JPH11284864A - Image decoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the image decoder that improves the processing speed for images with a short run length. SOLUTION: Coded data to be decoded are temporarily stored in a coded data temporary storage circuit 3. A code decoder circuit 10 decodes only codes with a predetermined short run length, and decodes code data when the succeeding coded data to be decoded is the short run length code and a code decoder circuit 12 in decodes the next succeeding coded data to be decoded. Since the code decoder circuit 10 is configured to decode only limited codes, the circuit 10 is realized with a small scale circuit configuration and the processing speed is high. Thus, an image with a short run length where a color of the image changes from white to black or vice versa in the unit of one pixel to several pixels such as an image with gradation like a photograph is decoded efficiently at a high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image decoding apparatus, and more particularly, to a phase decoding apparatus for a change point of a run length or a reference line.

[0002]

2. Description of the Related Art As this type of decoding apparatus, for example, an MH, MR, or MMR system, which is an international standard system of facsimile machines, is known. In the run-length entropy coding represented by the MH system of a facsimile apparatus, a short code is assigned to a run-length data having a high frequency of occurrence using a variable-length code, and conversely, to a code having a low frequency of occurrence. The entire data amount is compressed by assigning a long code.

The point at which a pixel changes from white to black or from black to white is called a change point, and the immediately preceding line is called a reference line. In the MR and MMR systems, in addition to run-length coding, a reference line is used. The relative positional relationship between the change point of the line and the decoding processing line is also encoded to realize a higher compression ratio than the MH method.

An example of a conventional image decoding apparatus will be briefly described with reference to FIG. The code data combining circuit 1 receives, for example, 16-bit code data 1A. If the output 2A from the code data shift circuit 2 has a space of 16 bits or more, the code data combining circuit 1 takes in the code data 1A and outputs it to the code data temporary storage circuit 3 as a 32-bit output 3A. The data stored in the code data temporary storage circuit 3 is sent to a code decoder circuit 4 and the code data shift circuit 2. The reference line change point detecting circuit 5 includes a reference line image data 8A and an image restoring circuit 6.
The position of a reference line change point required for decoding is detected from the position data 7A of the restored image input from the decoder and output to the code decoder circuit 4 as an output 9A.

[0005] The code decoder circuit 4 restores one code input from the code data temporary storage circuit 3 using the position of the change point of the reference line, and sends out the restored run-length data to the image restoration circuit 6. . The image restoration circuit 6 restores the run-length data to image data and outputs it as an image data output 6A. The code decoder circuit 4
Is the length of the restored code, that is, code length data 1B
Is output.

On the other hand, the code data shift circuit 2 converts the 32-bit data received from the code data temporary storage circuit 3 into code length data 1B from the code decoder circuit 4.
And the processed code restored by the code decoder circuit 4 is discharged and removed. And
The 32-bit code data 2A is transferred to the code data combination circuit 1. The effective code data width storage circuit 7 adds the code length data (= 16) every time new code data 1A is taken into the code data combination circuit 1, and every time the code is restored by the code decoder circuit 4, the code length data (= 16) is added. Code length data 1B
Is subtracted to always know the width of the effective code data in the code data temporary storage circuit 3.

Therefore, when the width of the effective code data provided from the effective code data width storage circuit 7 becomes 16 bits or less, the code data combining circuit 1 fetches new 16 bits of code data 1A and stores the code data. It is connected immediately after valid code data among the code data obtained from the shift circuit 2. Conversely, if the width of the effective code data provided from the effective code data width storage circuit 7 is larger than the 16-bit width,
Without taking in the new 16-bit code data 1,
Move to the next cycle. According to this image decoding device, one code can be decoded in one clock (= 1 cycle).

[0008]

In recent years, a technique for reproducing an image having a gradation, such as a photograph, by using a technique for representing the density by the density of pixels in a pseudo manner has been established. Accompanying this, opportunities for processing images having a short run length are increasing.
In such an image, since the color of the image changes from white to black or from black to white in units of one pixel to several pixels, the run length is shortened, and the processing speed is reduced in the circuit of FIG. was there.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image decoding apparatus capable of eliminating the above-mentioned problems of the prior art and improving the processing speed of an image having a short run length.

[0010]

In order to achieve the above-mentioned object, the present invention relates to a decoding apparatus for coded data, comprising a first code decoding means for decoding only a predetermined short run-length code. And second decoding means for decoding all run-length codes, and when the first code of the code data to be decoded is the short run-length code, the processing within one cycle is performed. It is characterized in that the short run-length code and the code following it are decoded.

According to this feature, since the first code decoding means decodes only short run length codes, the types of codes to be decoded are small. As a result, the first code decoding means has a smaller circuit scale than the conventional code decoder circuit, and the time required for decoding becomes negligible as compared with the conventional code decoder circuit. Therefore, when used for decoding a short run-length image, the processing time is greatly reduced as compared with the conventional one, and the effect is great.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention. In the present embodiment, the newly input code data 1A is 16 bits for easy understanding, but the present invention is not limited to this.

In FIG. 1, reference numeral 10 denotes one of the main parts of the present invention, for example, a very small code decoder circuit for decoding only a code having a run length of "1", 11 a very small code data shift circuit, Reference numeral 12 denotes a code decoder circuit having the same scale as the conventional one, reference numeral 13 denotes an image restoration circuit, reference numeral 14 denotes a reference line change point detection circuit, reference numeral 15 denotes an addition circuit, and other reference numerals denote the same or equivalent components as those in FIG.

Next, the operation of this embodiment will be described in detail. As described with reference to FIG. 3, the code data combining circuit 1
When the effective code data width of the 32-bit code data from the code data shift circuit 2 becomes equal to or less than the 16-bit width, new 16-bit code data 1A is fetched and the code data obtained from the code data shift circuit 2 is read out. Combine immediately after valid code data. The combined code data is temporarily stored in the code data temporary storage circuit 3. Conversely, if the effective code data width of the 32-bit code data from the code data shift circuit 2 is larger than the 16-bit width, the code data combining circuit 1 converts the code data without taking in the new 16-bit code data 1A. Code data temporary storage circuit 3
Send to

If the code to be decoded next in the code data 4A stored in the code data temporary storage circuit 3 is a code of run length "1", the code decoder circuit 10 decodes the code and executes the code. The length data 5A is sent to the image restoration circuit 6. Further, the code length data 1B is sent to the code data shift circuit 11 and the addition circuit 15.
On the other hand, if the code in the code data 4A is not a code of run length "1", the code decoder circuit 10A
Does nothing.

When the code is decoded by the code decoder circuit 10, the code data shift circuit 11 shifts the input code data by the code length data 1B and sends it to the code decoder circuit 12. The code decoder circuit 12 operates similarly to the conventional code decoder circuit 4 (see FIG. 3).
Decode the input code. Then, the run length data 10A is sent to the image restoration circuit 13. The image restoration circuit 13 restores the run-length data 10A to image data in the same manner as the conventional image restoration circuit. The restored image data is sent to a subsequent circuit (not shown).

On the other hand, when the code to be decoded is not the code of run length "1" and the code decoder circuit 10 does not operate, the code data shift circuit 11 outputs the code data without any shift. , Bypass the shift process.

The code data shifted or not shifted by the code data shift circuit 11 is sent to the code decoder circuit 12 and also sent to the code data shift circuit 2. The code data shift circuit 2 shifts the received code data by the data length indicated by the code length data 3B output from the code decoder circuit 12, and sends it to the code data combining circuit 1.

On the other hand, the code decoder circuits 10 and 1
Code length data 1 which is the length of the code decoded in 2
B and 3B are added by the addition circuit 15 and sent to the effective code data width storage circuit 7. Effective code data width storage circuit 7
Adds the code length data (= 16) every time new code data 1A is taken into the code data combination circuit 1, and every time the code is restored by the code decoder circuits 10 and 12, the addition circuit 15 The output code length data (1B
By subtracting (+ 3B), the effective code data width of the code data temporary storage circuit 3 is always known.

Therefore, the code data combination circuit 1 determines whether or not to take in new code data 1A based on the effective code data width information 2B provided from the effective code data width storage circuit 7. Thus, one cycle of the decoding operation is completed.

As is clear from the above description, the code decoder circuit 10 of the present embodiment decodes only the code of run length "1". Since there are few types of codes of run length "1", the circuit scale is slightly smaller than that of a conventional code decoder circuit, for example, the code decoder circuit 4 of FIG. Also, the time required for decoding is negligible compared to the conventional code decoder circuit.

The code data shift circuit 11 shifts the code data based on the code length output from the code decoder circuit 10. As described above, the types of codes decoded by the code decoder circuit 10 are small. In addition, since the code length is short, it is possible to configure the circuit with a small-scale circuit, and the time required for the shift processing is negligible as compared with the conventional one.

Therefore, according to the present embodiment, the code of the run-length "1" and the next code following the code "1" are decoded in substantially the same time as one cycle required for the conventional decoding. Will be able to As described above, in recent years, a technique for reproducing an image having a gradation such as a photograph using a technique for representing density in a pseudo manner by the density of pixels has been established, and the color of an image has been reduced from one pixel to several pixels. The chances of processing short run-length images such as changing from white to black, or from black to white are increasing, but when the decoding device of the present embodiment is used to decode code data of such images, The effect is very large.

In the above-described embodiment, the code decoder circuit 10 decodes only the code of run length "1", but the present invention is not limited to this.
Decoding only the respective codes such as run lengths "2" and "3", or, for example, run lengths "1" to "3"
May be decoded. In short,
What is necessary is just to make the code decoder circuit 10 decode only a small number of codes.

As shown in FIG. 2, the code decoder circuit 10 is provided with a code decoder circuit 10 'for decoding, for example, only a code having a run length of "2", and a code having a run length of "1". Is a code decoder circuit 10
And the code of run length "2" is the code decoder circuit 10
′, And other run-length codes may be decoded by the code decoder circuit 12.

In FIG. 2, for example, a code decoder circuit 1 for decoding a plurality of, for example, three types of short codes is provided.
., May be provided in parallel, and decoding of the plurality of short codes and decoding of normal codes by the code decoder circuit 12 (see FIG. 1) may be performed in one clock. In this way, for example, four codes can be decoded with one clock. Note that this can also be realized by giving the code decoder circuit 10 of FIG. 1 a function of decoding a plurality of types of short codes.

[0027]

As is apparent from the above description, according to the present invention, a code having a short run length is made by the first code decoding means for high-speed processing, and a code following the code is made by the second code decoding means. Therefore, one of the conventional decoding devices
In the cycle time, one or more short run-length codes and the following or subsequent codes can be decoded. In recent years, there has been an increasing number of opportunities to process short run-length images in which the color of an image changes from white to black or from black to white in units of one pixel to several pixels. When the decoding device of the present invention is used for decoding, the effect becomes very large.

[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 block diagram of a main part of a modified example of the present invention.

FIG. 3 is a block diagram illustrating a configuration of an example of a conventional device.

[Explanation of symbols]

1 code data combining circuit, 2, 11 code data shift circuit, 3, 12 code data temporary storage circuit, 4, 10,
12: code decoder circuit, 5, 14: reference line change point detection circuit, 6, 13: image restoration circuit, 7: effective code data width storage circuit, 15: addition circuit.

Claims (9)

[Claims] 1. An apparatus for decoding encoded data, comprising: first code decoding means for decoding only a predetermined short run-length code; and second decoding means for decoding all run-length codes. When the leading code of the code data to be decoded is the short run-length code, the short run-length code and the code following it are decoded in one cycle. An image decoding device, characterized in that: 2. The image decoding apparatus according to claim 1, wherein said first code decoding means decodes one or a plurality of predetermined short run-length codes. Image decoding device. 3. The image decoding device according to claim 1, wherein said first code decoding means and said second decoding means are connected in series, and said second decoding means is provided with said first decoding means. An image decoding apparatus, wherein code data shifted by a code length decoded by a code decoding means is input. 4. The image decoding apparatus according to claim 1, wherein the first and second decoding units are configured to generate a reference image obtained from image data of a reference line and position data of a restored image. An image decoding apparatus for decoding an input code using a position of a line change point. 5. The image decoding apparatus according to claim 1, wherein said first code decoding means connects a plurality of code decoding means for decoding only different short run-length codes in parallel. An image decoding device, characterized in that: 6. The image decoding apparatus according to claim 1, wherein the code lengths decoded by said first and second decoding means are added to each other, and the validity of code data not yet decoded is added. An image decoding device wherein a code data width is obtained. 7. The image decoding apparatus according to claim 6, wherein code data that has not been decoded is shifted by a code length decoded by said second code decoding means, and said effective code data width is set to a predetermined value. An image decoding apparatus, wherein when the size is equal to or less than the size, new code data is combined immediately after the valid data of the shifted code data. 8. The image decoding device according to claim 1, wherein the image decoding device is a binary code decoding device in which a change point between a run length and a reference line is entropy-encoded and compressed. An image decoding device, comprising: 9. The image decoding apparatus according to claim 1, wherein a plurality of short codes and a code subsequent thereto are decoded in the same cycle time. Decoding device.