JPH0222981A - Picture signal processing method - Google Patents

Abstract

PURPOSE:To eliminate visual incongruity due to the steep change of the luminance of a display picture by outputting each image element signal as data for code processing after applying luminance adjustment to add a luminance correction value at a preceding frame on each image element signal of the present frame. CONSTITUTION:A pre-processing part in a television conference system is constituted of a television camera 10, an A/D converter 11, a Y/C separator 12, a luminance average operation circuit 13, a luminance correction circuit 14, a luminance correction value calculation circuit 15, a memory 16, and a frame memory 17. Here, the image element signal at every frame is outputted as the data for code processing after the luminance correction of the present frame image element is performed by a correction value based on the arithmetic mean of the luminance correction value of the preceding frame stored in advance and the average luminance of all image elements of the present frame. Therefore, no remarkable difference among continuous frames is generated. In such a way, it is possible to solve the incongruity on a picture due to the steep change of the luminance of an image picked up picture.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image signal processing method, particularly an image signal processing method that improves preprocessing technology for encoding and transmitting image data in a video conference system, system, etc. Regarding.

[Prior Art] Videophone/videoconferencing systems that integrate various signals such as moving images, audio, still images, etc. using telephone lines and enable higher-level communication of intentions or information are being put into practical use. In particular, the latter method does not require a dedicated conference room, and simply requires a space-saving, compact device installed in the office, allowing people in multiple different locations, both near and far, to communicate their intentions simultaneously through images and audio. It has attracted attention for its ability to improve communication, and there is a growing momentum to introduce it within companies as a means of reducing business trips for meetings.

A video conference system is a combination of a video camera and a CRT monitor, which converts the analog image signal (image data taken from the camera) into digital data, encodes it, and sends it to the other party's system via a telephone line. .

Since the amount of communication information required when transmitting television images over a communication line increases rapidly, encoding processing aims to reduce transmission costs and time by compressing this into a smaller amount of information.

In this way, each person's image captured by the other party's camera is CR
In the case of an internal conference, the video captured by the other party's camera will be displayed as is on the CRT monitor, and in the case of an external conference, the video will be compressed using an image compression device. Become. If necessary, video display switching between the user's side and the other party's side can be performed by pressing a button.

[Problem 8 to be Solved by the Invention] However, in conventional video conferencing systems, the television camera may be moved to change the target image during imaging. At this time, if the brightness in the room differs significantly between the imaging location before the move and the imaging location after the move, due to factors such as lighting and the presence or absence of windows, there is a problem that this will appear as is on the display screen. Ta.

For example, as shown in Figure 2 (A), if a television camera (1) installed indoors is photographing a person in a meeting with a window (2) in the background, Because it is not directly exposed to external light, the brightness of the image is relatively low. If the camera (1) is moved from this state to the position indicated by the dotted line in the figure, the brightness of the image will rise rapidly because the light from the window (2) will be directed straight toward the object to be imaged.

As a result, as shown in FIG. 2(B), a sudden change in brightness occurs on the display screen of the CRT monitor due to the movement of the camera.

As a result, the brightness on the screen may vary depending on the person, which may give the viewer a sense of discomfort.

Additionally, the display screen, which previously had a constant brightness, suddenly becomes darker or brighter due to the movement of the camera, which can significantly reduce visibility and prevent the meeting from continuing smoothly. .

Purpose of the Invention The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to provide an image signal processing method that can effectively eliminate the discomfort on the screen caused by sudden changes in brightness of a captured image. be.

[Means for Solving the Problem] In order to achieve the above object, the present invention calculates the average brightness of the pixel signal for each frame before outputting the pixel signal captured by a television camera as data for encoding processing. a step of calculating, a step of storing the same, a step of calculating a brightness correction value of the pixel signal for each frame, and a step of correcting each pixel signal so that its average brightness matches the brightness correction value, and then encoding it. This method performs signal processing consisting of a step of outputting as processing data.

The brightness correction value is calculated by an arithmetic average of the average brightness of the current frame and the brightness correction value of the previous frame.

[Operation] According to the method of the present invention configured as described above, the pixel signal for each frame is corrected based on the arithmetic average of the brightness correction value of the previous frame stored in advance and the average brightness of all pixels of the current frame. After the brightness of the current frame pixel is corrected based on the value, it is output as data for encoding processing.

Therefore, since the average brightness of each frame is always corrected to be the intermediate value between the output average brightness of the previous frame and then output as data for encoding processing, the brightness of each successive frame will not differ greatly from each other. There isn't.

[Example] Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

FIG. 1 shows an example of the configuration of a preprocessing section of a video conference system to which the method of the present invention is applied. Image data of a person is captured as an analog pixel signal Sa by television cameras (10) arranged at a plurality of locations, and is digitally converted by an A/D converter (11). The output signal Sd of the A/D converter (11) includes a luminance component (Y) and a color component (C),
Although each is subjected to separate processing, color component processing will be omitted here.

Luminance signal Sy extracted by Y/C separator (12)
is a brightness correction circuit (14) and a brightness average calculation circuit (13).
), and the brightness average calculation circuit (13) calculates the average brightness 5I11 of the pixels for each frame.

The average brightness signal Sa+ from the brightness average calculation circuit (13) is supplied to the brightness correction value calculation circuit (15).

A memory (16) is connected to the correction data calculation circuit (15), and a brightness correction value 5M-1 of the frame immediately before the current frame is stored in the memory (16). The correction data calculation circuit (15) calculates the average luminance S of the current frame.
m and previous frame luminance correction value 5M-1 in memory (16)
The correction data SM of the current frame is calculated by taking the arithmetic mean of the data, and is outputted to the brightness correction circuit (14).

In the brightness correction circuit (14), the Y/C separator (12)
The luminance signal Sy of each pixel transmitted from the luminance correction circuit (
The brightness level is corrected based on the brightness correction value SM for the current frame from 15), and the data SY for encoding processing is
is sent to the frame memory (17) as -
once written according to a predetermined address. Thereafter, the stored data for encoding processing is sequentially outputted for encoding transmission processing in accordance with a clock signal from a frame read counter (not shown), starting from the oldest data.

The specific effects will be explained in detail below.

First, a plurality of pixel signals corresponding to the first frame are processed as described above (A/D converter (11) and Y/C separator (11)
2) and then undergoes processing for calculating the average brightness within the brightness average calculation circuit (13). The average luminance signal Sm is
It is supplied to the correction data calculation circuit (15). Regarding this first frame, since there is no previous frame, correction data is calculated as follows. That is, the average luminance Sml of the first frame is stored in the correction data calculation circuit (15).
An upper threshold Thmu and a lower threshold Thmd are set in advance for Sml if Thmd≦Sml≦Thmu
, leave Sml as is, that is, Sml
= Output as SM.

The average luminance of the first frame itself is used as correction data.

On the other hand, if Sml is not between the upper and lower thresholds, that is, if the brightness of the first frame is extremely high or low,
The upper threshold value Thmu or Thmd itself is regarded as the correction data SMI.

This first brightness correction value SMI is stored in the memory (16).
The brightness correction circuit (14) outputs the brightness correction circuit (14). At the same time, the brightness signal Sy of each pixel is sequentially input from the Y/C separator (12) to the brightness correction circuit (14), and this brightness signal Sy is the brightness as it is when captured by the television camera (10). It is. Each signal undergoes brightness correction in the brightness correction circuit (14) based on the brightness correction value SMI from the correction data calculation circuit (15), and then is stored at the corresponding address in the frame memory (17) as data SY for encoding processing. It will be written in.

This correction is performed for the purpose of matching the encoding processing data SY, that is, the average brightness of each pixel signal after correction, to the brightness correction value SM.

Next, the pixel signals for the second frame similarly pass through the A/D converter (11) and the Y/C #i unit (12), and the average brightness S+2 of all pixels is calculated in the brightness average calculation circuit (13). After being calculated, it is supplied to a brightness correction value calculation circuit (15). At this time, the brightness correction value calculation circuit (15) is connected to the memory (16).
The brightness correction value SMl for the first frame stored in the memory is read out, the arithmetic mean of the brightness correction value and the average brightness Sm2 of the second frame is calculated, and the calculation result is used to correct the second frame. It is supplied to the brightness correction circuit (14) as brightness data SM2. Then, as mentioned above, the brightness correction circuit (14) applies brightness correction to the pixel signals Sy2 sequentially transmitted from the Y/C separator (12) by adding this correction data SM2, and then directs them to the frame memory (17). and output as encoding processing data SY2.

Thereafter, each subsequent frame is subjected to brightness correction based on the arithmetic average of its average brightness Sm and the brightness correction data 5M-1 for the previous frame stored in the memory (16). The data will be sequentially written into the frame memory (17) as data for naturalization processing SY. SY represents the brightness of the pixel signal after correction.

Therefore, it is understood that as a result, the average value of SY for one frame becomes equal to SM.

With the above configuration, even if there is a large change in brightness due to the movement of the TV camera during imaging, the brightness correction described above is performed before encoding processing, and the brightness of each frame is always based on the brightness of the previous frame. It won't be far apart.

As a result, the brightness on the CRT monitor changes in a very natural manner without giving the viewer a sense of discomfort.

[Effects of the Invention] As explained above, according to the method of the present invention, after the brightness adjustment is performed by adding the brightness correction value of the previous frame to each pixel signal of all frames, the data is processed as code processing data. Since the display image is outputted, the visual discomfort caused by sudden changes in the brightness of the displayed image can be reliably eliminated.

[Brief explanation of the drawing]

FIG. 1 is an example of the configuration of a video conference system to which the image signal processing method according to the present invention is applied, and FIG. 2 is an explanatory diagram of the prior art. In the figure, (10) is a TV camera, (11) is an A/
D converter, (12) 4; tY/C separator, (13) is a brightness average calculation circuit, (14) is a brightness correction circuit, (15) is a brightness correction value calculation circuit, (16) is a memory, (17) ) is frame memory. In the drawings, the same reference numerals indicate the same or corresponding parts. Agent Patent attorney Masuo Oiwa (2 others) Explanatory diagram of the prior art, Figure 2 (A) Illustration of the prior art, Figure 2 (B) Procedural amendment 1 (voluntarily) Date of invention: 2 Name of Image Signal Processing Method 3, Relationship with the Person Who Makes the Amendment Patent Applicant Address 2-2-3 Marunouchi, Chiyoda-ku, Tokyo Name (601) Mitsubishi Electric Corporation Representative Moriya Shiki 4, Agent Person Address: 2-2-3 Marunouchi, Chiyoda-ku, Tokyo 5° Drawings subject to correction

Claims (1)

[Scope of Claims] An image signal processing method for outputting pixel signals as data for encoding processing, comprising the steps of: calculating the average brightness of the pixel signals for each frame; storing the calculated average value; The process includes a step of calculating a brightness correction value of a pixel signal for each frame, and a step of outputting as data for encoding processing after correcting the average brightness of the pixel signal of each frame to be equal to the brightness correction value. . An image signal processing method, wherein the previous luminance correction value is an arithmetic average value of the average luminance of the current frame and the luminance correction value of the previous frame.