JP2513646B2 - Color imaging method - Google Patents

Description

The present invention relates to a so-called single tube or single plate color image pickup system for obtaining a color image signal by using one image pickup device.

(Prior Art) The conventional single-tube or single-plate color imaging method is roughly divided into a time division method and a plane division method.

The time-division system is a so-called CBS color system, which is a system in which a color filter of the same color for the entire screen is placed in front of one image sensor and the color of the filter is changed in field synchronization.

The surface division method is a method in which each color filter is arranged in a mosaic or stripe pattern on the front surface of one image sensor, and each color signal required for color image capturing can be surface-divided by the image sensor.

(Problems to be Solved by the Invention) In the time-division system, a still image can obtain a good color image equivalent to that of a so-called three-tube or three-plate system. However, in a moving image, when the color of the filter changes in synchronization with the field, the same subject does not exist in the same place. Therefore, it is not possible to obtain the subject for each color at the same time. When the image signal at this time is viewed as an image, a moving object appears to be colored in the order of color filters even in a monochrome (black and white) subject, resulting in a so-called color-split image.

For example, it is assumed that the color filter is composed of three primary colors of red, green and blue, and these are switched to the field child in this order. As shown in FIG. 3 (b), the image obtained when the state of the arrow in which the white ball 21 is moving as shown in FIG. 3 (a) is imaged is that the red, green, and blue color signals are This is a color breakup phenomenon that appears to be independent in size and area. Third
The ellipse of the ball in the figure (b) is due to the accumulation effect of the image sensor. The above-mentioned color breakup phenomenon is not preferable for a color television signal.

In the plane division method, there is no inconvenience regarding moving images as in the time division method described above. However, in this case, each color signal cannot be obtained for each picture element, but for each picture element. For example, such an example is a frequency-separated color imaging system
According to No. 8699), the equivalent arrangement of the color filters at this time is as shown in FIG. 4 (in the figure, W is white, Y is yellow, C is cyan, and G is green). When a white object is imaged by this method, the green signal is output for each filter, and red and blue are 1
It is output every other line. When 1 pixel is assigned to each color filter, the red signal and the blue signal are sampled every other pixel.

For this reason, in order to reduce the aliasing distortion, it is necessary to dispose an optical filter suitable for the sampling frequency, which suppresses the resolution. Further, in order to suppress the deterioration of resolution due to this filter, the pass band of the optical filter is widened, and when the light passes above the Nyquist frequency, the aliasing distortion increases. This occurs regardless of whether it is a still image or a moving image, and even in the plane division method, a good image equivalent to that of the three-tube or three-plate method cannot be obtained.

Therefore, an object of the present invention is to provide a color imaging system using a single imaging device, which eliminates the color breakup phenomenon in the time-division system moving image described above and eliminates the aliasing distortion and the resolution reduction problem in the plane-segmentation system. It is intended to be provided.

(Means for Solving the Problems) In order to achieve this object, the color imaging system of the present invention is
By periodically arranging each color filter in a mosaic or stripe pattern in front of one image sensor, and equivalently exchanging the geometrical positions of each color filter in time series, each color signal output can be output from the same position. Color image signals are obtained by obtaining them as a series, temporarily storing them in a storage device (frame or field memory), and then synthesizing them.

When synthesizing, it is determined whether the subject is a moving image or a still image. If it is a still image, the time-series information stored in the frame or field memory is used. If it is a moving image, the same frame or in-field information is used. A color image signal is obtained by using it.

With this method, for a still image, since information for each pixel is obtained for each color signal, a color image with the same resolution and color reproduction as the so-called three-tube type or three-plate type can be obtained. The requirement for the resolution is gradual due to the accumulation effect of the image and the deterioration of the resolution of the eye, and a sufficient image quality can be obtained by interpolating each sub-sampled color signal in the field.

The method of the present invention should be considered as a hybrid method that combines the time division method and the plane division method described in the section of the prior art.

(Example) The present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 (a) shows a basic configuration block diagram of an apparatus for achieving the system of the present invention. The image sensor 3 is a CDD,
Although various elements such as a MOS and an image pickup tube can be used, in the first embodiment shown in FIG. 1 (a), a CCD element is used as an image pickup element, and the scanning method is a line sequential method (30 frames / second). ).

The subject is a color filter 2 by the lens 1 of the imaging camera.
An image is formed on the pixel surface of the CCD image pickup device 3 via. The positional relationship between the pixels of the CCD image sensor 3 and the respective colors of the color filter 2 is shown in FIG. 1 (b). In this case, the respective colors of the color filter 2 are in the shape of a vertical stripe, and this color filter is
The color filter control circuit 10 shown in FIG. 1 (a) switches the color arrangement in synchronization with the frame. That is, as shown in FIG. 1B, in the first frame, R, G, B, ...
In the second frame, B, R, G, ..., In the third frame, G, B, R, ..., And these operations cycle every three frames. Therefore, when one pixel P shown in FIG. 1 (b) is taken in a column, color signals R, B, G are obtained in this order. This is exactly a "time division / plane division hybrid color signal" in which each color signal is subsampled both in time and space.

These color signals can form all pixels of one screen by synthesizing three frames. This state is shown in FIG. 1 (c). As for the signals of the R, G, and B color channels, the signals corresponding to all the pixels can be obtained in three frames indicated by numbers 1, 2, and 3 in the figure. This can be realized by writing information for all pixels in three frames in the frame memory corresponding to each color channel. The combination of these three frames is performed only for a still image, and since blurring occurs for a moving image, it is interpolated by the same intra-frame signal and not combined using three frames.

Regarding the interpolation, in the first embodiment, considering a certain channel shown in FIG. 1 (c), it suffices to perform the interpolation connecting between the same numbers, which can be realized by a low pass filter. Therefore, the signal output from the CCD element is determined by the motion detection circuit 6 whether it is a moving image or a still image. In the case of a moving image, frame interpolation is used, and in the case of a still image, it is combined using three frames. By doing so, the signal of each color signal can be obtained. It is the color signal separation circuit 7 that performs the above operation based on the determination of the motion detection circuit 6.

FIG. 1D shows an example of the color signal separation circuit 7. This is mainly composed of a frame memory, and FIG.
One color signal is shown in the figure, and three such circuit configurations are actually prepared. Considering one color signal, it is a signal in which the spatial positions that make one round in three frames are different, but in response to this, the frame memories 10, 11, 12 are set to the first, second,
It is allocated for the third frame, and the switches 13, 14, 15 are sequentially switched for each frame to write the video signal in the corresponding frame memory.

On the other hand, the circulated video signal is input to the motion detection circuit 6 and is compared with the video signal of three frames before, which is obtained by switching the switches 19, 20, 21 to detect the motion. According to the detected result, if the image is a still image, the switches 16, 17 and 18 are switched for each pixel to form one screen for one color of interest. In the case of a moving image, one frame is formed by using the frame memory in which the latest video signal is written among the frame memories 10, 11 and 12 and interpolating in the frame. The interpolation is performed by the low pass filter 8. The motion detection may be performed for only one color signal, but in this case, information on whether it is a still image or a moving image is supplied to the processing of each color signal.

When the signals color-separated by the color signal separation circuit 7 pass through the low-pass filter 8 as an interpolation filter, the cutoff frequency of the low-pass filter is naturally switched depending on whether it is a still image or a moving image. The signal output from the low-pass filter 8 is then subjected to final adjustment as a camera output signal by the process circuit 9, for example, γ correction, white clip, black clip, gain adjustment, etc., and then output.

By the above operation, each color signal is obtained for each pixel in the still image, and good color pixels are reproduced. Since the moving image is interpolated by the signal in the same frame, blurring due to this interpolation is not a concern.

The VTR5 shown in FIG. 1 (a) is added on the assumption that the signal after color filter processing is once recorded in the VTR5 and then reprocessed. The preprocessing circuit 4 is a preprocessing for recording. is there. Therefore, the VTR 5 and the preprocessing circuit 4 are not absolutely necessary in the structure of the present invention.

FIG. 2 is a diagram for explaining the second embodiment. The used color filters shown in FIG. 2 (a) are arranged in a mosaic pattern, and this array is known as a Bayer array. CCD is used as the image pickup device, and scanning is 2: 1 interlaced scanning. CCD for one of the color filters
2 pixels are allocated, and each pixel is alternately read in the odd field and the even field as shown. In the case of the present embodiment, each color signal output can be obtained from each pixel by adopting a method in which one cycle is performed every four fields. FIG. 2 (b) shows an example thereof and shows a color filter array from the first field to the fourth field. Based on the first field, the second
The field is vertically shifted by 2 pixels, or one color by color filter, the third field is horizontally shifted by one pixel, and the color filter is also shifted by one color, and the fourth field is vertically shifted by 2 pixels. The pixel is shifted. If they are shown by vectors, they will be as shown in FIG. 2 (c). The relative positional relationship in each field of the color filter is shown.

The output signal from the CCD having such a configuration is the first
In the same manner as in the above embodiment, the color signal is sent to the color signal separation circuit 7, color separation is performed according to a still image and a moving image, and a camera output signal is obtained via the interpolation filter 8 and the process amplifier 9. As a matter of course, in the case of a still image, it is obtained by synthesizing the signals of 4 fields because one cycle of 4 fields is performed.

Although two examples have been shown above, various combinations can be made depending on the arrangement of color filters, how to read out the CCD, and what is used for the image pickup device. However, in any of the methods, the present invention can be implemented by using an array of surface division type color filters and changing the array in synchronization with a frame or a field.

Any means may be used for changing the arrangement of the color filters, and the means is not limited, but there are a method of electrically changing the color of the color filters and a method of mechanically moving the color filters. As a method of mechanically changing the color filter, there are a method of mechanically changing the position of only the color filter and a method of moving the color filter and the image sensor at the same time as an integrated structure. Although the relative positional relationship between the pixel on the image sensor and each color of the color filter is different between the two, the two become equivalent by controlling the read timing of each pixel on the image sensor.

Further, the color filter has been described with the three primary colors of R, G, B, but the color filter is not limited to this, and a complementary color filter may be used.

Furthermore, in the explanation so far, in the color signal separation circuit,
Although different processing was performed for still images and moving images, the motion vector was detected for the moving image, the composite screen was shifted by the amount of the motion vector, the moving object image was fixed at the same place on the screen, and the cyclic field described above was used. It is also possible to synthesize and color-separate.

(Effects of the Invention) In a single-tube or single-plate color camera, by using the method of the present invention in which the plane division method using color filters and the time-division method are used in combination, a still image becomes a three-tube or three-plate color camera. The same color image quality can be obtained, and even in moving images, since there is blurring in the image sensor from the beginning, deterioration is less likely to be recognized than in the three-tube or three-plate system, and overall it is comparable to the three-tube or three-plate system. No image quality was obtained.

Unlike the multi-tube or multi-plate method, the single-tube or single-plate method does not require a color separation optical system, the camera itself can be downsized, and the camera lens can be easily designed, which contributes to the low cost of the camera.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (a), (b), (c) and (d) are views for explaining a first embodiment of the present invention, and FIGS. 2 (a) and (b). , (C) are diagrams for explaining the second embodiment of the present invention, FIGS. 3 (a), (b) are diagrams for explaining the color breakup phenomenon, and FIG. 4 is a surface division method of the conventional example. 1 of the array of color filters
It is a figure showing an example. 1 ... Camera lens, 2 ... Color filter 3 ... Imaging device (CCD), 4 ... Preprocessing circuit 5 ... VTR, 6 ... Motion detection circuit 7 ... Color signal separation circuit, 8 ... Low range Filter 9 …… Process circuit 10,11,12 …… Frame memory 13 to 18 …… Switch, 21 …… White ball

Claims (4)

(57) [Claims] 1. In a color image pickup camera using one image pickup device, the position of each color filter having a plurality of stripe-shaped or mosaic-shaped colors arranged periodically in front of the pixels of the image pickup device is set to a frame. Alternatively, a color image signal is obtained by circulating in synchronization with a field cycle, and combining the obtained output signals of the image pickup device between frames in a still image area or between fields, and interpolating in a frame or field in a moving image area. A color imaging method characterized by. 2. A color imaging system according to claim 1, wherein the plurality of colors are three primary colors. 3. A color imaging system according to claim 1, wherein the plurality of colors are complementary colors. 4. A color imaging system according to any one of claims 1 to 3, wherein the imaging device is a solid-state imaging device.