JPS6245751B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to an image signal processing method.

[Technical background of the invention and its problems]

For example, when transmitting a television image signal through some kind of transmission line, the image signal is digitally encoded and transmitted in order to prevent noise components from being mixed in the transmission line.

However, with such means, the amount of data to be transmitted is generally large, and the time required for transmission is enormous.

This problem appears in different forms not only when transmitting image signals, but also when storing image signals. For example, when storing image signals, a large capacity memory is required due to the enormous amount of information in the image signals.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an image signal processing method that eliminates the above drawbacks and can accurately represent an image with a smaller amount of information without degrading the image quality.

[Summary of the invention]

The present invention is an image signal processing method that converts a first signal representing an image into a second signal and reproduces an image from this second signal. This is to change the signal amount when converting the first signal to the second signal.

The quality of an image is defined as the amount of information in the image. The amount of information in an image is, for example, the density of the image. At this time, if the image is determined to be dense, when converting the first signal representing the image into the second signal, the first signal is represented by the first signal amount. If the image is determined to be rough, the image is expressed with a smaller signal amount than the first signal amount when converting the first signal representing the image into a second signal.
More specifically, a large number of bits is used in areas where the image changes rapidly, and a smaller number of bits is used in areas where the image changes slowly, to convert the signal representing the image.

〔Effect of the invention〕

According to this invention, since the amount of signal expression is changed depending on the amount of information in the image, the amount of information required for image reproduction can be reduced even though the quality of the reproduced image is not impaired in any way. . This allows the system to which the invention is applied, for example, to reduce the amount of information to be transmitted or to require less memory storage capacity.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of this embodiment, where a indicates the transmitting side and b indicates the receiving side. 1 is an image input device such as a camera, 2 is an AD converter that digitizes an image signal output from the image input device 1, and 3 is a memory device that stores information for one screen of images.
Reference numeral 4 denotes a density discrimination circuit for discriminating dense parts and coarse parts of image information from this image data, the details of which will be described later. 5, 6, and 7 are all encoders, 5 is for encoding the coarse/fine boundary information, and 6, 7 is for encoding the portion of the image determined to be dense or coarse by the coarse/fine discriminating circuit 4. This is an encoder for performing 6 and 7 can be shared by the same encoder. The image signals encoded by the encoders 5, 6, and 7 are temporarily stored in a buffer memory 8, and sent to a modulation device 9 for each screen to be sent out to a modulated transmission path.

A modulated image signal sent from the transmitting side is demodulated by a demodulator 11 and temporarily stored in a buffer memory 12. Among the encoded signals that have entered the buffer memory 12, information at the boundary between the density and density of the information is first
The signal is input to a decoder 13 and decoded. The decoded boundary information is sent to the control circuit 14, and the decoders 15, 16 are sent from the buffer memory 12 according to this information.
The encoded signal of the dense part of the information supplied to the memory 7 is controlled, and image information for one screen is obtained in the memory 7. This information is converted into an analog signal by the DA converter 18 and reproduced on the monitor 19.

The details of the density discrimination circuit 4 will be described below. The memory 3 stores bit data encoded into 8-bit PCM from the AD converter 2. Incidentally, in order to save the memory capacity, a DPCM code of about 4-5 bits may be used. In this case, the AD converter 2 and memory 3 parts are, for example, as shown in FIG. 2a or
The configuration is shown in b. At a, the signal is digitally DPCM encoded by the AD converter 2 and stored in the memory 22. When DPCM encoded like this, memory 2
Memory 2 requires about half the capacity of memory 3. The data stored in this memory 22 is sent to the DPCM decoder 2.
The signal is decoded at step 3 and supplied to the coarse/fine discriminator circuit 4.

On the other hand, FIG. 2b shows a case where an analog DPCM encoder 24 is used, and after this encoding, the data is stored in the memory 25, and
After being decoded by the analog DPCM decoder 26, it is supplied to the density determination circuit 4. In this case, the AD converter and DA converter are not required.

Returning to the embodiment shown in FIG. 1, the memory 3 stores, for example,
One screen worth of image data consisting of 512 x 512 pixels is stored. Such one screen of image data is divided into blocks of 8 x 8 points, for example, and changes in the image data are examined within the blocks thus divided. Two examples of one block of 8×8 points are shown in FIGS. 3a and 3b. a is a block with little change in pixel value, and is approximately 0 to 2. For example, the absolute value of the difference between two horizontally adjacent pixels may be used to determine the density of the image information. In figure b, the difference between these two pixels is
There are 38 items, which shows that the information is dense.

Concentration determination circuit 4 when performing density determination based on the difference between two horizontally adjacent pixels as described above
An example of this is shown in FIG. Data xn input one after another in the horizontal direction is delayed by the delay circuit 31.
It becomes xz−1. This data xn-1 is the subtraction circuit 3
2 and the change Δ=xn−xn−1 is generated. In the determination circuit 33, the sum of these Δs within one block is calculated, and then a determination is made based on the policy described above. That is, if the sum is equal to or greater than a certain value, the information is determined to be dense.

In this way, all 4096 blocks are subjected to density determination, and an address code representing a dense block is created in the encoder 5. This address code is as follows. For example, the dense blocks shown in Figure 5 are 3rd from the left and 7th from the top.
Similarly, when the numbers are 4th and 10th, the positions (3, 7) and (4, 10) are encoded. A commonly used run-length code may be used for this encoding, an example of which is shown in FIG.

The position (3, 7) of the first dense block is represented by (1001, 11001) in the above code. It is sufficient to express the distance from the previous such block to the position of the second dense block of information, and there is no need to encode the absolute position. That is, in the above example, 4-3=1 and 10-7=3, which means (1, 3), and when encoded, it becomes (01, 1001). In this way, an information code indicating a dense portion of image information is created in the encoder 5.

Next, encoders 6 and 7 encode dense or coarse blocks of information. As the encoding method, for example, a linear transform encoding method, DPCM, or ΔM encoding method can be used. In the case of linear transformation coding, the encoder 6 performs high-quality encoding of, for example, 4 to 5 bits per sample, and the encoder 7 performs low-quality encoding of, for example, 1 to 2 bits. Bye. Although the condition of the image is different, the ratio of blocks with dense information as described above is 25% of the entire screen, and the number of bits used in the encoder 6 for encoding blocks with dense information is 4 bits per sample. If we set the number of bits in the encoder 7 used to encode coarse blocks to 1 bit per sample, and set the address code to 0.25 bits/sample, the average is 2 bits/sample, which is about the same as the usual 4 bits/sample. It was confirmed that it is possible to encode

Similarly, when using the DPCM encoding method as shown in Figure 2a, 4-bit DPCM is input to the encoder 6.
If 1-bit DPCM, ie, ΔM, is used in the encoder 7, the transmission efficiency can be similarly increased without deteriorating the image quality.

The bit data encoded in this manner is temporarily stored in the buffer memory 8. Subsequently, the signal is modulated by a modulator 9 and then sent out to a transmission line. still,
When the encoding method of the present invention is used for an image file, the data may be stored from the buffer memory 8 to the image memory. In this case, the capacity of the image memory is significantly reduced, and the quality of the reproduced image is not impaired in any way.

As explained above, in the present invention, the density of image information of one screen is determined as a whole, and the coarse parts are encoded using an encoding method that uses a smaller number of bits than the dense parts. Therefore, the average number of encoding bits can be significantly reduced without affecting the deterioration of the image quality of the entire screen, which has the effect of contributing to shortening transmission time and file capacity.

Although one embodiment of the present invention has been described above, the present invention is not limited to the embodiment in any way. For example, the image processing method according to the present invention is not limited to facsimile transmission and image file devices. That is, the present invention can be applied to all systems that convert a signal representing an image (first signal) into a visible image again.

Furthermore, the encoding system and method are not limited to the embodiments. For example, in the present invention, encoding a coarse portion includes not only selecting encoding suitable for such a portion, but also thinning out pixels and performing the same encoding as that for a dense portion. For example, in ΔM encoding, pixel points may be extracted every other sample without encoding all samples, or every other line may be encoded.

Furthermore, in the present invention, the blocking of the determination of the density of pixel information may not be determined in advance as in the above embodiments, but may be changed depending on the image.
In this way, transmission efficiency can be further improved.

[Brief explanation of the drawing]

1a and 1b are circuit configuration diagrams of a transmitting side and a receiving side to which the encoding method of an embodiment of the present invention is applied; FIGS. 2a and 2b are circuit configuration diagrams of a partial modification of FIG. 1a; 3
Figures a and b are diagrams showing an example of a dense block determined by the present invention, Figure 4 is a diagram showing an example of the configuration of a coarse density determination circuit, and Figure 5 is a diagram showing a block with dense information.
FIG. 6 is a diagram showing an example of a run-length code. 3, 17...Memory, 8, 12...Buffer memory, 4...Sparseness determination circuit, 5, 6, 7...Encoder, 13, 15, 16...Decoder.

Claims (1)

[Claims] 1. means for supplying a first signal representing an image;
An image signal processing method comprising a conversion means for converting a first signal from the means into a second signal, the method comprising a determination means for determining the amount of information of the image represented by the first signal. If the determination means determines that the amount of information in the image is large, the second signal obtained by the conversion means is expressed by the first signal amount, and the determination means determines that the amount of information in the image is small. If so, the second signal obtained by the conversion means is expressed by a second signal amount smaller than the first signal amount, and whether it is expressed by the first or second signal amount. An image signal processing method characterized in that information about the second signal is added to the second signal and output. 2. The image signal processing method according to claim 1, wherein the determining means comprises means for determining the density of the image. 3. A patent characterized in that the determining means includes means for detecting a level difference between first signals representing adjacent pixels in the image, and the density of the image is determined based on the level difference obtained by this means. An image processing method according to claim 2. 4. The image signal processing method according to claim 1, wherein the entire image is divided and the determining means determines the amount of information for each divided element. 5. The image signal processing method according to claim 1, wherein the second signal from the conversion means is used for image reproduction. 6. The image signal processing method according to claim 5, characterized in that the second signal is supplied to the transmission path. 7. The image signal processing method according to claim 5, characterized in that the second signal is stored in a memory.