To, it is possible to prevent the occurrence of false color by lowering the level of the white clip signal SWC to lower the color dynamic range.

FIG. 9 shows an embodiment of the level conversion circuit 28. Here, 201 is an inverting amplifier, and 202 is a limiter. With this configuration, the characteristics shown in FIG. 8 are realized.

FIG. 10 shows an embodiment of the R process circuit 22. Here, 301 is a clamp circuit, 302 is a variable gain amplifier for performing white balance, 303 is a gamma correction circuit, 304 is a white clip circuit, and 305 is a blanking circuit.

The input signal resulting from the filtered output from the LPF 18 is first clamped by the clamp circuit 301, the gain of the variable gain amplifier 302 is varied according to the color temperature signal STC, and white balance is performed. After gamma correction by the gamma correction circuit 303 at the next stage, white clipping is performed by the white clipping circuit 304 with a voltage according to the white clipping signal SWC. Then, the blanking circuit 305 performs blanking and outputs the red signal SR1.

 The B process can be similarly configured.

In the above embodiment, the white clip level of the process circuit is varied by the output of the level conversion circuit. However, the Y signal is sliced by the level conversion output, and the chroma signal in the encoder is suppressed by the output. It may be configured as follows. With such a configuration,
Control can be performed with only one system.

Although the color temperature is detected by the color temperature detection circuit, it is detected by the gain control signal of R or B or both of the automatic white balance circuit that controls the average value of the color difference signals to be 0. May be.

Although the level conversion circuit 28 uses the detection method in which the output voltage decreases when the color temperature is lower than a certain color temperature, it is high when the color temperature is within a certain range near a certain center value, and when the color temperature is out of the range, the output voltage is high. It may be configured so as to decrease. Although the output voltage is configured to continuously decrease, it may be configured to change stepwise by switching between two stages or three or more stages. Also, if the level conversion circuit is a digital or analog function circuit and this input / output characteristic is configured to exactly match the relationship between the dynamic range of the color signal and the color temperature, it will always be possible to shoot with the widest dynamic range. Is possible.

The white clip level or the color suppression level may be set to be slightly larger than the dynamic range so that the false color level is suppressed in the vicinity of a level that is visually problematic.

Although the embodiment is applied to the single-plate television camera device using the solid-state image pickup device, the present invention can be similarly applied to other systems such as a single-tube, three-plate, three-tube system.

The present invention is configured in the case where the color dynamic range is limited by the image sensor, but the present invention is also applicable when other factors such as the dynmic range of the circuit limit and the limit changes depending on the color temperature. Can be applied.

〔The invention's effect〕

As described above in detail, according to the present invention, it is possible to realize an image pickup device having a wide dynamic range without causing false color in a high-luminance portion due to a change in color temperature.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing the relationship between the amount of incident light and the output of luminance and color signals in a single-tube type television camera, and FIG. 2 is a diagram showing the relationship between the amount of incident light, luminance and color signals in a television camera using a solid-state image sensor. FIG. 3 is a characteristic diagram showing the relationship with the output, FIG. 3 is a characteristic diagram showing the output characteristic after white balance is performed with the image sensor output based on the characteristic of FIG. 2, and FIG. 4 is an embodiment of the present invention. FIG. 5 is a block diagram showing the configuration of an image pickup device according to FIG. 5, FIG. 5 is a structural diagram for explaining the CCD shown in FIG. 4, and FIG. 6 is a waveform diagram showing timings for obtaining various signals from the output of the CCD. FIG. 8 is a characteristic diagram showing the relationship between CCD color output and color temperature, FIG. 8 is a diagram showing input / output characteristics of the level conversion circuit shown in FIG. 4, and FIG. 9 is a specific example of the level conversion circuit. FIG. 10 is a block diagram showing the configuration of the R process circuit shown in FIG. It is a block diagram showing a body example. 11 …… Imaging optical system 12 …… CCD 13 to 16 …… Sample and hold circuit 21 to 24 …… Process circuit 27 …… Color temperature detection circuit 28 …… Level conversion circuit SCC …… Imaging signal SY, SY1 …… Luminance signal SR, SG, SB, SR1, SG1, SB1 …… Color signal SDRY, SDBY …… Color difference signal STC …… Color temperature signal SWC …… White clip signal

Claims (1)

(57) [Claims] 1. An image pickup means, a variable gain amplifying means for changing the gains of a plurality of color signals formed by the image pickup means, a forming means for forming a signal according to a color temperature of a subject, and the formation. White balance adjusting means for adjusting the white balance by adjusting the gain of the variable gain amplifying means according to the output of the means, suppressing means for suppressing color signals of a predetermined level or more, and depending on the output of the forming means. , If the color temperature of the subject is higher than the first level V1,
Alternatively, when it is lower than the second level V2 (provided that V1> V2), an image pickup apparatus comprising: a control unit that controls the suppressing unit so as to suppress the color signal at a level lower than the predetermined level.