JPH0586118B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image signal band compression method that can be applied to transmitting or recording image signals.

(Prior art) Conventionally, regarding band compression technology for pixel signals, a technology known as the TAT method was reported in IEICE Communication Method Study Group Material CS84-7 "Time axis conversion band compression method for high-definition television signals". It is being

The TAT method first uses coarse subsampling to extract basic pixels that represent the basic structure of the image.
Next, additional pixels necessary to express the fineness of the image are selected from the remaining pixels.

This corresponds to dividing the image into small blocks and changing the sampling pattern as shown in FIGS. 4a and 4b depending on the fineness of the image within each block. That is, a plurality of modes are set with one sampling pattern as one mode, the mode is switched and assigned to each block according to the fineness of the image, and pixels are thinned out and band compression is performed according to the assigned mode. By doing so, it is possible to reduce the interpolation error as a whole by thinning out pixels in flat parts of the image without thinning out pixels in fine parts of the image. TAT
In determining the mode in the method, when the number of modes is two types shown in Figure 4a and b, as shown in Figure 5, the intra-block sum S of the absolute value of the interpolation error for mode 2 in Figure 4b is calculated. The mode is determined using a histogram of , with a certain value Th of S as a boundary. In other words, blocks exceeding Th are in mode 1.
However, blocks below Th are assigned mode 2.

(Problems to be Solved by the Invention) In the conventional TAT method, the mode for each block is determined by looking only at the histogram of the sum S of interpolation errors, as described above. Therefore, it is not possible to prohibit a certain type of mode or forcibly fix a mode for each block due to factors other than the intra-block sum S of interpolation errors.

It is an object of the present invention to provide pixel signal band compression based on mode determination that allows the selection of a certain type of mode to be prohibited or forced by replacing the interpolation error value of each mode with a predetermined value. The goal is to provide a method.

(Means for Solving the Problems) The image signal band compression method of the present invention thins out pixels on the transmitting side and restores the image by interpolating the thinned out pixels on the receiving side.
A plurality of pixel thinning and interpolation modes are prepared, and when one mode is selected from the plurality of modes, an interpolation error is calculated for each of the plurality of modes from the image signal, and at least one of the interpolation errors is calculated from the image signal. A part of the error is replaced with a predetermined value, and the replaced interpolation error is used to determine the mode.

(Operation) The key point of the present invention is a method for determining a mode in image band compression in which pixels are thinned out on the transmitting side and the thinned out pixels are interpolated on the receiving side to restore the image.

FIG. 1 shows an example of a method for replacing interpolation errors in mode determination of the image signal band compression method of the present invention. For example, when prohibiting the selection of mode i for a certain block, the interpolation error for mode i of that block is replaced with infinity or a value exceeding the maximum value that the interpolation error can take.
If the mode is determined using the TAT method, mode i will not be assigned to that block because the interpolation error for mode i is large. Conversely, when forcing the selection of mode i, the interpolation error for mode i of that block is replaced with 0 or the minimum possible value, and the interpolation error of other modes is set to infinity or the maximum possible value. The mode may be determined by replacing the value with a value exceeding the value and using the conventional mode determination method of the TAT method. That is,
After performing the replacement as shown in FIG. 1, if the replaced interpolation error is used to determine the mode in the same manner as in the conventional TAT method, it becomes possible to prohibit or force selection of mode i.

(Example) Next, an example of the present invention will be described using FIGS. 1 to 4.

In this embodiment, as an example, a television signal is input, the field is divided into blocks each having a size of 4 pixels x 4 pixels, the mode is determined for each block for each field, and the number of pixels is reduced to 1 of the total. The case of thinning out to /2 is shown. In addition, the modes in this embodiment are shown in FIG. 4 a and b as an example.
There are two types, Mode 1 and Mode 2, shown in Figure 1. The compression ratio of each mode is 1 for mode 1 and 1/4 for mode 2.
Mode 2 uses intra-field interpolation.

That is, in this embodiment, two types of modes a and b shown in FIG. 4 are assigned to each block, and corresponding thinning is performed to perform band compression.The mode determination method will be particularly explained below.

FIG. 2 is a block diagram schematically showing the basic part of a transmitting section of a television signal band compression system according to an embodiment of the present invention.

For the image signal 50 input from the input terminal,
Mode 2 decimation and interpolation are performed in mode 2 decimation and interpolation circuit 1, and its output is input to difference circuit 2, where the difference between the interpolated signal and the original signal is calculated.

The difference signal is input to the interpolation error calculation circuit 3, where the sum S of the absolute values of the difference signal within the block is calculated, and this is output as the interpolation error signal 51.

For example, the replacement determination circuit 8 inputs the interpolation error signal 51 and the mode signal 53 which is the mode determination result one field before, and calculates the intra-block sum S of interpolation errors in the block that was in mode 2 one field before. If it is less than a given threshold T1, mode 1 is prohibited in the current field (mode 2 is forced), and if the block was in mode 1 one field ago, and the intra-block sum of interpolation errors S
If it is greater than or equal to a given threshold T2, a determination is made to prohibit mode 2 (forcing mode 1) in the current field, and a replacement determination signal 52 is output.

The interpolation error signal 51 and the replacement determination signal 52 are input to the interpolation error replacement circuit 4, and according to the replacement determination signal 52, part or all of the interpolation error signal 51 is
The interpolation error signal 56 is replaced according to the diagram, and the replaced interpolation error signal 56 is output to the histogram creation circuit 5.
The histogram creation circuit 5 creates a histogram of the replaced interpolation error S' as shown in FIG. The value of S' when it reaches 1/3 or more of the total number of blocks is set as the threshold Th, and Th is output to the mode determining circuit 7.

The mode determining circuit 7 determines the mode for all blocks using the replaced interpolation error signal 56 and the threshold Th. That is, for each block,
Mode 1 is assigned to blocks whose replaced interpolation error S' is greater than or equal to Th, and mode 2 is assigned to blocks where the replaced interpolation error S' is smaller than Th, and the mode signal 53 is assigned.
Output.

The input image signal 50 is delayed by the delay circuit 9 after the input image signal 50 is input until the mode determination circuit 7 determines the mode for each block, and this delayed image signal 54 is sent to the thinning circuit 10. , pixels are thinned out based on the mode signal 53. The thinned-out image signal 55 and the mode signal 53 determined by the mode determining circuit 7 are respectively transmitted from output terminals to the receiving side.

A mode determination method based on this embodiment will be described below.

In the embodiment shown in FIG. 2, the mode is determined for each field, but the mode may be determined for a plurality of fields at once.

Further, before thinning out in the mode 2 thinning interpolation circuit 1 and thinning circuit 10 in FIG. 2, the signal band may be limited in order to prevent aliasing distortion in correspondence with mode 2.

Furthermore, the threshold value in the threshold value determination circuit 6 in FIG.
As a method for determining Th, the contents of the histogram may be read starting from the one with the smallest interpolation error S'. However, in that case, the value of S' when the addition result exceeds 2/3 of the total number of blocks is set as Th.

Further, the types of modes used may be different from those shown in FIGS. 4a and 4b.

According to this embodiment, the signal band of the television signal can be compressed to 1/2, the band of the transmission path required for transmission is reduced to 1/2, and an image signal band compression method with even better image quality is possible. . Note that the compression rate of the image signal can be varied by controlling the compression rate of each mode or the value of Th.

(Effects of the Invention) As described above, according to the present invention, when determining each block mode, by replacing the interpolation error value of each mode with a predetermined value, It becomes possible to prohibit or force choices.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a method for replacing interpolation errors in mode determination according to the present invention, FIG. 2 is a block diagram schematically showing the basic part of a transmitter in an embodiment of the present invention, and FIG. An explanatory diagram showing a mode determination method in an embodiment of the present invention, FIGS. 4a and 4b are
An explanatory diagram showing the sampling pattern of the TAT method,
FIG. 5 is an explanatory diagram showing a mode determination method in the TAT method.

Claims (1)

[Claims] 1 In an image signal band compression method that restores an image by thinning out pixels on the transmitting side and interpolating the thinned out pixels on the receiving side, multiple pixel thinning and interpolation modes are prepared, and one of the plurality of modes prepared is When selecting one mode, an interpolation error is calculated for each of the plurality of prepared modes from the image signal, and at least a part of the interpolation error is replaced with a predetermined value to calculate the replaced interpolation error. A pixel signal band compression method characterized by determining a mode using.