JP2001008096A - Video camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sharp video image even from highlight parts and dark parts in the video image by using a plurality of video signal correction characteristics in one frame in a video camera that is mainly connected to a computer or the like as its external device and used for a video conference or a video telephone or the like. SOLUTION: The video camera is provided with a video signal contrast distribution detection circuit 8 that checks a contrast distribution of a picture in order to change a plurality of video image correction characteristics in use depending on the contrast distribution of the picture and also with a block division circuit 9 that divides one frame into a plurality of blocks depending on the contrast distribution of the picture. The block division method of frame is configured through the provision of a means that changes sizes of the blocks depending on the contrast distribution of the picture.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to image correction of a video camera mainly used as a videophone, a video conference, etc., which is connected as an external device such as a computer.

[0002]

2. Description of the Related Art In recent years, a video camera has been connected to a computer for use as a video conference or video phone.
Use cases of video e-mail and the like in which a video from a video camera is recorded and compressed in a computer and the video is exchanged as an e-mail are increasing.

A video camera used in these applications processes an electric signal from an image pickup device that converts light from a CCD or the like into an electric signal into an appropriate video signal using a DSP or the like.
It is output as an analog or digital video signal. Then, when processing the electric signal from the image sensor into a video signal, various video signal correction processes are performed.
A typical example is a gamma correction process.

In the gamma correction processing, in a CRT displaying an image from a video camera, the brightness does not emit light in proportion to the magnitude of the signal input. Gamma correction process with the opposite characteristics to
The system up to T display is set in a proportional relationship to reproduce an image faithful to the subject.

In general, the characteristics of a CRT are expressed by X to the power of γ, where X is the input, and have a characteristic of γ = 2.2.
On the video camera side, γ = 0.4 to cancel this
Five characteristics are utilized.

In recent years, gamma correction has been performed not only to reproduce an image faithfully to a subject, but also to make the dark portion clearer by applying a correction such as assigning more gradations to a dark portion of the image. To achieve an image that looks good even at the expense of the fidelity of the image to the subject, such as obtaining an image or performing a correction that makes a sharp difference between dark and bright parts to obtain an image with a sense of contrast Sometimes used.

Conventionally, as a method of using such gamma correction, there is a proposal disclosed in Japanese Patent Application Laid-Open No. 6-70275. In Japanese Patent Application Laid-Open No. 6-70275, the gamma characteristic is changed according to the luminance distribution of a captured video signal.
This realizes a camera device capable of performing efficient bit assignment even when the luminance distribution is biased.

[0008]

However, Japanese Patent Laid-Open No. 6-7 / 1994
According to Japanese Patent No. 0275, for example, in a video having a bright portion and a dark portion in one frame, when a video signal correction is performed such that more tones are assigned to a dark portion of the video, the dark portion of the video has rich tones. Even if a good image is obtained, in a bright portion in the same frame, many gradations are assigned to a dark portion, so that usable gradations decrease, and sufficient gradation expression cannot be performed.

On the other hand, when a video signal is corrected so that more tones are assigned to bright parts, the number of tones that can be used for dark parts in the same frame decreases, and sufficient gradation cannot be expressed.

An object of the present invention is to solve the above problems, and is mainly connected as an external device such as a computer.
2. Description of the Related Art In a video camera used for videoconferencing, videophone, and the like, by correcting an image using a plurality of video signal correction characteristics in one frame, both bright and dark portions in the video are clear. It provides a beautiful image.

[0011]

SUMMARY OF THE INVENTION The video camera of the present invention has solved the above-mentioned problems, and the video camera of the present invention has a plurality of characteristics in an image in one frame when correcting a video signal. Video signal correction with
For this purpose, video imaging means for capturing an image of a subject and converting it into an electric signal, video signal processing means for processing the electric signal and converting it into a video signal, and video capable of correcting the video signal having a plurality of characteristics. There is provided a signal correction unit and a video signal output unit for outputting the video signal to an external device.

Further, a plurality of image correction characteristics to be used are changed depending on the brightness distribution of an image.
There is a light / dark distribution investigating means for examining the light / dark distribution of the image. The light and dark distribution of the image has means for using a frame before the frame being processed.

[0013] In addition, each of them performs appropriate image correction, and for that purpose, it has a block dividing means for dividing one frame into a plurality of blocks based on the brightness distribution of an image. Further, the method of dividing a frame into blocks has means for making the size constant regardless of the brightness distribution of the image.

Further, the method of dividing a frame into blocks has means for changing the size in accordance with the brightness distribution of an image. Further, there is provided means for reducing the amount of change in the correction characteristics between adjacent blocks to a predetermined value or less.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a video camera according to the present invention will be described with reference to FIGS.

FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, an image of a subject is focused on an image pickup device 2 through an image pickup lens 1. The image pickup device 2 converts the image condensed by the image pickup lens 1 into an analog electric signal as an electric signal of 30 frames per second by a signal from the image pickup device timing generation circuit 7. The signal converted into the analog electric signal is C
The signal is input to the DS / AGC / AD circuit 3 and is converted into a digital electric signal.

The signal converted into a digital electric signal is
The video signal is input to the video signal processing circuit 4 where color interpolation and various filter processes are performed to create a digital video signal separated into a luminance signal and a color signal.

The luminance signal among the video signals created here is input to the video signal light / dark distribution detection circuit 8. Here, an image in one frame is divided into a predetermined area of 2 × 2 or more in length and width, luminance in the area is integrated, an average value is calculated, and the information is divided into a block dividing circuit 9.
To enter.

The block dividing circuit 9 classifies each area according to a predetermined threshold value based on the integration result of each area.

The digital video signal generated by the video signal processing circuit 4 is subjected to signal correction by the video signal correction circuit 5 based on the signal from the block division circuit 9. The video signal correction circuit 5 performs correction having different characteristics for each block based on the block division information based on the luminance from the block division circuit 9.

The digital video signal corrected by the video signal correction circuit 5 is input to a video signal output circuit 6, converted into a signal suitable for input to a computer which is a receiving side of the video signal, and output. .

The CDS / AGC / AD circuit 3, image sensor timing generation circuit 7, video signal light / dark distribution detection circuit 8, and block division circuit 9 are controlled by a camera control microcomputer 10.

An embodiment in which an image is divided into 12 × 8 areas in one frame and further classified into three types of blocks according to luminance distribution will be described in detail with reference to FIGS.

FIG. 2 is an explanatory diagram showing a state where the image is divided into 12 × 8 areas in one frame. In the video signal light / dark distribution detecting circuit 8, the luminance of each area is divided into 96 areas. And calculate the average value. The luminance signal is expressed between 0 and 255, and the value increases as the luminance increases.

FIG. 3 is an explanatory diagram in the case of classifying into three types according to the luminance distribution.
According to the results shown in FIG.
If the number is 00 or more and less than 200, the data is classified with a number of "2", and if it is less than 100, the data is classified with a number of "1".

FIG. 4 is an explanatory diagram showing how an image in one frame is divided into three types of blocks according to luminance based on the results shown in FIG. As described above, the video signal correction circuit 5 performs correction having different characteristics in each block based on the block division information based on luminance.

In this embodiment, the number of area divisions is set to 96, but the accuracy of block division can be improved by increasing the number of divisions. In addition, when performing block division, the average value of the luminance of each area is calculated, but the same operation can be performed using the maximum value of the luminance in each area.

The digital video signal generated by the video signal processing circuit 4 is subjected to signal correction by the video signal correction circuit 5 based on the signal from the block division circuit 9.

The characteristic example of the correction performed here will be described in detail with reference to FIGS.

FIG. 5 is a characteristic diagram applied when the block division number in FIG. 4 is "1". The characteristic of this characteristic is that when the luminance input signal is around 100, the inclination of the correction straight line is 1 or more, and the gradation at low luminance can be expressed richer than when the inclination is 1. It is a characteristic.

FIG. 6 is a characteristic diagram applied when the block division number in FIG. 4 is "3". The characteristic of this characteristic is that the slope of the characteristic line is about 1 or more from about 200 to 255 for the luminance input signal, and the gradation at high luminance can be expressed richly.

FIG. 7 is a characteristic diagram applied when the block division number in FIG. 4 is "2". The characteristic of this characteristic is that, when the luminance input signal is about 120 to 180, the gradation expression is slightly deteriorated, but when the luminance input signal is seen from about 80 to 220, the slope of the characteristic line becomes 1 It has close characteristics.

The characteristics shown in FIG.
And the characteristic near the boundary surface are set to be close to continuous. This is because when the characteristics shown in FIGS. 5, 6, and 7 are used, the continuity of luminance may be lost around the boundary surface of the block division depending on the image data, but the effect is reduced.

This break in the continuity of gradation can be reduced by increasing the number of area divisions to improve the accuracy of block division or by increasing the types of block division. Further, in the present embodiment, the characteristic of the gamma correction is represented by γ =
Although treated as 1, the gamma characteristic can be corrected by adding the gamma characteristic to the characteristics shown in FIGS. 5, 6, and 7 when the gamma characteristic is other than 1.

In the actual video signal correction processing, the characteristics shown in FIGS. 5, 6, and 7 are applied to one frame image according to the block division number, and both the low luminance portion and the high luminance portion are corrected. As before, rich gradation expression is possible, and a moderate gradation expression is also possible in the middle luminance portion.

In this embodiment, the correction is performed only on the luminance signal. However, it is also possible to correct the color signal in the same manner. The correction characteristics determined here are applied to the image of the next frame.

This is because, when the characteristics are detected and corrected in the same frame, the correction most suitable for the image can be performed. For this purpose, at least one frame of the image is stored. Memory becomes necessary, which causes a complicated camera system and an increase in cost.

On the other hand, if the characteristics are applied to the image of the next frame, only the classification after the block division needs to be stored, which is advantageous in cost.

[0039]

Since the video camera apparatus of the present invention has the above-described configuration, it is possible to provide a better image to the user as compared with the case where only a single correction characteristic is implemented. In addition, it is possible to provide a user with an image rich in gradation. The light and dark distribution of the image can provide the user with an image with rich gradation, and can provide a video camera that is advantageous in cost without using an image memory or the like.

Further, it is possible to provide an image having a natural gradation feeling. Furthermore, when only a single correction characteristic is implemented, it is possible to simplify the correction circuit while providing an image with a sense of gradation in comparison. Furthermore, correction suitable for the image can be performed, and it is possible to provide a more natural image with a sense of gradation and a sense of contrast. Further, after the image is corrected, it is possible to minimize the loss of continuity such as luminance.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a state where an image is divided into 12 × 8 areas in one frame.

FIG. 3 is an explanatory diagram in the case of classifying into three types according to a luminance distribution.

FIG. 4 is an explanatory diagram showing how an image in one frame is divided into three types of blocks according to luminance.

FIG. 5 is a characteristic diagram applied when a block division number is “1”.

FIG. 6 is a characteristic diagram applied when a block division number is “3”.

FIG. 7 is a characteristic diagram applied when a block division number is “2”.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 imaging lens 2 video imaging device 3 CDS / AGC / AD circuit 4 video signal processing circuit 5 video signal correction circuit 6 video signal output circuit 7 imaging device timing generation circuit 8 video signal light / dark distribution detection circuit 9 block division circuit 10 camera control Microcomputer

Claims (7)

[Claims] 1. An image pickup means for picking up an image of a subject and converting it into an electric signal, a video signal processing means for processing the electric signal and converting it into a video signal, and capable of correcting a video signal having a plurality of characteristics. Video signal correction means, and a video signal output means for outputting the video signal to an external device, wherein a video signal having a plurality of characteristics is corrected for an image in one frame. . 2. The video camera according to claim 1, further comprising a light / dark distribution examining means for examining the light / dark distribution of the image, wherein a plurality of image correction characteristics to be used are changed according to the light / dark distribution of the image. 3. The image light distribution according to claim 2, wherein a frame prior to the frame being processed is used.
The described video camera. 4. The image processing apparatus according to claim 2, further comprising: a block dividing unit that divides one frame into a plurality of blocks according to a brightness distribution of an image, and performs an appropriate video correction for each block.
The described video camera. 5. The video camera according to claim 4, wherein the block division has a fixed size regardless of the brightness distribution of the image. 6. The video camera according to claim 4, wherein the size of the block division is changed according to the light and dark distribution of the image. 7. The method according to claim 4, wherein the amount of change in the correction characteristic between adjacent blocks is equal to or less than a predetermined value.
The described video camera.