JP3191462B2 - High efficiency coding device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-efficiency coding apparatus for compressing 0 data, which frequently occurs in orthogonally transformed (mainly discrete cosine transformed) image data, using a block run length method.

[0002]

2. Description of the Related Art An orthogonal transform such as a discrete cosine transform (D
In the compression of CT) image data, a block run length method has been proposed in order to compress 0 data which occurs very frequently.

For example, in discrete cosine-transformed image data, data is often concentrated in a low frequency band, and as shown in FIG. 3, many 0 data are generated mainly in a high frequency component. The example of FIG. 3 is an example in which a screen of one frame is divided into two-dimensional blocks (8 lines × 8 pixels) and subjected to discrete cosine transform. Since transmission of this 0 data using an entropy code such as a Huffman code is not advantageous in terms of the amount of information, data compression is usually performed using a run-length code.

[0004] The block run length method is also a kind, and as shown in FIG. 4, the coefficient data obtained by the discrete cosine transform is an area LA containing data other than 0 data.
(Indicated by a thick frame), all data is divided into an area LB of 0 data, only the data of the area LA is transmitted together with the range setting information indicating the range, and the data of the area LB is completely Not transmitted. In this case, since one block is (8 lines × 8 pixels) as described above, the range setting information is 3-bit data indicating a horizontal (H) address and 3-bit data indicating a vertical (V) address. Be composed.

[0005]

By the way, in order to increase the compression efficiency, the screen of one frame is often divided into two-dimensional blocks and subjected to discrete cosine transform (intra-frame DCT) as described above. When there is a motion in the image data, the energy does not concentrate on the low frequency band but remains on the high frequency band as shown in FIG. In this case, in the normal block run length method, an area LA (indicated by a thick frame) including data other than 0 data and an area LB where all data are 0 data are as shown in the drawing. In many cases, the range of the area LB is narrowed and the data compression efficiency does not increase.

Generally, when there is motion in image data in a block, when discrete cosine transform is performed, data other than 0 among coefficient data obtained by the transform is indicated by hatching in FIG. Often concentrated as shown. As described above, the block run length method improves data compression efficiency when energy is concentrated in a low-frequency portion.

Accordingly, the present invention provides a high-efficiency coding apparatus that improves the data compression efficiency by the block run-length method even when there is motion in image data in a block.

[0008]

According to the present invention, there is provided an orthogonal transformation means for transforming input image data into blocks over two fields constituting one frame to perform orthogonal transformation, and a motion detection means for detecting a motion in each block. The transformed data output from the orthogonal transform means corresponding to the block in which the motion is detected by the motion detecting means has an apparently low energy.
Arranging means for rearranging the data so as to concentrate on the area, and transmitting data of a predetermined range of the conversion data of each block output from the arranging means together with range setting information and motion information indicating the predetermined range. is there.

[0009]

According to the present invention, when there is a motion in the image data in the block, the converted data is rearranged by the arranging means, so that the energy is apparently concentrated in the low-frequency portion. Therefore, the data compression efficiency by the block run length method is improved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. In this example, a discrete cosine transform (DCT) is performed as an orthogonal transform.

In FIG. 1, a digital video signal SV is supplied to a blocking circuit 1. This blocking circuit 1
As a result, the video signal SV is converted into a continuous signal for each two-dimensional block which is a unit of encoding. One block is
Over two fields that make up one frame (8 lines x
8 pixels).

The data of each block output from the blocking circuit 1 is supplied to a discrete cosine transform circuit (DCT circuit), where a discrete cosine transform (intra-frame DCT) is performed. The coefficient data output from the DCT circuit 2 is supplied to a line sorting circuit 3 and also to a motion detection circuit 4.

The motion detecting circuit 4 detects whether or not there is a motion in the image data in each block. In this case, the detection of the motion is determined based on the distribution of the coefficient data. That is, when there is motion in the image data in the block, the energy is not concentrated in the low frequency band but remains in the high frequency band as described above (see FIG. 5), so that the motion detection is performed based on the distribution of the coefficient data. It is possible to do. Note that the motion may be detected based on the level of the video signal SV.

The operation of the line sorting circuit 3 is controlled by the detection output of the motion detection circuit 4. That is, a block having a motion in the image data in the block (hereinafter, referred to as a block)
In the “motion block”, the lines are rearranged with respect to the coefficient data of 8 lines × 8 pixels constituting the block so that the arrangement of the four lines on the high frequency component side is reversed, and output. You. For example, when the coefficient data of the motion block is as shown in FIG. 5, it is rearranged as shown in FIG. On the other hand, in a block in which the image data in the block does not move (hereinafter, referred to as a “still block”), the coefficient data is not rearranged as described above, and the coefficient data output from the DCT circuit 2 is output as it is. .

In the line sorting circuit 3, in the case of a motion block, lines are rearranged as described above, so that energy is apparently concentrated in a low-frequency portion. In the case of a stationary block, energy is originally concentrated in a low-frequency portion.

The coefficient data output from the line sorting circuit 3 is supplied to a quantization circuit 5 and is quantized.
The quantized data output from the quantization circuit 5 is coded by the variable length coding circuit 6 and then output as code data DT.

The coefficient data output from the line sorting circuit 3 is supplied to a data amount calculation circuit 7.
In the data amount calculation circuit 7, the data amount when the coefficient data output from the line sorting circuit 3 is quantized by a certain rule is calculated in advance, and the data amount becomes equal to or less than the target value (data transmission capacity of the transmission line). Thus, the quantization step width is determined. Since the portion that becomes substantially zero data varies depending on the quantization step width, the data amount calculation circuit 7 also sets the transmission range of the coefficient data of each block in relation to the quantization step width. In FIG. 2, a region surrounded by a thick frame indicates an example of a transmission range.

Numeral 8 denotes a quantization limiting circuit.
, The coefficient data in the transmission range set by the data amount calculation circuit 7 is controlled to be quantized with the quantization step width determined by the data amount calculation circuit 7. As a result, buffering control is performed so that the transmission rate of the code data DT output from the variable length encoding circuit 6 becomes a predetermined value. The change of the quantization step width is performed, for example, by changing a quantizer selected from a plurality of quantizers having different quantization step widths constituting the quantization circuit 5.

The motion detection circuit 4 outputs 1-bit motion information Dm indicating whether each block is a motion block or a still block. The data amount calculation circuit 7 outputs range setting information Da of 6 bits (each of the horizontal and vertical addresses is 3 bits) indicating the transmission range of the coefficient data for each block. These information D
m and Da are the above-described code data DT as additional bits.
And is used for decoding on the receiving side.

As described above, in the present embodiment, the line sorting circuit 3 rearranges the coefficient data for the motion block so that the energy is apparently concentrated in the low-frequency portion. Can increase the data compression efficiency.

In the above embodiment, an example is shown in which discrete cosine transform (DCT) is performed as orthogonal transform. However, the present invention is naturally applicable to other types of orthogonal transform. .

[0022]

According to the present invention, when there is a motion in the image data in a block, the converted data is rearranged by the arranging means, so that energy is apparently concentrated in the low-frequency portion. There is an effect that the data compression efficiency by the block run length method can be greatly improved.

[Brief description of the drawings]

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

FIG. 2 is a diagram for explaining rearrangement of coefficient data.

FIG. 3 is a diagram illustrating an example of coefficient data obtained by performing discrete cosine transform;

FIG. 4 is a diagram for explaining a block run length method.

FIG. 5 is a diagram illustrating an example of coefficient data when image data in a block has a motion.

FIG. 6 is a diagram for explaining a concentration area of data other than 0 data when image data in a block has a motion.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Blocking circuit 2 Discrete cosine transformation circuit 3 Line sorting circuit 4 Motion detection circuit 5 Quantization circuit 6 Variable length coding circuit 7 Data amount calculation circuit 8 Quantization limiting circuit

Claims (3)

(57) [Claims] 1. An orthogonal transformation means for dividing input image data into blocks over two fields constituting one frame to perform orthogonal transformation, a motion detection means for detecting a motion in each block, and a motion detection means for detecting motion in each block. in response to detected block transform data outputted from said orthogonal transform means, that
Arranging means for rearranging the energy so that the energy is apparently concentrated in the low-frequency portion. A high-efficiency coding apparatus characterized by transmitting information together with information. 2. The high-efficiency encoding apparatus according to claim 1, wherein said motion detecting means detects a motion from level information of said input image data. 3. The high-efficiency encoding apparatus according to claim 1, wherein said motion detecting means detects a motion from distribution information of said transformed data output from said orthogonal transform means.