JPS62220082A - Picture encoding device - Google Patents

Abstract

PURPOSE:To reduce the whole of information quantities, and to reduce the capacity of a buffer memory, by providing a quantization characteristic switching circuit which makes small a quantizing step at the center part of a picture, and makes large the quantizing step at the peripheral part of the picture. CONSTITUTION:An area detection circuit 8 identifies the center part of the picture from the peripheral part of the picture by counting the synchronizing signal of a television signal. The identification signal of the detection circuit 8 is supplied to a quantization characteristic switching circuit 22, and switches a quantization characteristic at the center part, and the peripheral part of the picture. In other words, quantization with a small step and high accuracy is performed at the center part of the picture, and the quantization with a large step and low accuracy is performed at the peripheral part. By constituting a device in such a way, the whole of the information quantities can be reduced, thereby, the capacity of a buffer memory 3 can be reduced.

Description

[Detailed Description of the Invention] [Summary] In encoding image signals, the amount of information can be reduced by coarsening the quantization step in the peripheral area of the screen, making it possible to compress the transmission bandwidth, and improving the accuracy in the central area. This improves the image quality.

[Industrial application field]

The present invention relates to an improvement of an image signal encoding device.

Since images contain a large amount of information, transmitting the image information as is requires a broadband transmission path. Therefore, in order to transmit a large amount of information using a limited frequency band, it is desirable to reduce the amount of information and compress the band.

[Conventional technology]

Image information is quantized and encoded during transmission. Traditionally,
There is a method of switching quantization characteristics for band compression during this encoding.

FIG. 3 is a block diagram of a conventional encoding device.

The analog image signal of the human input signal is supplied to an analog-to-digital conversion circuit 1 and converted into a digital signal using a sampling clock signal, and the converted digital signal is quantized and encoded in a quantization characteristic switching circuit 2.

After the encoded image signal is stored in the buffer memory 3, it is sent out to the transmission path.

When data is generated from a static part of the image with a small amount of effective information and a dynamic part with a large amount of information but a small area, the signal becomes non-uniform and the signal on the transmission path becomes intermittent. Therefore, the buffer memory has the function of preventing the signals on the transmission line from becoming intermittent and homogenizing them.

The memory capacity of the buffer memory is generally selected to a value that can accommodate the number of bits transmitted during one field or one frame period.

However, since the amount of information stored is limited by the capacity of the buffer memory, the buffer memory 3 supplies a quantization characteristic control signal to the quantization characteristic switching circuit 2 to change the quantization characteristic according to the amount of stored data. change.

The characteristic switching of the quantization characteristic switching circuit 2 is performed when a horizontal synchronization signal is detected in the image signal. That is, as shown in FIG. 3a, the quantization characteristics are switched at the Δ point of each horizontal synchronization signal.

When a control signal is applied to the quantization characteristic switching circuit 2 according to the storage capacity of the buffer memory 3, and at the same time a detection signal is applied from the horizontal synchronization signal detection circuit 4 to the switching circuit 2, the quantization characteristic is switched.

In the conventional device, the allocation of quantization characteristics changes in units of horizontal synchronization signals, and band compression is performed each time the amount of stored image information is controlled so as not to exceed the storage capacity of the buffer memory 3.

[Problem that the invention seeks to solve]

In the conventional device described above, the quantization characteristics are the same for all pixels on one horizontal scanning line, and the quantization step is fixed.

However, when image information is displayed and observed on a monitor device,
Due to the visual characteristics, even if there is a difference in the quantization characteristics between the periphery and the center of the screen, the content can be made so that no change is perceived in terms of image quality, so it is possible to create a difference in accuracy in quantization. . Conventional devices do not take this point into consideration.

[Means for solving problems]

As shown in the principle diagram of the present invention in FIG. 1, the above problem is solved when a television signal is converted into a digital signal in an analog-digital conversion circuit 1 and then quantized, a quantization characteristic switching circuit 22 is provided, and By detecting the scanning area from the television signal using the area detection circuit 8, the quantization of the central part 11 of the screen is performed in small steps according to the position of the scanning screen, as shown in FIG. This problem is solved by the image encoding device of the present invention configured to have a quantization characteristic and switch the quantization of the peripheral portion 12 to a quantization characteristic with a large step.

[Effect]

The area detection circuit 8 according to the present invention can detect pixel positions and horizontal scanning line positions by providing a television signal synchronization signal detection section and a detected synchronization signal counting section.

This area detection circuit 8 includes a screen center portion 11 and a screen peripheral portion 12.
Therefore, by supplying the output signal from the detection circuit 8 to the quantization characteristic switching circuit 22, it is possible to switch the quantization characteristic between the central part 11 and the peripheral part 12 of the screen in FIG. It is possible to change the quantization step depending on the pixel position even on the horizontal scanning line.

Note that the quantization characteristic of the quantization characteristic switching circuit 22 is controlled according to the storage state of the buffer memory 3, as in the conventional case.

In this way, the central part of the screen is quantized with small steps and high precision, and the periphery is quantized with large steps and low precision, making it possible to reduce the overall amount of information. , it is possible to provide more buffer memory capacity. Moreover, this makes it possible to further refine the quantization steps in the central part of the screen, which is important in terms of visual characteristics, to increase precision and improve image quality.

〔Example〕

The present invention will be described in detail with reference to the illustrated embodiments.

FIG. 2 shows a block circuit diagram of an embodiment of the encoding device of the present invention.

In the figure, 5 is a vertical synchronization signal detection circuit, 6 and 7 are counters, 22 is a quantization characteristic switching circuit, and other circuit parts that are the same as those in FIG. 3 are designated by the same numbers.

The horizontal synchronization signal detection circuit 4 supplies the detection signal as a load signal to the counter 6 and resets the counter 6. Counter 6 operates as a pixel counter.

As the clock signal of the counter 6, a sampling clock signal sent to the analog-to-digital conversion circuit 1 is used.

The counter 6 has output parts of Qa, Qb, and Qc. For example, when the count value A, [1, C is reached, the quantization characteristic switching circuit 2
The quantization characteristics of 2 are switched by the A, B, and C signals. The vertical synchronization signal detection circuit 5 uses the detection signal to reset the counter 7 and start counting.

The count clock signal of Carantuff is given from the horizontal synchronization signal detection circuit 4. The counter 7 operates as a line counter for horizontal scanning lines.

The count value of the counter 7 is given as a load input to the pixel counter 6. Signals A, B output from counter 6,
The output point of C changes depending on the load value from the counter 6, and the pixel position at which the quantization characteristic is switched can be changed for each scanning line.

In this way, the quantization characteristics are switched even on the same horizontal scanning line.

FIG. 2a shows a quantization characteristic switching point and an image signal waveform diagram according to the encoding method of the present invention, and the quantization characteristic is A.

For coarse step quantization between B and between C and A, and B
, C, the quantization is switched to small steps.

In this way, the quantization can be made coarser in the peripheral areas of the screen, that is, in the upper, lower, left, right, and winter areas of the screen, and the central area, which is important in terms of visual characteristics, can be quantized with high precision.

〔Effect of the invention〕

According to the present invention, high image quality can be easily achieved without increasing the buffer memory capacity, and its effects are extremely large.

[Brief explanation of drawings]

Fig. 1 is a diagram of the principle of the present invention, Fig. 1a is an explanatory diagram of the operation of the present invention, Fig. 2 is a block circuit diagram of an embodiment of the encoding device of the present invention, Fig. 2a is a diagram showing the code and ossification device of the present invention. Quantization characteristic switching point and image signal waveform diagram FIG. 3 is a block diagram of a conventional encoding device, and FIG. 3a is a quantization characteristic switching point and image signal waveform diagram of the conventional encoding device. In the figure, ■ is an analog-to-digital conversion circuit, 2.22 is a quantization characteristic switching circuit, 3 is a buffer memory, 4 is a horizontal synchronization signal detection circuit, 5 is a vertical synchronization signal detection circuit, 6.7 is a counter, and 8 is a In the area detection circuit, 11 indicates the center part of the screen, and 12 indicates the peripheral part of the screen. Figure 1 12 Center of the screen! @ ] Figure a A B d A Figure 2a

Claims (1)

[Claims] An area detection circuit (8) detects the center part (11) and peripheral part (12) of the screen of the television signal, and quantization of the center part (11) of the screen is performed in small steps using signals from the detection circuit. A quantization characteristic switching circuit (2
An image encoding device comprising: 2).