JPH0273793A - High efficient coding device - Google Patents

Abstract

PURPOSE:To reduce the sent data quantity and to attain the transmission of a picture with high picture quality in a visual sense by increasing the number of coded bits for a picture element in the middle of each pattern and decreasing the number of coded bits for picture elements at the surrounding part. CONSTITUTION:Since the sensitivity is visually low at the peripheral part in comparison with the middle of the pattern in general, the number of coded bits of each picture element in the middle of each pattern is increased more than the number of coded bits of each picture element at the end of the pattern. That is, for example, a 3-bit code is assigned to each picture element of an area (a) (3rd area), a 4-bit code is assigned to each picture element of an area (b) (2nd area) and a 5-bit code is assigned to each picture element of an area (c) (1st area). Thus, the data compression rate is increased in the peripheral part to send a picture data with high quality visually and the data compression rate is increased.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a high-efficiency encoding device, and more specifically to a high-efficiency encoding device used when compressing the amount of information of an image signal and transmitting it digitally. Regarding.

[Conventional technology]

When digitally transmitting image information, various encoding methods have been proposed to reduce the amount of data to be transmitted. One such method is predictive differential coding (hereinafter referred to as DPCM), which aims to compress the amount of information by utilizing the correlation between adjacent sample values. Specifically, in this encoding method, an encoded sample value is once decoded, the decoded value is used to obtain a predicted value for the next sample value, and the error between this predicted value and the actual value is calculated by quantization. and encode it. FIG. 8 shows a block diagram of the configuration of an encoding device for the simplest prior value predictive encoding.

The sample value Xi input to the input terminal IO is applied to the subtracter 12, where a predicted value (previous value decoded value in this example), which will be described later, is subtracted therefrom. The quantizer 14 quantizes the difference value output from the subtracter 12 and outputs it to the output terminal 16 as a DPCM code Yi. This DPCM code Yi is also applied to the inverse quantizer 18. The inverse quantizer 18 decodes the DPCM code Yi into a difference value and applies it to the adder 20. The adder 20 adds the previous predicted value applied to the subtracter 12, thereby restoring the difference value to the locally decoded value corresponding to the sample value. The limiter 22 limits the amplitude of the output of the adder 20 to a predetermined range and supplies it to a D-type flip-flop 24 .

The output of the D-type flip-flop 24 becomes a predicted value for the next sample value, and is supplied to the subtracter 12 and adder 20. Generally, the distribution of difference values from previous predicted values is biased toward small values, and by encoding the difference values, information can be compressed. Furthermore, it is known that the broken line portion 26 in FIG. 8 can be converted into a memory table.

[Problem that the invention seeks to solve]

By the way, in recent years, so-called high-definition television (HDTV)
There is a desire for higher definition images, such as standardization of signals.

Along with this, the amount of data transmitted per unit time during digital transmission also increases dramatically, causing difficulties in digital transmission, recording and reproduction, etc. Therefore, it is desirable to perform even higher information compression during high-efficiency encoding, but there is a limit to the improvement in compression rate during predictive encoding described above. For example, if each pixel is sampled with 8 bits and then predictively encoded to produce a 4-bit code, if it is changed to a 3-bit code, the quantization noise becomes thick (and the deterioration of image quality becomes noticeable).

The present invention was made against this background, and it is possible to transmit visually higher-quality images without reducing the data compression ratio, or to increase the data compression ratio without reducing the image quality. The purpose of this invention is to provide a high-efficiency encoding device.

[Means for solving problems]

For this purpose, according to the present invention, the number of encoding bits of each pixel in the first area located at the center of each screen is increased compared to the first area located at the edge of the screen. The number of encoding bits for each pixel in the second area is made larger than that in the second area.

[For production]

Generally, the peripheral area has lower visual sensitivity than the center of the screen, so it is not a good idea to encode the entire screen using the same encoding method, and it is recommended to increase the data compression rate even higher in the peripheral area. desirable.

In accordance with this, the present invention makes it possible to visually transmit high-quality image data and increase the data compression rate by making the number of encoding bits for each pixel in the center of the screen larger than that in the periphery. It became.

〔Example〕

FIG. 1 is a conceptual diagram showing an embodiment of the present invention, in which the screen is divided into nine areas and differential encoding codes are assigned according to each area. For example, each pixel in the area a (third area) in the figure has a 3-bit code, each pixel in the area b (second area) has a 4-bit code, and the area C (
A 5-bit code is assigned to each pixel in the first area).

FIG. 2(A) is a block diagram of a transmission system including an encoder which is an embodiment of the present invention. The operation will be explained below using this block diagram. In this embodiment, the data compression ratio is switched between three types by region division.

The device of this embodiment uses a vertical synchronization signal (VD) to divide the image into regions.
), and a control circuit 2 which is generated from a horizontal synchronizing signal (HD). The circuit 2 generates control signals for the switches SWI and SW2 based on HD and VD. This causes the switch SWI to change the input value Xi to the area a in FIG.
In the case of a pixel in the area A, the pixel is connected to the terminal a, and in the case of a pixel in the area C, it is connected to the terminals A and C, respectively. Here, the output of the control circuit 2 is specifically a 2-bit code.

4a, 4b, and 4c are DPCM tables, respectively;
These are the sample values of pixels in each area a, b, c
i (8 bits) are respectively input, and a 3.4.5 bit encoded code and an 8 bit locally decoded value are output.

6a, 6b, and 6c are previous value predictors, which delay the local decoded value Xi corresponding to the immediately previous sample value by a predetermined period and output it as a predicted value Xi. These previous value predictors 6a
, 6b, and 6c are the local decoded values from the DPCM table that encodes the immediately preceding target value as shown in FIG.
) 61, and the DF/F 61 delays it for a predetermined period. This switch SW3 is controlled by the output d of the control circuit 2.

Therefore, if the target value to be encoded and the sample value immediately before it exist in the same area, each table 4a, 4
b and 4c use the locally decoded values output by themselves to obtain predicted values, but even if the sample value to be encoded and the sample value immediately before it are in different regions, they can also be output from other tables. The configuration is such that a predicted value can be formed using locally decoded values.

As a result, even when switching the area where the sample value exists,
DPCM encoding can be performed continuously, and there is no need to reset DPCM encoding. When this reset is performed, an 8-bit sample value must be transmitted once, so
Since DPCM encoding can be performed continuously, the amount of data to be transmitted can be reduced, and the overall data compression rate can be increased.

The encoded code outputted from any one of the tables 4a, 4b, and 4c is outputted in time series by the switch SW2 and supplied to the buffer memory 7. 3 to 5 bit parallel data is input to the buffer memory 7, and is outputted as serial data of a constant period. The delay time of the parallel data in the buffer memory 7 at this time is appropriately determined using the output of the control circuit 2 for controlling the switch SW2.

The code output from the buffer memory 7 is supplied to a synchronization and ID addition circuit 8, which adds additional data (ID) including bit synchronization data and identification data indicating which region of pixels the code corresponds to. and sent out to the transmission path.

Next, the configuration of the receiving system corresponding to the transmitting system shown in FIG. 2 will be explained using FIG. 3. DPCM supplied from transmission line
The code data string is input to the synchronization and ID separation circuit 9 and the buffer memory 17. The synchronization data separated by the synchronization/ID separation circuit 9 is supplied to the buffer memory 17, and the timing for data acquisition of the memory 17 is determined. Further, the aforementioned identification data in the ID separated by the circuit 9 is supplied to the control circuit 2'.
The output switch SW4. Determine the control timing of SW5. Further, the buffer memory 17 is also controlled using the output of the control circuit 2', and 3 to 5 bit parallel data is sequentially outputted from the buffer memory 17 at a predetermined timing.

The switch SW4 sends the output data of the buffer memory 17 to three DPs as appropriate depending on the number of bits of the data, that is, the code corresponding to the pixel in the area a, b, or c in FIG.
It is supplied to one of the CM decoding tables 3a, 3b, and 3c. The decoded value output from any one of the decode tables 3a, 3b, and 3c is output from the switch SW5 as an output value Xo. Previous value predictors 5a, 5b, 5 have a function of delaying the output of this switch SW5 for a predetermined period.
c through each decoding table 3a, 3b.

Returned to 3c. Therefore, regardless of whether the number of bits of the encoded code input to the switch SW4 is 3 to 5 bits, the previous decoded value is always supplied to each decoding table 3a, 3b, and 3c, and the decoded value is continuously supplied. It is possible to perform DPCM decoding. For example, the encoded code input to the switch SW4 and the previous value predictors 5a and 5b
, 5c correspond to pixels in different areas in FIG. 1, the decoded values can be obtained.

In the encoding/decoding device configured as described above, a large number of bits are allocated to encoding codes corresponding to pixels in the central area of the screen, and codes corresponding to pixels in the peripheral area of the screen are assigned a large number of bits. By allocating a smaller number of bits to the encoded code, it is possible to transmit visually high-quality images with the same amount of data, and it is possible to transmit images with the same visual quality with a smaller amount of data.

In addition, DPC
The configuration is such that M encoding can be performed, so that the number of resets for DPCM encoding does not increase (and the amount of transmitted data does not increase accordingly).

Next, other embodiments of the present invention will be described. FIG. 4 is a diagram showing the configuration of a transmitting system including an encoding device as another embodiment of the present invention, and FIG. 5 is a diagram showing the configuration of a receiving system corresponding to the transmitting system in FIG. Components in FIGS. 4 and 5 that are similar to those in FIGS. 2 and 3 are designated by the same numbers.

In the embodiments described above with reference to FIGS. 2 and 3, each area a.

A separate DPCM loop is operated for each of b and c, and when these loops are switched, the previous value predictor is also switched for receiving and receiving locally decoded values related to the previous sample value.

In contrast, in the embodiments shown in FIGS. 4 and 5, one system of prior value predictors corresponds to three types of DPCM loops. That is, the input signal Xi
are encoded tables 4a, 4b,
4c, and the local decoded values output from each table are selectively used in the previous value predictor 6 to obtain one predicted value. This predicted value (8 bits) is the same for all encoding tables, and the predicted value output from the predictor 6 is supplied to all of the tables 4a, 4b, and 4c.

Further, in FIG. 5, the decoded value output from the switch SW5 is delayed by a predetermined period of time by a single previous value predictor 5, and then converted into a predicted value and sent to each decoding table 3a, 3b.

3c.

In the embodiments shown in FIGS. 4 and 5, the same effects as in the embodiments shown in FIGS. 2 and 3 can be obtained, and the circuit configuration can be further simplified.

FIG. 6 is a block diagram of a transmitting system including an encoding device as still another embodiment of the present invention, and FIG. 7 is a block diagram of a receiving system corresponding to FIG. 6. In FIGS. 6 and 7, the same components as in FIGS. 1 and 2 are designated by the same numbers.

In Fig. 6, numeral 31 is a lookup table that receives as input an 8-bit sample value, an 8-bit predicted value, and 2-bit data indicating one of areas a, b, or c. switches SWI, SW2, table 4a,
4b, 4c, and a predicted value selection function for the previous value predicted value 6. That is, this look-up table 31 functions as a composite DPCM table, and outputs an effective 3- to 5-bit encoded code and an 8-bit locally decoded value. The previous value predictor 32 delays the local decoded value output from the table 31 for a predetermined period and uses it as a predicted value in the table 3.
1 input.

When the input sample value Xi corresponds to a pixel in the area a, the composite D P CM table 31 is set to table 4a in FIGS. 2 and 4 according to the 2-bit data from the control circuit 2.
Similarly, when the sample value corresponding to the pixel in area C is input, the output is the same as table 4b, and when the sample value corresponding to the pixel in area C is input, the output is the same as table 4c. I do.

In addition, the look-up table indicated by 33 in FIG. The previous decoded value) is input and an 8-bit decoded value is output. Along with the above-mentioned identification data, the control circuit 2' inputs a 2-bit code indicating the area to which the pixel corresponding to the encoded code belongs to the table 33.
3 outputs the same decoded value as any of tables 3a, 3b, and 3c in FIG. That is, table 31 acts as a composite DPCM decoding table.

The embodiments shown in FIGS. 7 and 8 also provide the same effects as the previously described embodiments. Also, although the look-up table requires a large memory capacity, it can be processed in an extremely short time, especially for high-data-rate image signals that require high-speed processing, such as HDTV signals. suitable for processing.

〔Effect of the invention〕

As explained above, according to the present invention, the amount of data to be transmitted is increased by increasing the number of encoding bits for pixels in the center of each screen and decreasing the number of encoding bits for pixels in the peripheral area. This makes it possible to transmit images with low visual quality and high visual quality.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram for explaining the concept of an embodiment of the present invention. FIG. 2 is a block diagram showing the configuration of a transmission system including an encoding device as an embodiment of the present invention. 2 is a block diagram showing the configuration of a receiving system corresponding to the transmitting system in FIG. 2, FIG. 4 is a block diagram showing the configuration of a transmitting system including an encoding device as another embodiment of the present invention, and FIG. 6 is a block diagram showing the configuration of a receiving system corresponding to the transmitting system shown in FIG. 6. FIG. FIG. 8 is a block diagram showing the configuration of a receiving system corresponding to the transmitting system in the figure. FIG. 8 is a diagram showing an example of the configuration of a conventional DPCM encoder. In the figure, a, b, and c are the third, second, and first regions, respectively.
SWI to SW5 are switches, 2 is a control circuit, 4a, 4b, and 4c are DPCM tables, 6. 6
a. 6b, 6c, 34 are previous value predictors, 3■ is composite DPC
This is an M table.

Claims (3)

[Claims] (1) The number of encoding bits of each pixel in the first area located at the center of each screen is compared to that of each pixel in the second area located at the edge of the screen. A high-efficiency encoding device characterized in that the number of encoding bits is larger than that of a pixel. (2) The number of encoding bits of each pixel in a third area located further toward the edge of the screen compared to the second area is the number of encoding bits of each pixel in the second area. 2. A high-efficiency encoding device according to claim 1, wherein: (3) Each pixel is encoded by a predictive encoding means capable of calculating a predicted value of a pixel in the second or first region using the locally decoded value of the pixel in the first or second region. A high-efficiency encoding device according to claim (1).