JP2000270333A - Image signal coder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coder in which a still picture from the coder does not cause a picture different from each GOP. SOLUTION: This coder has a coding section 11, a buffer 12 that stores 1 frames, a discrimination section 13 that discriminates a still/moving area from a preceding I frame stored in the buffer 12 and a current I frame in the unit of macro blocks, a buffer 14 that stores a bit stream in the unit of macro blocks outputted from the coding section in the case of I frames, a buffer 15 that stores a code quantity produced in the unit of macro blocks in the case of I frames, a calculation discrimination section 16 for a generated code quantity in the case of replacing a macro block discriminated to be a still area with a code of a preceding I frame in the case of I frames, and a bit stream generating section 17 for I frames from a header of the I frames outputted from the buffer 14 and a bit stream in the unit of macro blocks. Thus, the macro blocks discriminated to be a still area replaced with a bit stream of a preceding I frame.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image encoding apparatus using MPEG, and provides an encoding apparatus in which a still portion such as a background does not become an image different for each GOP.

[0002]

2. Description of the Related Art FIG. 2 shows an example of an image encoding sequence using MPEG. Here, several frames are composed of units called GOPs, one of which is subjected to intra-frame encoding called an I-frame, and the other frames are P-frames for performing forward prediction and B-frames for performing bidirectional prediction. Each frame is encoded. Each frame is divided into units called macroblocks. In the case of a P frame or a B frame, a motion vector is detected for each macroblock, a coding mode is determined, and a quantization value is determined. The prediction error, the motion vector, and the encoding mode are encoded. In the case of an I frame, a quantization value is determined for each macroblock, and coding is performed.

[0003] For a stationary part, in a P frame, a motion vector is set to zero and no prediction error is coded.
By selecting oded, in the decoded image, the image at the same position of the previous I frame is copied and output. In the B frame, the motion vector is set to zero,
By not sending the prediction error, it is possible to reproduce the same image as the previous I frame from the similarly decoded image. As described above, it is possible to encode all the frames in the GOP so as to obtain the same decoded image as that of the I frame for the stationary portion.

However, the next I frame is coded independently of the previous I frame. For this reason, regarding the stationary portion, the quantized value may be different due to code amount control, or the decoded image may be different even if the quantized value is the same due to noise or the like in the image. . In such a case, since the still portion becomes a different image for each GOP, the change becomes visually conspicuous in GOP units, causing visual deterioration.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has been made so that a still portion does not become a different image for each GOP. The same decoded image can be generated between GOPs with respect to a still portion so as not to cause the same.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to an image signal encoding apparatus which performs encoding using MPEG, an encoding unit which performs MPEG encoding on an input image. 11, in the case of an I frame, a frame buffer 12 for storing the input image, and a determination of performing a still / moving area determination on a macroblock basis from the previous I frame and the current I frame stored in the frame buffer. A bit stream buffer 14 for storing a macroblock unit bit stream output from the MPEG encoding unit in the case of an I frame, and a code for storing a code amount generated in a macroblock unit in the case of an I frame. Amount buffer 15 and, in the case of an I frame, the macroblock determined as a still area by the determination unit
A code amount determination unit 16 for calculating a generated code amount when replacing with a frame code; and a bit for forming an I frame bit stream from an I frame header and a macro block unit bit stream output from the bit stream buffer. It has a stream generation unit 17, and in the case of an I-frame, for a macroblock determined to be a still area, if the virtual buffer value does not underflow, it is replaced with a bitstream of the macroblock of the previous I-frame. As an image signal encoding device,
Regarding the still part, the same decoded image can be generated between GOPs.

(Operation) According to the present invention, in encoding of an image using MPEG, a still / moving area is determined for each I-frame of an adjacent GOP in macroblock units. By outputting the bit stream of the macro block of the I frame instead of the bit stream of the macro block of the current I frame, the visual quality of the still area is improved.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of an encoding apparatus according to the present invention will be described below with reference to FIG. The encoding apparatus according to the present invention shown in FIG. 1 includes an MPEG encoding unit 11, an I frame buffer 12, a code amount determination unit 13, a bit stream buffer 14, a code amount buffer 15, and a code amount determination unit 1.
6 and a bit stream forming unit 17.

[0009] The input image is supplied to an MPEG encoding unit 11 and subjected to general MPEG encoding (encoding of MPEG1, MPEG2 and MPEG4). If the input image is an I frame, the input image is also stored in the I frame buffer 12. The input image is encoded by the MPEG encoding unit 11, and P
In the case of a frame and a B frame, the generated bit stream is output to the bit stream forming unit 17.

When the input image is an I frame, a bit stream in units of macro blocks is output to the bit stream buffer 14, and the code amount in units of macro blocks is
Output to the code amount buffer 15. For I-frames,
Both the previous I frame already stored in the I frame buffer 12 and the I frame to be processed are supplied to the still area determination unit 13.

The static region determination unit 13 compares two I frames in macroblock units for each macroblock, and determines whether the region is a still or moving region.
The result of the determination is supplied to the code amount determination unit 16. The code amount determination unit 16 reads the code amount of each macroblock of the previous I frame and the code amount of each macroblock of the current I frame from the code amount buffer 15.

[0012] The code amount of the previous I frame is represented by the code amount (Im (n-
1)), the code amount of the macroblock in the still area (Is (n-
1)), so the total code amount is Ih + Im (n-1) + Is
(n -1). The code amount of the I frame currently being processed is calculated from the head part (Ih), the code amount of the macroblock in the moving area part (Im (n)), and the code amount of the macroblock in the still area part (Is (n)). Therefore, the total code amount is Ih + Im
(n) + Is (n).

Here, when it is determined that the area is a still area, the total code amount of the I frame when it is replaced with the code of the macroblock of the previous I frame is Ih + Im (n) + Is (n-1). This value is input to the virtual buffer (VBV (Video Buffe
If the value is smaller than the value of the ring verifier (buffer), the code can be replaced, so this determination is made.

The code amount determination unit 16 controls the bit stream buffer 14 to control whether the code of the current I frame or the code of the macro block of the previous I frame is output for each macroblock. Do it. VB
If the V-buffer causes an underflow, the code of the current I frame is output for all macroblocks.

If the VBV buffer does not cause underflow, the code of the previous I frame is output for the macroblock determined as the still area, and the macroblock determined as the moving area is output for the macroblock determined as the still area. , To output the code of the current I frame.

For the macroblock determined to be a still area, the code amount buffer unit 15
The generated code amount of the macroblock of the I frame is overwritten with the generated code amount of the current macroblock of the I frame.

Similarly, the bit stream buffer unit 14
, The bit stream of the macroblock of the previous I frame is overwritten with the bit stream of the macroblock of the current I frame. Similarly, the image data of the macroblock of the previous I frame is read out from the I frame buffer
The image data of the macroblock of the current I frame in the frame buffer is overwritten. In addition, the code amount determination unit 16 outputs the total code amount of the I frame to be output to the MPEG encoding unit 11 so as to be used for the code amount control of the next frame.

The bit stream forming unit 17 outputs the bit stream from the MPEG encoding unit 11 as it is for a P frame and a B frame, and outputs a header input from the bit stream buffer 14 for an I frame. A bit stream of an I frame is formed from the bit stream in units of macroblocks and output.

As described above, the function of outputting the code of the preceding I frame stored without performing the coding of the macroblock determined as the still area in the input image is provided. , The same decoded image can be generated between GOPs, thereby eliminating the change in the image caused by the difference between the decoded image of the I frame and the still area such as the background, thereby improving the visual image quality. .

[0020]

According to the present invention, the change of the image caused by the difference between the decoded image of the I frame and the still area such as the background can be eliminated, and the visual image quality can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of an encoding device of the present invention.

FIG. 2 is a diagram showing a sequence of image encoding using MPEG.

[Explanation of symbols]

 Reference Signs List 11 MPEG encoding section 12 I frame buffer 13 Still area determination section 14 Bit stream buffer 15 Code amount buffer 16 Code amount determination section 17 Bit stream formation section

Claims (1)

[Claims] 1. An image signal encoding apparatus for encoding using MPEG, comprising: an encoding unit for performing MPEG encoding on an input image; and in the case of an I frame, a frame buffer for storing the input image. A determination unit for determining a still / moving region in macroblock units based on a previous I frame and a current I frame stored in the frame buffer; and in the case of an I frame, a macro output from the MPEG encoding unit. A bit stream buffer for accumulating a bit stream in block units; a code amount buffer for accumulating a code amount generated in macro block units in the case of an I frame; A code amount determining unit for calculating a generated code amount when a block is replaced with a code of a previous I frame; A bit stream generator for forming an I-frame bit stream from an I-frame header and a macro-block-based bit stream output from a buffer, and in the case of an I-frame, a virtual buffer for a macro block determined to be a still area. An image signal encoding apparatus characterized in that when a value does not underflow, it is replaced with a bit stream of a macroblock of a previous I frame.