JP3123797B2 - Coding device and decoding device for predictive coding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an encoding apparatus and a decoding apparatus of a predictive coding system for predicting a target pixel based on the state of surrounding pixels and coding image information based on the result of the prediction.

[0002]

2. Description of the Related Art There is known a predictive coding method in which each pixel of image information is predicted based on the state of surrounding pixels indicated by a template, and image information is encoded or decoded based on the result of the prediction.

[0003] The above-mentioned template indicates the position of each peripheral pixel located at a certain position with respect to the target pixel. It is well known that when image information is encoded by a predictive encoding method, a high data compression ratio can be obtained by setting a template according to the properties of an image.

FIG. 5A shows an example of a template. A hatched frame indicates a target pixel, and a blank frame indicates peripheral pixels to be referred to. In the case of a binary image such as a character or a graphic, a high data compression ratio can be obtained by arranging surrounding pixels to be referenced near the target pixel as shown in FIG. On the other hand, in the case of a pseudo halftone image such as a picture or a photograph, a high data compression rate can be obtained by arranging surrounding pixels to be referred to in a relatively wide range as shown in FIG.

When transmitting image information as in a facsimile apparatus, it is necessary to use the same template for encoding on the transmitting side and decoding on the receiving side.

[0006] However, in such a case, the transmitting side has 2
The value image and the halftone image are arbitrarily transmitted without distinction. Also,
An image in which these two types of images are mixed in one page may be transmitted.

Conventionally, to cope with such transmission,
In the case where a binary image is transmitted or a halftone image is transmitted, a somewhat high data compression ratio can be obtained as shown in FIG.
The template shown in Fig. 1 was used in a fixed manner.

[0008]

Therefore, conventionally, there has been a problem that various image information cannot always be efficiently encoded and decoded at a high data compression rate.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide an encoding apparatus and a decoding apparatus of a predictive encoding system capable of always efficiently encoding and decoding various images.

[0010]

For this purpose, the encoding apparatus according to the present invention is arranged such that each time one pixel of image information is input, the pixel coincides with each pixel in a certain range which is determined in advance as a floating pixel candidate. The number of times is counted for each pixel of the floating pixel candidate, and each time a fixed amount of image information is input, each count value is determined, and if a certain condition is satisfied, a certain number of pixels having a large count value are floated. The position of the selected floating pixel, which is selected as a pixel, and the positions of a plurality of fixed pixels fixedly set in advance are set in the template.

The decoding apparatus according to the present invention executes the same processing as described above on the basis of image information restored one pixel at a time from encoded image information.

[0012]

According to the image information being processed, a pixel position having a strong correlation with the pixel of interest is set in the template, and the prediction accuracy is improved. Therefore, various images are always efficiently encoded and decoded at a high data compression ratio. Will be able to

[0013]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a transmitting side of an image transmitting apparatus according to an embodiment of the present invention. In the figure, a template pixel extracting unit 1 and a template setting unit 2
, Image information of a target pixel and surrounding pixels is input from an external device (not shown). The target pixel is each pixel of the binary image information to be encoded, and the surrounding pixels are a plurality of peripheral pixels located within a certain range with respect to the target pixel.

The template pixel extracting section 1 extracts each pixel at a predetermined position from the inputted surrounding pixels. The template setting unit 2 sets a pixel position to be extracted by the template pixel extraction unit 1. The encoding unit 3 encodes the image information according to a known predictive encoding method, and the transmission unit 4 transmits the encoded image information.

In the template setting section 2, a coincidence number counting section 21 counts the number of coincidences between a plurality of pixels set as floating pixel candidates among surrounding pixels and a target pixel. The maximum pixel position determining unit 22 determines a pixel position at which the count value indicates the maximum value. The floating pixel position storage unit 23 stores the position of one selected floating pixel. The maximum pixel position storage unit 25 stores a pixel position at which the count value indicates the maximum value. The continuous number counting section 26 counts the number of times that the count value at the same pixel position continuously shows the maximum value.

FIG. 2 shows the receiving side of the image transmission apparatus of the present embodiment. In the figure, a receiving unit 5 receives encoded image information to be transmitted, and a decoding unit 6 decodes the encoded image information into original image information. The decoded image information is output to the outside, and surrounding pixels having the image information as a target pixel are input from the outside. The template pixel extraction unit 1 and the template setting unit 2
The same operation as that on the transmission side is performed on the target pixel and surrounding pixels.

With the above configuration, assuming that the operation of the image transmission apparatus of this embodiment has just started, the transmission side sequentially inputs image information to be transmitted and image information of surrounding pixels from an external device (not shown). Is done. The template pixel extracting unit 1 extracts each pixel at a predetermined position from the input surrounding pixels and outputs the extracted pixel together with the target pixel. The encoding unit 3 predicts a target pixel based on each of the extracted pixels, and sequentially codes the target pixel based on the result of matching or mismatch between the prediction result and the actual target pixel. The transmitting unit 4 sequentially transmits the encoded image information.

During this operation, the template setting section 2 periodically sets the pixel position to be extracted in the template pixel extracting section 1. In this case, the pixel position 1 to be extracted is, as shown in FIG.
And a floating pixel candidate position C are set. The fixed pixel position B is nine pixels that are always fixedly extracted. The floating pixel candidate position C is set to 10 in this range according to the content of the image information.
One of the pixels is selected as the floating pixel position.

When the operation of the image transmission apparatus is started, the template setting section 2 first selects one of the floating pixel candidate positions C as a temporary floating pixel position as shown in FIG. And the position is stored in the floating pixel position storage unit 23 (process 10).
1). Also, the number-of-matches counting section 21 and the continuous number counting section 26 are reset (steps 102 and 103). Thereafter, the image information is sequentially input, and the template pixel extracting unit 1, the encoding unit 3, and the transmitting unit 4 execute the above operation.

During the operation, the template setting section 2 checks whether or not the specified number of pixels have been input each time one pixel of interest is input (Step 104) (Step 10).
5). The number of pixels is fixedly set in advance in pixel units or line units. If the specified number of pixels has not been input (N in processing 105), the number of matches between the target pixel and each pixel of the floating pixel candidate is counted by the matching number counting section 21 (processing 106), and the number of input pixels is calculated. The check is repeated (to process 104). Thus, ten types of counting operations corresponding to the ten floating pixel candidates are performed.

When the above operation for the specified number of pixels is completed (Y in process 105), the count value a indicating the maximum value among the 10 types of count values corresponding to the floating pixel candidates is determined (process 107). . Then, the count value b corresponding to the set floating pixel is read (process 108) and compared with the count value a (process 109).

A pixel having a large count value has a strong correlation with a pixel of interest. It is well known that, when encoding is performed by the predictive encoding method of image information, extracting each pixel having a strong correlation with the pixel of interest improves prediction accuracy and improves a data compression ratio of image information.

Therefore, in this embodiment, the count values a, b
If the ratio a / b exceeds the specified value (step 10
9) Y, one of the floating pixel candidates having the maximum count value is selected as a floating pixel, set in the template pixel extracting unit 1, and the floating pixel position storage unit 23 stores the position of the floating pixel. (Process 110).

If the ratio a / b of the count values a and b is less than the specified value (N in step 111), the pixel position that has now shown the maximum value and the pixel position that has shown the previous maximum position are the same. Is determined (step 111). Now, the first
If the operation is the first operation, since the previous maximum pixel position is not stored, this determination is not the same. In this case (N in Step 111), the maximum pixel position at this time is stored in the maximum pixel position storage unit 25 (Step 112). Thereafter, the same processing is repeated from the processing 102.

Here, it is assumed that the pixel position indicating the maximum value becomes the same as the pixel position indicating the previous maximum position when the above operation for the specified number of pixels is completed next. In this case (Y in process 111), the number of continuous times is counted by the continuous number counting unit 26 (process 113). Then, the count value is compared with a preset specified value (step 114). Now, if the count value is smaller than the specified value (N in step 114), the above processing is repeated from step 103.

Assuming that the pixel position showing the maximum value has not changed, the count value increases. If the count value exceeds the above-mentioned specification (Y in step 114),
The pixel is set as a floating pixel (step 110), and the same processing is performed.

By the operation of the template setting unit 2 as described above, the extraction pixel position corresponding to the image information is set in the template pixel extraction unit 1. Thereby, the encoded image information is transmitted.

On the receiving side, the receiving unit 5 receives the transmitted image information. The decoding unit 6 predicts a target pixel based on the image information extracted by the template pixel extraction unit 1, and decodes the received coded image information into the original image information based on the prediction result. The decoded image information is output to an external device, and image information of surrounding pixels is input from the external device. The image information of the surrounding pixels is image information of each pixel at the fixed pixel position B and the floating pixel candidate position C shown in FIG.

The template setting section 2 similarly executes the processing described with reference to FIG. 4 based on the inputted surrounding pixels and the target pixel which is the decoded image information. As a result, during the reception of the image information and the execution of the decoding operation, the extraction pixel position corresponding to the image information is set in the template pixel extraction unit 1.

The template pixel extracting unit 1 extracts each pixel at a set pixel position from surrounding pixels and outputs the extracted pixel to the decoding unit 6. The decoding unit 6 executes the above-described decoding processing based on the extracted pixels.

As described above, in the present embodiment, the template pixel extracting unit 1 extracts a plurality of fixed pixels whose positions are always fixed and one floating pixel whose position moves, from among the surrounding pixels. I have to. Then, at the time of encoding and decoding processing, every time the image information is processed by a certain number of pixels, the number of coincidences between the pixel of interest and each pixel of the floating pixel candidate is counted, and the pixel having the maximum count value, that is, Pixels having a strong correlation are set as floating pixels.

Thus, the template pixel extracting unit 1
Can extract surrounding pixels having a strong correlation with the pixel of interest in the image information being processed. Therefore, whether the image to be processed is a binary image, a halftone image, or an image in which both are mixed, it is possible to always encode the image information at a high data compression rate and execute efficient encoding / decoding processing. become able to.

In the above embodiment, since the floating pixel is set to one pixel, the floating pixel can be selected by the relatively simple judgment processing described with reference to FIG. However, a plurality of floating pixels may be selected according to the image information, in which case the data compression ratio can be further improved.

In the above embodiment, the case where coded image information is transmitted has been described as an example. However, for example, when image information is stored in a storage device by an image filing device, image data is encoded by a predictive coding method. The present invention can be similarly applied to various devices for compressing information.

[0036]

As described above, according to the present invention, each time one pixel of image information to be encoded is input, or each time one pixel of original image information is restored from the encoded image information, the pixel is floated. By counting the number of matches with each pixel determined as a pixel candidate, a floating pixel having a strong correlation with the target pixel is selected and set in the template, so that the prediction accuracy is improved, and various images are constantly improved. Encoding and decoding can be efficiently performed at the data compression ratio.

[Brief description of the drawings]

FIG. 1 is a block diagram of a transmission side of an image transmission apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram of a receiving side of the image transmission apparatus.

FIG. 3 is an explanatory diagram of a template indicating pixel positions to be extracted.

FIG. 4 is an operation flowchart of a template setting unit.

FIG. 5 is an explanatory diagram of various conventional templates.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 template pixel extracting unit 2 template setting unit 3 encoding unit 4 transmitting unit 5 receiving unit 6 decoding unit 21 matching number counting unit 22 maximum pixel position determining unit 23 floating pixel position storage unit 25 maximum pixel position storage unit 26 continuous count Department

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04N 1/41-1/419 H03M 7/30 G06T 9/00

Claims (4)

(57) [Claims] An image processing apparatus includes a template that indicates the position of each pixel around a pixel of interest, inputs image information one pixel at a time, and predicts a pixel of interest based on the state of each pixel indicated by the template. In the coding apparatus of the predictive coding method for generating a code, each time one pixel of the image information is input, the number of matches between the pixel and each pixel at a predetermined position previously determined as a floating pixel candidate is determined by the floating pixel Matching number counting means for counting for each pixel of the candidate,
A floating pixel selecting unit that determines a count value for each pixel every time the image information is input and determines a fixed number of pixels having a large count value as a floating pixel when a predetermined condition is satisfied, A coding device for a predictive coding method, comprising: template setting means for setting the position of the selected floating pixel and the positions of a plurality of fixed pixels fixedly set in advance in the template. . 2. The floating pixel selecting means is means for selecting one floating pixel, means for storing the position of the selected floating pixel and the count value, and newly selecting the floating pixel. When the pixel value of the floating pixel candidate whose count value indicates the new maximum value is different from the stored old floating pixel position, the old count value stored by the new count value Means for selecting, as a new floating pixel, one pixel of the floating pixel candidate which newly shows the maximum value when the value is larger by a certain multiple of the value, and the floating pixel whose count value shows the new maximum value When the pixel position of the candidate matches the stored old floating pixel position, one of the floating pixel candidates showing the maximum value when the matching state is repeated a certain number of times.
2. A coding apparatus according to claim 1, further comprising means for selecting a pixel as the new floating pixel. 3. A template that indicates the position of each pixel around the target pixel is provided. The target pixel is predicted based on the state of each pixel indicated by the template in the image information to be restored one pixel at a time, and based on the prediction result. In a decoding apparatus of a predictive coding method for restoring input coded image information to original image information one pixel at a time, each time the image information is restored one pixel, the pixel and the floating pixel candidate are determined in advance. A coincidence count means for counting the number of coincidences with each pixel at a fixed position for each pixel of the floating pixel candidate, and each time the image information is restored to a fixed number of pixels, the count value for each pixel is determined and fixed. A floating pixel selecting means for selecting a fixed number of pixels having a large count value as a floating pixel when the condition is satisfied; and a plurality of fixed pixels fixedly set to the position of the selected floating pixel. And a template setting means for setting the position of the template in the template. 4. The floating pixel selecting means is means for selecting one floating pixel, storing the position of the selected floating pixel and the count value, and newly selecting the floating pixel. When the pixel value of the floating pixel candidate in which the count value newly indicates the maximum value is different from the stored old floating pixel position, the old count in which the new count value is stored Means for selecting, as a new floating pixel, one pixel of the floating pixel candidate that newly shows a maximum value when the count value is larger by a certain multiple of the count value; When the pixel position of the pixel candidate matches the stored old floating pixel position, one of the floating pixel candidates having the maximum value when the matching state is repeated a predetermined number of times.
4. The decoding apparatus according to claim 3, further comprising means for selecting a pixel as the new floating pixel.