JPH04351085A - Conditional picture element supplement system - Google Patents

Abstract

PURPOSE:To improve the quality of a transmission picture by comparing a transformation coefficient at a prescribed frequency area with plural reference values and deciding a threshold level depending on the level. CONSTITUTION:A transformation coefficient being an output of an orthogonal transformation section 300 is inputted to a threshold level control section 450 provided to a picture element supplement section 400 and the control section 450 compares the transformation coefficient at a prescribed frequency area with a preset 1st reference level. When the transformation coefficient larger than the 1st reference level is in existence, the threshold level is set to a 2nd reference level. When all the transformation coefficients for the prescribed area are smaller than the 1st reference level, the control section 450 sets the threshold level to a 3rd reference level larger than the 2nd threshold level. In this case, the orthogonal transformation section 300 obtains a difference of the picture data between frames for each block and applies orthogonal transformation to the difference data and outputs a transformation coefficient represented by a frequency component. Then the threshold level is set to a larger value to set forcibly the transformation coefficient to zero and outputted, then the quality of the transmission picture is improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conditional pixel supplementation method in an image encoding device using orthogonal transformation.

At this time, there is a need for a conditional pixel supplementation method that improves the quality of transmitted images.

0003

2. Description of the Related Art FIG. 3 is a block diagram showing the configuration of an example of an interframe encoding device. FIG. 4 is a diagram showing an example block configuration.

FIG. 5 is a diagram showing an example of a zigzag scan. FIG. 6 is a diagram illustrating an example of a quantization step. FIG. 7 is a flowchart for explaining the operation of the conventional example.

In FIG. 3, data obtained by digitizing analog image information using an analog/digital converter (not shown) is input to a blocking section 1, and is divided into a predetermined number of blocks for each frame. In this case, it is assumed that each block is composed of 4×4 pixels in the vertical direction and the horizontal direction, respectively, as shown in FIG. 4, for example. Add the data of this block to one input terminal of the subtraction unit 2, add the image data at the same block position one frame before, stored in the frame memory 8, to the other input terminal, and subtract the two input data in the subtraction unit 2. The difference between the two is calculated and the output is sent to the orthogonal transform unit 3.
Add to.

The orthogonal transform unit 3 performs orthogonal transform using discrete cosine transform (DCT) on each pixel of a block consisting of 4×4 pixels in the vertical and horizontal directions as shown in FIG. Converts pixel data into frequency component data and outputs conversion coefficients. These transform coefficients are added to the conditional pixel replenishment section 4, and the conditional pixel replenishment section 4 performs a zigzag scan as shown in FIG. 5 for each transform coefficient of the block. Let Ci be the conversion coefficient after the zigzag scan.

As shown in FIG. 7, each conversion coefficient Ci
(In this case, i = 0 to 15), the absolute value ABS (Ci) is compared with a preset threshold Th, and there is at least one ABS (Ci) that exceeds the threshold Th in one block. When doing so (see ■ in FIG. 7, sigb=1), each conversion coefficient Ci is output as is (see ■ in FIG. 7). or,
Absolute value ABS of all transform coefficients Ci in one block
When (Ci) is less than or equal to the threshold value Th, the values of all conversion coefficients Ci are set to 0 and output as shown in (■) in FIG.

The output of the conditional pixel replenishment section 4 is applied to a quantization section 5, and the quantization section 5 performs predetermined quantization. The output of the quantization unit 5 is sent to a subsequent circuit (not shown) and is also added to the inverse orthogonal transformation unit 6. Perform the conversion. Then, the adder 7 adds the image data of the same block one frame before read from the frame memory 8,
The output of the inverse orthogonal transform unit 6 is added to the difference data, and the added output is written and stored in the frame memory 8 again. Further, as described above, the image data of the same block read out from the frame memory 8 one frame before is added to the subtraction unit 2, and the subtraction unit 2 calculates the difference between it and the input data added from the blocking unit 1. The data output is applied to the orthogonal transform section 3.

[0009]

[Problems to be Solved by the Invention] However, in the conventional system, the conditional pixel replenishing unit 4
If there is a transform coefficient Ci whose ABS(Ci) exceeds the threshold Th at any time, each transform coefficient Ci is output as is, and all transform coefficients C in one block are
When the absolute value ABS(Ci) of i is less than or equal to the threshold value Th, the values of all conversion coefficients Ci are forcibly set to 0 and output.

Therefore, if a conversion coefficient Ci exceeding the threshold value Th appears only in high frequencies due to noise, etc., it is not possible to forcefully set the value of all conversion coefficients Ci to 0 and output it, and waste information is lost. There is a problem in that the transmission path cannot be used effectively and the quality of the transmitted image deteriorates.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a conditional pixel replenishment scheme that improves the quality of transmitted images.

0012

Means for Solving the Problems The above problems are solved by the circuit configuration shown in FIG. That is, in Figure 1, 1
Input image data for each frame, divide it into a fixed number of blocks, find the difference between the image data of the previous frame and the corresponding block, perform orthogonal transformation on the difference data, and output transformation coefficients represented by frequency components. Orthogonal transform unit 300
) and the output transform coefficients of the orthogonal transform unit 300 are input, and when the absolute values of all the transform coefficients in the block are smaller than the threshold value, all the transform coefficients in the block are set to 0 and output. 450 is provided in the pixel filling unit 400 and compares the transform coefficients in a predetermined frequency domain with a first reference value,
The threshold value is set to a second reference value when there is a conversion coefficient larger than the reference value of This is a threshold value control unit that sets a third reference value that is larger than the second reference value.

[0013]

[Operation] In FIG. 1, the transform coefficients of the output of the orthogonal transform section 300 are input to the threshold control section 450 provided in the pixel replenishment section 400, and the threshold setting section 450 inputs the transform coefficients of the output of the orthogonal transform section 300 to the threshold control section 450 provided in the pixel supplement section 400. ) and a preset first reference value (for example, a quantization step). Then, when a conversion coefficient larger than the first reference value exists, the threshold value is set to the second reference value. Further, when all the transform coefficients in a predetermined frequency domain are smaller than the first reference value, the threshold value is set to a third reference value that is larger than the second reference value.

[0014] When there are transform coefficients larger than the threshold thus set, all transform coefficients in the block are output as they are. Further, when the absolute values of all the transform coefficients in the block are smaller than the threshold value, all the transform coefficients in the block are set to 0 and output.

As a result, even if there is a transform coefficient that exceeds the threshold only in the high frequency region within the block due to noise etc., the threshold is set to a large value (third reference value), so the "block" All conversion coefficients < threshold (
3rd reference value)", and all conversion coefficient values can be forced to 0 and output. Therefore, the transmission path can be used effectively and the quality of the transmitted image can be improved. .

[0016]

Embodiment FIG. 2 is a flow chart for explaining the operation of an embodiment of the present invention. The same reference numerals indicate the same objects throughout the figures.

The difference between the present invention and the conventional example is that the threshold value is controlled depending on whether or not there is a significant coefficient exceeding the threshold among the transform coefficients on the low frequency side within the block, and When a significant coefficient exists, it is assumed that there is information to be sent, and the threshold value is set to a slightly larger value. Also, when there is no significant coefficient in the conversion coefficient on the low frequency side, it is assumed that there is no information to be sent, and the threshold value is set to a larger value to actively set the value of the conversion coefficient to 0. There is a particular thing.

[0018] This will be explained in more detail below. In FIG. 3, the functions of circuits other than the conditional pixel replenishment unit 4, that is, the blocking unit 1, the subtraction unit 2, the orthogonal transformation unit 3, the quantization unit 5, the inverse orthogonal transformation unit 6, the addition unit 7, and the frame memory 8 Since it is the same as that explained in the related art, the explanation thereof will be omitted.

The transform coefficients output from the orthogonal transform section 3 shown in FIG. Perform a zigzag scan as shown. Let Ci be the conversion coefficient after the zigzag scan. Then, for example, it is determined whether or not the transformation coefficients (in this case, Co, C1, C2) are significant coefficients for the low frequency region of the block shown with diagonal lines in FIG. 4 (see ■ and ■ in the flowchart in FIG. ). In this case, the minimum unit g of the quantization step shown in FIG. 6 is used as the determination criterion.

[0020] Then, one of Co, C1, and C2
Even if the absolute value is greater than g (see ■ in Figure 2)
, it is assumed that there is a significant coefficient and that there is information to be sent, and the threshold Th is set to Th=1.4 g (see ■ in FIG. 2). Furthermore, when the absolute value of any of the conversion coefficients Co, C1, C2 on the low frequency side is smaller than g, it is assumed that there is no significant coefficient and there is no information to be sent, and the threshold value Th is
is set to a larger value Th = 2.0 g (see ■ in FIG. 2).

Using the value of the threshold value Th set in this way, the transformation coefficient Ci (i=0 to 15) within the block is calculated.
Determine the value of That is, the absolute value ABS(
Ci) is compared with the threshold Th (see ■ in Figure 2), and when the absolute value ABS (Ci) of all conversion coefficients Ci (i = 0 to 15) in the block is smaller than Th, the Set all Ci to 0 (see ■ in Figure 2).

[0022] Also, all the transform coefficients Ci(
i=0~15), its absolute value ABS(Ci
) is larger than Th (see ■ in Figure 2), the values of all transform coefficients Ci in the block are output as they are (
(See ■ in Figure 2).

As mentioned above, the above series of operations is performed by the conditional pixel replenishing unit 4, but the circuit in this case can be made of hardware such as a comparison circuit (not shown) and a logic circuit (not shown). However, it can also be created by software using, for example, a microcomputer.

The conversion coefficient Ci (i=
0 to 15) are added to the quantization unit 5 shown in FIG. 3, and the quantization unit 5 performs predetermined quantization. Since the other circuits are the same as those described in the prior art, their description will be omitted.

As a result, even if there is a transform coefficient Ci that exceeds the threshold Th only in the high frequency region within the block due to noise etc., Th is set to a large value, so Ci (i = 0 to 15) <Th, and the values of all conversion coefficients Ci can be forced to 0 and output. Therefore, it is possible to improve the quality of transmitted images.

[0026]

As described above, according to the present invention, it is possible to improve the quality of transmitted images.

[Brief explanation of the drawing]

FIG. 1 is a diagram of the principle of the present invention.

FIG. 2 is a flowchart for explaining the operation of the embodiment of the present invention;

FIG. 3 is a block diagram showing the configuration of an example interframe encoding device;

FIG. 4 is a diagram showing an example block configuration;

FIG. 5 is a diagram showing an example of a zigzag scan,

FIG. 6 is a diagram showing an example of a quantization step;

FIG. 7 is a flowchart for explaining the operation of the conventional example.

[Explanation of symbols]

450 indicates a threshold control section.

Claims (1)

[Claims] Claim 1: Input image data for each frame, divide it into a fixed number of blocks, find the difference between the image data of the previous frame and the corresponding block, and perform orthogonal transformation on the difference data to convert it into frequency components. an orthogonal transform unit (300) that outputs the represented transform coefficient;
), and when the absolute values of all the transform coefficients in the block are smaller than the threshold value, a pixel replenishment unit (400) that outputs the output transform coefficients by setting all the transform coefficients in the block to 0; A coding device having a predetermined frequency domain transform coefficient and a first reference value,
When there is a conversion coefficient larger than the reference value, the threshold is set to a second reference value, and when all the conversion coefficients in the predetermined frequency region are smaller than the first reference value, the threshold is set to The pixel replenishment unit (400) includes a threshold control unit (450) that sets the value to a third reference value that is larger than the second reference value.
A conditional pixel replenishment method characterized by providing.