JPH07250332A - Saturated output expanding method for four-plate solid-state image pickup device - Google Patents

Abstract

PURPOSE:To expand a saturated output of the 4-plate solid-state image pickup device while keeping a proportional relation between a level of an object image of each color and a corresponding image pickup element output level. CONSTITUTION:An object image is formed by an objective lens 30, the image is decomposed into red, green and blue images by a color separation prism 31 and the green image is decomposed into two images by a half mirror 31a. The decomposed green lights are made incident respectively on a CCD 32G-1 and a CCD 32G-2 respectively and picture signals obtained from the CCD 32G-1 and the CCD 32G-2 are composited by an adder 36. Since the luminous quantity of the green light is divided into two and the luminous quantity of the red image is reduced by a neutral density(ND) filter 37, the incident luminous quantity to the CCD 32R, the CCD 32G-1, the CCD 32G-2 and the CCD 32B is almost made coincident to increase each incident luminous quantity to the vicinity of a saturating point of the incident luminous quantity of the CCD, then the saturated output is expanded more than that of a conventional solid-state image pickup device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device, and more particularly to a subject image is decomposed into three primary color images of red, green and blue, which are respectively received by a solid-state image pickup device to extract red, green and blue signals. The present invention relates to a saturation output expansion method for a four-plate solid-state imaging device.

[0002]

2. Description of the Related Art Recently, in order to improve the resolution of a solid-state image pickup device, two image pickup elements are arranged in a green (G) channel,
A four-plate type solid-state image pickup device has been proposed in which a spatial image shift is performed between these two image pickup elements. Such a four-plate solid-state image pickup device is disclosed, for example, in Japanese Patent Laid-Open No. 60-154781, Japanese Patent Laid-Open No. 5-129513 and NHK Broadcasting Technology Research Institute 1993.
It is described in the annual technical report.

[0003]

However, although the resolution is improved in the conventional 4-plate type solid-state image pickup device, the saturation output, that is, the dynamic range with respect to the amount of light incident on the lens, which is one of the important properties of the solid-state image pickup device, is limited. There is a drawback. The reason why the saturation output is limited in the four-plate type solid-state imaging device will be described below.

When the image pickup device converts the imaged light into an electric signal and outputs the electric signal, the level of the electric signal is proportional to the amount of light input to the image pickup device. That is, weak light is converted into a low level signal, and strong light is converted into a high level signal. However, such a proportional relationship does not always hold, and when a certain amount of light is incident,
The level of the electric signal is not proportional to the amount of incident light and is a constant level. FIG. 1 shows the relationship between the amount of light incident on the solid-state image sensor and the level of the output signal of the solid-state image sensor. The region where the output signal level is proportional to the incident light amount is called the linear region, and the region where the output signal level does not increase above a certain value even when the incident light amount increases is called the saturation region. The saturated incident light amount that changes is determined at the time of manufacture from the structure of each image sensor and the like.

FIG. 2 is a schematic configuration diagram of a conventional three-plate type solid-state image pickup device. In such a three-plate solid-state image pickup device, an image of a subject is formed by the objective lens 10, this is separated into red, green, and blue images by the three-color separation prism 11, and these color images are respectively CCDs 12R, 12G, and 12B. To image. At this time, under a light source with a color temperature of around 3000 ° K, which is usually used in studios, etc., C
The amount of light incident on the CDs 12R, 12G and 12B is 3
Due to the characteristics of the color separation prism 11, the red light and the green light have almost the same amount, and the blue light has almost 1/1 / the red light or the green light.
It will be 3-1 / 4. When shooting a subject image with this solid-state imaging device, when the light amount of the subject is increased, the CC
D12R and 12G saturate, then CCD 12B saturates. In this way, when the saturation timing is different between the CCDs, one of the CCDs (in this case, the CCD 12R
And 12G) after saturation, when the amount of light is further increased, CC corresponding to the amount of light of the subject image of each color is obtained.
The proportional relationship with the output level of D is broken, and the color reproducibility is deteriorated. For example, when a white subject image is taken and the amount of light is increased, either CCD (in this case, CC
If the amount of light is further increased after saturation of D12R and 12G), a white subject image will be colored and reproduced.

In order to prevent such coloring, in the conventional device shown in FIG. 2, white clip circuits 13R, 13G and 13B are provided for CCDs 12R, 12G and 12B.
Are provided respectively. White clip circuit 13
R, 13G, and 13B correspond to other CCDs (in this case, in accordance with the maximum value of the output of the first saturated CCD (in this case, CCD 12R and 12G) of the imager outputs of the respective colors in the signal processing system of the solid-state imager. Is to limit the maximum output level of the CCD 12B) to the same level. Further, the clipping points of the white clipping circuits 13R, 13G and 13B are usually adjustable, and these clipping points are taken by the CCD 1 after the white subject is imaged and the incident light amount is increased.
It is set to the saturation point of the CCD (CCD 12R and 12G in this case) which reaches the saturation point first among 2R, 12G and 12B. Therefore, in the case of the three-plate type solid-state imaging device, the saturation amount is limited by the CCD 12R, 12G and 12B having the highest incident light amount ratio.

White clip circuits 13R, 13G and 13B in which the red, green and blue signals obtained from the CCDs 12R, 12G and 12B are set to the saturation points of the red and green signals respectively, and the signal processing circuit 14
It is supplied to the luminance matrix circuit 15 through R, 14G and 14B, and mixed at a predetermined ratio to generate a luminance signal.

FIG. 3 is a schematic configuration diagram of a conventional four-plate type solid-state image pickup device. In this four-plate type solid-state image pickup device, a subject image is formed by an objective lens 20, and the four-spectrum prism 21 divides it into red, green, and blue images, and further, a green image is divided into two images by a half mirror 21a. It is the one. Further, the light receiving elements of the CCDs 22G-1 and 22G-2 are arranged so as to receive the divided green light by being shifted from each other in the horizontal scanning direction by almost half of the arrangement interval. After the decomposed green lights are respectively incident on the CCDs 22G-1 and 22G-2, the image signals obtained thereby are combined by the adder 26. Therefore, the sensitivity of the green signal is not impaired.

In such a four-plate type solid-state image pickup device, since the green light is equally divided into two, CCDs 22G-1 and 22G are used.
The amount of light incident on each -2 is 1/2 that of the CCD 12G of the three-plate solid-state imaging device of FIG. At this time, since the saturation amount of one CCD does not change, the saturation amount of each CCD that receives green light is twice as large as that of the three-plate solid-state imaging device. However, the amount of red light is the same as that of the three-plate solid-state image pickup device even though the same amount of light as that of the green light is incident, and thus the saturation amount of such a four-plate solid-state image pickup device is limited by the red light. As it is, it is no different from the three-plate type solid-state imaging device. That is, even if the 3-plate type is changed to the 4-plate type, the saturation amount as the solid-state imaging device does not change, and there is a drawback in that the effect of the 4-plate type cannot be obtained.

An object of the present invention is to expand the saturation output of a four-plate type solid-state image pickup device capable of expanding the saturation output without breaking the proportional relationship between the light amount level of each color subject image and the corresponding output level of the image pickup device. It provides a method.

[0011]

According to the method for expanding saturation output of a four-plate type solid-state image pickup device according to the present invention, when expanding the saturation output of a four-plate type solid-state image pickup device, a subject image is red-colored via a color separation optical system. It is decomposed into three primary color images of green and blue, and the green image is further divided into two to obtain four images, and the two divided green images are shifted from each other in the horizontal scanning direction by about half of the arrangement interval of the light receiving elements. The first and second solid-state imaging devices arranged in this way receive light, the third solid-state imaging device receives a blue image, and the fourth solid-state imaging device receives a red image with a reduced amount of light, From the fourth solid-state image sensor, the green signal obtained by combining the first and second image signals from the first and second solid-state image sensors, the blue signal obtained from the third solid-state image sensor, and the fourth solid-state image sensor. The obtained red signal and the brightness Synthesized by the trix is characterized in creating a luminance signal.

[0012]

In the saturation output expansion method of the four-plate solid-state image pickup device according to the present invention, the subject image is separated into the images of the three primary colors of red, green and blue by the color separation optical system, and the green image is further divided into two and divided into four. Two images. The two-divided green image is received by the first and second solid-state imaging devices in which the light-receiving elements are displaced from each other in the horizontal scanning direction by almost half of the arrangement interval, and the blue image is received by the third solid-state imaging device. The red image is received by the fourth solid-state image sensor, and the light amount of the red image is, for example, a neutral density filter or a filter for reducing the amount of red transmitted light on the surface of the color separation optical system that outputs the red image. Decrease by placing.

Here, even if an ideal filter that reduces only the amount of red light is inserted in front of or immediately after the lens forming the subject image, the same effect as that of the present invention should be obtained. It is difficult to obtain an optical filter that reduces the amount of light in the red wavelength range. When the filter is arranged in front of or immediately after the lens, channels of other colors are also affected, and it is difficult to obtain the same effect as that of the present invention.

Color temperature 300 usually used in studios
Under a light source of around 0K, the amount of light of each color decomposed by the color separation optical system is almost the same for red light and green light due to the nature of the color separation optical system, and blue light is 1 / red of red light or green light. It becomes 3 to 1/4, but since the amount of green light is divided into two, it becomes 1/2 of that when it is not divided into two, and since the amount of red light is further reduced, each color incident on the solid-state image sensor is reduced. The ratio of the light amount of is closer to the same ratio as in the case of the conventional three-plate type or four-plate type solid-state imaging device. For example,
If the ratio of the amount of light incident on the solid-state image sensor of the conventional 3-plate red, green, and blue channels is 1: 1: 1/3,
In the plate type, the amount of light incident on the green solid-state image sensor is halved, but the amount of light incident on the red solid-state image sensor does not change, so the amount of light incident on the red, green, and blue channel solid-state image sensors does not change. The ratio is 2: 1: 2/3, and in the present invention, the amount of light incident on the green solid-state image sensor is 1/2, and the amount of light incident on the red solid-state image sensor is 1 / n by the neutral density filter.
If it is reduced to 2, the light intensity ratio becomes 1: 1: 2/3,
The ratio approaches 1.

As described above, the saturation output of the solid-state image pickup device is limited by the solid-state image pickup device having the highest incident light amount ratio. The saturation output of the imager is expanded. Therefore, the incident light quantity of each solid-state image pickup element can be increased to near the saturation amount without breaking the proportional relationship between the light quantity level of the subject image and the corresponding output level of the image pickup element. The saturation output can be expanded as compared with the solid-state image pickup device.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A saturation output expansion method for a four-plate solid-state image pickup device according to the present invention will be described with reference to the drawings. FIG. 4 is a schematic configuration diagram of a four-plate type solid-state imaging device using the saturation output expansion method according to the present invention. This four-plate type solid-state imaging device is
ND (Neutral Density) filter 3 for plate type solid-state imaging device
7 is inserted between the color separation prism 31 and the CCD 32R. The color separation prism 31 separates the subject image formed by the objective lens 30 into red, green and blue images, and further separates the green image into two green images by the half mirror 31a. The decomposed green image enters the CCDs 32G-1 and 32G-2, which are arranged so that the light receiving elements are displaced from each other in the horizontal scanning direction by about half of the arrangement interval and receive the divided green light,
The image signals obtained from the CCDs 32G-1 and 32G-2 are combined by the adder 36. Therefore, the sensitivity of the green signal is not impaired. The ND filter 37
Insertion of the red channel, that is, the optical path length of the CCD 32R does not deviate from the optical path lengths of other channels.
Adjustments have been made for this.

In such a four-plate type solid-state image pickup device, green light is divided into two equal parts, and therefore CCDs 32G-1 and 32G-
The amount of light incident on each of the two is half that of the CCD 12G of the three-plate type solid-state imaging device shown in FIG. At this time, since the saturation amount of one CCD does not change, the saturation amount of green light is twice as large as that of the three-plate type solid-state imaging device. On the other hand, the red light enters the CCD 32R after the light amount is reduced by the ND filter 37. That is, the amount of red light received by the CCD 32R decreases.

The amount of light of each color separated by the color separation prism 31 is substantially the same for red light and green light due to the property of the color separation prism, and blue light is 1/3 to 1/4 of red light or green light. However, since the amount of green light is divided into two, the amount of light is 1/2 of that when not divided, and the amount of transmitted red light is reduced by the ND filter 37.
The ratio of the amount of light of each color incident on the CCD 32R, CCD 32G-1, CCD 32G-2, and CCD 32B is closer to the same ratio as in the case of the conventional 3-plate or 4-plate solid-state imaging device. That is, when a white image is taken, the CCDs 32R, 32 corresponding to the amount of light incident on the objective lens 30.
The linear regions in which the G-1, 32G-2, and 32B solid-state imaging devices operate are approaching. Therefore, the level of the subject image and the CCD 32R, CCD 32 corresponding to this level
G32, CCD32G-2, CCD32B, CCD32R
CD32G-1, CCD32G-2 and CCD32B
The amount of light incident on each can be increased to near the saturation point, and the saturation output can be expanded as compared with the conventional solid-state imaging device using the same CCD.

In the four-plate solid-state image pickup device of the present invention shown in FIG. 4, the amount of red light incident on the CCD 32R is reduced by the ND filter 37, but the absolute saturation amount of the CCD 32R does not change. Therefore, the saturation point of red light is N
It rises as compared with the case where the D filter 37 is not inserted. The rate of increase depends on the light transmittance of the ND filter 37.
In the four-plate solid-state imaging device of FIG. 1, if the light transmittance of the ND filter 37 is set so that the saturated output of the CCD 32R and the saturated output of the CCD32G-1 and CCD32G-2 are the same, the four-plate solid-state imaging device. The saturation output of the entire device can be expanded.

When the saturation output is to be expanded in the three-plate type solid-state image pickup device or the conventional four-plate type solid-state image pickup device without reducing the transmitted light amount of red light as in the above-mentioned embodiment, R, G and B There is a method to increase the amplification rate of all signal processing systems and reduce the amount of light incident on each image sensor with respect to the amount of light incident on the color separation optical system.
In this case, since the amplification factor is increased in all the R, G, and B channels, the noise component of the image pickup device is increased by the increase in the amplification factor, which is inconvenient.

In this example, the color separation prism 31 and CC
By inserting the ND filter 37 between it and D32R, the sensitivity of the R channel is lowered and the signal output of the CCD 32R is reduced. Therefore, in order to maintain the balance of R, G, and B, it is necessary to increase the amplification factor of the signal processing system of the R channel, and the S / N of the R channel decreases. On the other hand, the S / N of the solid-state imaging device is determined by the brightness signal. In the case of HDTV signals, the ratio of R, G, B signals in the luminance signal is

## EQU00001 ## Y = 0.2125R + 0.7154G + 0.0721B, and the R channel accounts for only 20% of the whole, and the S / N reduction of the R channel does not significantly affect the S / N reduction of the entire solid-state imaging device.

In this example, by making the ND filter 37 detachable, the S / N ratio of the R channel at low illuminance is reduced.
The ratio can be increased. In this case, the ND filter 37
ND filter 37 so that the gain of the R channel is lowered in conjunction with the removal of the optical path and the optical path length does not change.
A plate with the same refractive index as is inserted instead.

The present invention is not limited to the above-mentioned embodiments, but various modifications and changes can be made. In the above-described embodiment, ND is used to reduce the transmittance of red light.
Although a filter is used, a glass material having a low red light transmittance may be used instead, or a dichroic film having a different red light reflectance may be provided on the color separation prism.

[0024]

As described above, according to the saturation output expansion method of the four-plate solid-state image pickup device according to the present invention, the proportional relationship between the level of the subject image and the corresponding output level of the image pickup device is maintained and the solid-state image pickup device of each solid-state image pickup device is maintained. Since the incident light amount can be increased to near the saturation amount, the maximum allowable incident light amount as a solid-state image pickup device can be increased. Therefore, a conventional three-plate type or four-plate type solid-state image pickup device using the same solid-state image pickup device can be used. The saturated output can be expanded in comparison.

[Brief description of drawings]

FIG. 1 is a relationship diagram between the amount of light incident on a solid-state image sensor and the signal output of the solid-state image sensor.

FIG. 2 is a schematic configuration diagram of a conventional three-plate solid-state imaging device.

FIG. 3 is a schematic configuration diagram of a conventional four-plate solid-state imaging device.

FIG. 4 is a schematic configuration diagram of a four-plate solid-state imaging device using the saturation output expansion method according to the present invention.

[Explanation of symbols]

 30 Objective Lens 31 Color Separation Prism 31a Half Mirror 32R, 32G-1, 32G-2, 32B CCD 33R, 33G, 33B White Clip Circuit 34R, 34G, 34B Signal Processing Circuit 35 Luminance Matrix Circuit 36 Adder 37 ND Filter

Claims (2)

[Claims] 1. When expanding the saturation output of a four-plate type solid-state imaging device, a subject image is separated into three colors of red, green and blue via a color separation optical system.
A first image in which the green image is decomposed into primary color images and the green image is further divided into four images into four images, and the two divided green images are arranged such that the light receiving elements are offset from each other in the horizontal scanning direction by about half of the arrangement interval.
And the second solid-state imaging device receives the light, the third solid-state imaging device receives the blue image, and the fourth solid-state imaging device receives the red image with a reduced amount of light. A green signal obtained by combining the first and second image signals from the solid-state image sensor;
A saturated output of a four-plate solid-state image pickup device, characterized in that a blue signal obtained from the solid-state image pickup device of 1) and a red signal obtained from the fourth solid-state image pickup device are combined in a luminance matrix to create a luminance signal. Expansion method. 2. The method according to claim 1, wherein a neutral density filter or a filter that reduces the amount of transmitted red light is disposed on the surface of the color separation optical system that outputs a red image to reduce the amount of red light. A method for expanding saturation output of a four-plate solid-state imaging device, comprising: