JPH04189092A - Orthogonal transformation coding device and decoding device - Google Patents

Abstract

PURPOSE:To properly make the distribution of non-zero coefficients after an orthogonal transformation by increasing the scan motion in that direction only, if the scan order is distributed in the vertical and horizontal directions in accordance with the generation distribution of the non-zero coefficients. CONSTITUTION:The picture signals entered into a picture input terminal 1 are orthogonally transformed for every block by an orthogonal transforming unit 2. One of the transformation coefficients, which are the output of the transforming unit 2, is a DC coefficient which shows the average value of the block and the others are AC coefficients indicating the variation manner and both of them are inputted to a quantizer 3. The quantizer 3 quatizes each coefficient at a preset skip width, outputs the results to a scan section 4 and reads into a block memory 5. At this time, the scan order is in line with the generation distribution of the non-zero coefficients and if the distribution is in the direction of vertical/horizontal, the scan movement in the direction of vertical/ horizontal direction only is set to be increased by a scan preset means. Thus, no mismatch occurs between the distribution after the orthogonal transformation and scan groups.

Description

Detailed Description of the Invention (Industrial Application Field) A high-efficiency encoding method that digitizes an image signal with a smaller amount of code in a device that records, transmits, and displays an image signal. The present invention relates to a transform encoding device and a decoding device.

(Prior Art) In high-efficiency encoding using orthogonal transform such as DCT (discrete cosine transform), many of the transformed signals (coefficients) can be regarded as zero.

Therefore, if there are many coefficients determined to be 0,
It is more efficient to encode them all at once than to encode them individually.

As a specific method, 2
There is a method in which the dimensional coefficients are rearranged into one dimension and the 0 coefficients are encoded as consecutive numbers.

FIG. 4 is a diagram showing the conventional scan order.

In FIG. 4, arrows represent scan types and points represent converted components (coefficients).

There are eight coefficients both horizontally and vertically, and each coefficient is defined as kIT.

Here, X is the number from the lowest frequency in the horizontal direction, and y is the number from the lowest frequency in the vertical direction.

Therefore, kH is a DC component, and k77 is a component with the highest frequency.

The scan type is the one with lower frequency both vertically and horizontally (k 0
0) to the higher one (k77), the two-dimensional coefficients are rearranged into a one-dimensional array by zigzag scanning.

All parts except the end portions are scanned in a 45-degree diagonal direction, with one horizontal movement and one vertical movement performed at the same time.

One-dimensional coefficients are looked at in order from the beginning, and when a non-zero coefficient occurs, it is calculated as the number of zero coefficients between that coefficient value and the previous non-zero coefficient value (or start). The two types of values are each encoded using a variable length code such as a Huffman code.

Here, the number of 0 coefficients is called 0 run length, and it goes without saying that it is necessary to encode even when there are consecutive non-zero coefficients and zero 0 coefficients.

The shorter the 0-run length is, the smaller the average code number can be.

Therefore, when non-zero coefficients are generated in a concentrated manner in one dimension, the amount of code for the 0-run length is smaller than when they are generated dispersedly.

Therefore, it is sufficient to scan in order of low frequency components with a high probability of non-O occurrence.

(Problems to be Solved by the Invention) The scanning method shown in the conventional example is suitable for a non-interlaced signal in which the sample interval is close to a square.

However, a typical television signal is an interlaced signal in which one frame is divided into two fields.

FIG. 5 is a diagram showing sampling points when an interlaced signal is sampled field by field. The broken line indicates the shape of an 8×8 pixel block.
゛'In Figure 5, the vertical sample interval is approximately twice the horizontal sample interval, and if DCT is performed on such a signal using 8x8 pixels as in the past, the vertical force direction Many non-zero coefficients occur.

FIG. 6 is a diagram showing the distribution of non-zero coefficients after orthogonal transformation between a non-interlaced signal and an interlaced signal. In the figure, dense indicates a portion where the distribution density of non-zero coefficients is high, and coarse indicates a portion where the distribution density of non-zero coefficients is low.

For the non-interlaced signal in FIG. 6(A),
It can be seen that the interlaced signal in Figure (B) spreads approximately twice as much in the vertical direction.

Therefore, there is a mismatch between the scans shown in FIG. 4 and the distribution of non-O coefficients in FIG. 6(B), resulting in an unnecessarily large amount of generated codes.

The present invention has been made with attention to the above points, and when scanning two-dimensional orthogonal transform coefficients to make them one-dimensional and run-length encoding coefficients that become 0, the scan order is changed according to the occurrence of non-O coefficients. Depending on the distribution, if the distribution is wide in the vertical direction, increase the movement of the vertical scan, and if the distribution is wide in the horizontal direction, set the movement of only the horizontal scan to be large. Therefore, there is no mismatch between the distribution of non-zero coefficients after orthogonal transformation and the scanning types, and the scanning is adapted to the distribution of non-zero coefficients, the average value of the 0-run length is lowered, and the amount of code generated is small. The object of the present invention is to provide an image encoding device and a decoding device.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides the following steps: (1) When scanning two-dimensional orthogonal transform coefficients to make them one-dimensional and run-length encoding coefficients that become 0, Adjust the scan order to match the occurrence distribution of non-O coefficients, and if the distribution spreads in the vertical direction, increase the number of scans in the vertical direction, and if the distribution spreads in the horizontal direction, increase the number of scans in the horizontal direction only. Provided is an orthogonal transform encoding device characterized by having a scan order setting means for setting a large number of scan movements, and (2) when inversely scanning the scanned and one-dimensional coefficients into a two-dimensional array, Adjust the order to match the occurrence distribution of non-O coefficients, and if the distribution spreads in the vertical direction, increase the number of scans in the vertical direction, and if the distribution spreads in the horizontal direction, scan only in the horizontal direction. The present invention provides an orthogonal transform decoding device characterized by having scan order setting means for setting a large number of movements.

(Operation) As a method of setting the scan Jung class, when the occurrence distribution of non-O coefficients spreads in the vertical direction, the high frequency components in the vertical direction are scanned earlier than the high frequency components in the horizontal direction.

Specifically, about half of the parts that were previously all diagonal movements are now moved in the vertical direction.

Since the scan Jung class has a shape that approximately matches the frequency of occurrence of non-zero coefficients, the length of the 0-run length becomes shorter and the amount of code becomes smaller.

(Embodiment) FIG. 1 is a block diagram showing an orthogonal transform encoding device of the present invention.

In FIG. 1, an image signal input from an image input terminal 1 is supplied to an orthogonal transformer 2.

The orthogonal transformer 2 orthogonally transforms the input signal for each 8×8 pixel block using a method such as DCT (discrete cosine transform).

Among the transform coefficients output from the orthogonal transformer 2, one is a DC coefficient that indicates the average value of the block, and the others are AC coefficients that indicate the state of change.
Each coefficient is supplied to the quantizer 3.

The quantizer 3 quantizes each coefficient with a set step width, supplies the output (mostly 0) to the scan unit 4, and writes it into the block memory 5.

The scanning unit 4 includes a block memory 5. Changeover switch 6, ROM7. It is composed of a counter 8.

The address of the block memory 5 is when writing (W),
It can be changed at readout time.

During writing, the changeover switch 6 is connected to the W side.

The output signal of the counter 8 is supplied to the ROM 7 and the ROM
This address is used as the address of the block memory 5, and is also supplied as the write address of the block memory 5 via the changeover switch 6.

During reading, the changeover switch 6 is connected to the R side.

The ROM 7 is a ROM in which the scan order of the present invention as described later is written, and is supplied as a read address of the block memory 5 via the changeover switch 6.

The block memory 5 actually consists of two sides of memory,
While one is writing, the other is for reading.

The output signal of the block memory 5 converted into the scan order is supplied to a run-length encoder 9.

The run-length encoder 9 receives non-zero coefficient values of the input signal,
The 0-run length value is variable-length coded and output to a decoding device or the like via a data output terminal 10.

FIG. 2 is a block diagram showing an orthogonal transform decoding device of the present invention. The decoding device performs the reverse processing of the encoding device.

In FIG. 2, an encoded data signal from an encoding device or the like is input from a data input terminal 1 and is supplied to a run-length decoder 12.

The run length decoder 12 performs variable length decoding on the non-zero coefficient values and 0 run length values of the input signal,
3 and writes it into the block memory 5.

The scanning unit 13 includes a block memory 5. Changeover switch 6, ROM7. It is composed of a counter 8.

The address of the block memory 5 is when writing (W),
It can be changed at readout time.

During writing, the changeover switch 6 is connected to the W side.

The ROM 7 is a ROM in which the scan order of the present invention as described later is written, and is supplied as a write address of the block memory 5 via the changeover switch 6.

As a result, the output signal of the run-length decoder 12 is
The data is returned to the original arrangement and written to the block memory 5.

During reading, the changeover switch 6 is connected to the R side.

The output signal of the counter 8 is supplied to the ROM 7 and the ROM
This address is used as the address of the block memory 5, and is also supplied as the read address of the block memory 5 via the changeover switch 6.

The block memory 5 actually consists of two sides of memory,
While one is writing, the other is for reading.

The output signal of the block memory 5 which has been returned to its original arrangement is supplied to an inverse quantizer 14.

The inverse quantizer 4 inversely quantizes the input signal and supplies it to the inverse orthogonal transformer 15.

The inverse orthogonal transformer 15 performs inverse DCT transform on the input signal, obtains a reproduced image signal, and outputs it via an image output terminal 6.

A feature of the present invention is the setting of scan types, and this scan order setting means will be explained below.

As described above, this scan order setting means is stored and set in the ROM 7 of the encoding device shown in FIG. 1 and the ROM 7 of the decoding device shown in FIG. 2.

FIG. 3 is a diagram showing the scan order of the present invention.

In Figure 3, four types of scan orders (A) to (D) are shown, in which two-dimensional coefficients are 1 Sort into an array of dimensions.

In the conventional scan type shown in FIG. 4, except for the end portions, one movement in the horizontal direction and one movement in the vertical direction are performed at the same time, and scanning is performed in a diagonal direction of 45 degrees.

In contrast, in the present invention, about half of the scan is performed only in the vertical direction.

Since there are 8 coefficients in the vertical direction, it moves 7 times, but 3 to 4 of them are moved only in the vertical direction.

Let each coefficient be kxy. Here, X is the number from the lowest frequency in the horizontal direction, and y is the number from the lowest frequency in the vertical direction.

Therefore, koo is a DC component and k77 is a component with the highest frequency.

FIG. 3(A) shows k x2 from kxl. The three types of movement from k13 to kx4 and from kx5 to kx5 are made only in the vertical direction, from kxQ to kxl, and from kx2 to k! 3.
The four types of movement from kx4 to kx5° and from kx6 to kxl are the same as in the conventional case.

This will create a discontinuous part at the end, but it will be connected to the nearest one, as shown by the broken line in the figure.

This makes scanning approximately twice as fast in the vertical direction as compared to the conventional example.

Figure 3 (B) shows kxQ to kxl, kx3 to kx
The three types of movement from 4°kx6 to kxl are made only in the vertical direction, and there are fewer discontinuous parts than in FIG. 3(A).

Figure 3 (C) shows kxl from kxo, kx3 from kx2.
, kx4 to kx5. The four types of movement from kx6 to kxl are performed only in the vertical direction, and scanning is faster in the vertical direction than in FIGS. 3(A) and 3(B).

Note that there are two types of scans depending on which direction to start from.

These are in an inverse relationship to each other, and the other type was traced by regarding k77 as 00.

Figure 3 (B) shows the horizontal and vertical lowest frequencies other than DC (
In other words, in the figure, when 01 and 10) are not consecutive and there are only non-zero coefficients (kol and k10), if kol and klO are separated by scan type, there will be a long O-run length between them, which will be disadvantageous. In that case, Figure 3 (D)
By changing only the start as shown in , it becomes equivalent to the others.

In the above explanation, the case where the distribution of non-zero coefficients spreads in the vertical direction was described, but the same applies to the case where the distribution of non-zero coefficients spreads in the horizontal direction. Of course it's a good thing.

(Effects of the Invention) The image encoding device and decoding device of the present invention scan two-dimensional orthogonal transform coefficients to make them one-dimensional, and when performing run-length encoding of coefficients that become 0, the image encoding device and decoding device of the present invention change the skikin order to non-zero coefficients. According to the occurrence distribution, if the distribution is spreading in the vertical direction, increase the scan movement only in the vertical direction, and if the distribution is spreading in the horizontal direction, set the movement of the scan only in the horizontal direction. Therefore, there is no mismatch between the distribution of non-zero coefficients after orthogonal transformation and the scanning order, and the scanning is adapted to the distribution of non-zero coefficients, reducing the average value of 0-run lengths and reducing the amount of code generated. It has extremely excellent practical effects, such as reducing the number of tasks.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the orthogonal transform encoding device of the present invention, FIG. 2 is a block diagram showing the orthogonal transform decoding device of the present invention, FIG. 3 is a diagram showing the scan order of the present invention, and FIG. is a diagram showing the conventional scan order, Figure 5 is a diagram showing the state of sampling points when an interlaced signal is sampled field by field, and Figure 6 is a diagram showing non-zero coefficients after orthogonal transformation between a non-interlaced signal and an interlaced signal. FIG. 2 is a diagram showing the distribution of DESCRIPTION OF SYMBOLS 1... Image input terminal, 2... Orthogonal transformer, 3... Quantizer, 4.13... Scan section, 5... Block memory, 6... Changeover switch, 7... ROM,
8...Counter, 9...Run length encoder, 1
0...Data output terminal, 11...Data input terminal,
12... Run length decoder, 14... Inverse quantizer, 15... Inverse orthogonal transformer, 16... Image output terminal 3, Patent applicant: Victor Japan Co., Ltd. Figure 1 Figure 2 Figure 4Figure 3

Claims (2)

[Claims] (1) Scan the two-dimensional orthogonal transformation coefficients to make them one-dimensional,
When run-length encoding coefficients that become 0, the scan order is adjusted to match the occurrence distribution of non-zero coefficients, and if the distribution spreads in the vertical direction, the scan movement is increased only in the vertical direction, and the scan order is increased in the horizontal direction. 1. An orthogonal transform encoding device comprising scan order setting means for setting a large number of scan movements only in the horizontal direction when the distribution is widened. (2) When inversely scanning the scanned and one-dimensional coefficients into a two-dimensional array, the scanning order is adjusted to match the occurrence distribution of non-zero coefficients, and if the distribution spreads in the vertical direction, only the vertical direction is used. An orthogonal transform decoding device characterized by having a scan order setting means that increases the number of scan movements and sets the number of scan movements only in the horizontal direction when the distribution spreads in the horizontal direction.