JPH09200542A - Predictive coding device, decoding device, predictive coding method and picture processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve coding efficiency by changing a prediction system by the property of pictures. SOLUTION: Picture data 1 are inputted to an adaptive prediction position selection processing part 2 and simultaneously inputted to a picture property detection part 8. In the adaptive prediction position selection processing part 2, the position of a reference picture element to a picture element under consideration, that is an adaptive prediction position, is selected corresponding to the detected result of the picture property detection part 8 and a predicted value 4 is outputted. The predicted value 4 is inputted to a prediction processing part 3 and prediction error data 5 which are the difference of the value of the picture element P under consideration and the predicted value are outputted. By a coding part 6, the prediction error data 5 are coded to code data 7 of RL codes or the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image data predictive coding apparatus, a decoding apparatus, a predictive coding method, and an image processing apparatus.

[0002]

2. Description of the Related Art As one of image coding techniques, there is known a predictive coding technique for predicting a target pixel level from peripheral pixel levels and coding prediction error data. In this technique, it is necessary to improve the predictive predictive value in order to increase the coding efficiency.

JP-A-5-316370 and JP-B-6
In the encoding technique described in Japanese Patent Laid-Open No. 3-9426, a predictor having a high hit rate is adaptively switched from among a plurality of predictors, and finally one predictor is selected to determine the value of the value of the current image. Used for prediction to generate prediction error data.

Further, in the encoding method and the decoding method described in Japanese Patent Publication No. 6-95645, prediction is performed by using the predicted values output by the table lookup method with the values of a plurality of peripheral pixels as addresses. Although the error data is generated, the positions of the predicted pixels are not all fixed, but the position of only one pixel can be made variable, and the predicted position is changed according to the predictive hit ratio.

As described above, in the conventional technique, the predictor is adaptively switched based on the prediction result to improve the prediction efficiency.

However, in these conventional techniques, although the reference position of the prediction pixel is adaptively changed, the characteristics of the image to be compressed are not taken into consideration, and therefore the same prediction method is applied to any image. To use. Therefore, there is a problem that the prediction efficiency is low. In addition, special fair 6
As disclosed in Japanese Patent Publication No. 95645, in the method of writing the predicted value in the memory, when the number of reference pixels is increased, the memory capacity is increased and the read time is increased, and the coding speed is decreased. There is.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and a predictive coding apparatus capable of improving the coding efficiency by changing the prediction method depending on the nature of the image. It is an object of the present invention to provide a decoding device, a predictive coding method, and an image processing device.

[0008]

According to a first aspect of the present invention, in a predictive coding apparatus, a detecting means for detecting a characteristic based on an image and a position of a reference pixel are selected based on an output of the detecting means. Reference pixel selecting means, predicting means for predicting the value of the target pixel based on the value of the reference pixel selected by the reference pixel selecting means, and encoding means for performing encoding based on the prediction result by the predicting means. It is characterized by having.

According to a second aspect of the present invention, in the predictive coding device, a plurality of predicting means for predicting a value of the target pixel from a plurality of pixels located around the target pixel, and detection for detecting a characteristic based on the image. Means, selecting means for selecting the predicting means based on the output of the detecting means, and coding means for performing coding based on the prediction result by the predicting means selected by the selecting means. To do.

According to a third aspect of the present invention, in the predictive coding apparatus according to the first or second aspect, the detecting means is
The feature is that the property of the dither image is detected as the characteristic based on the image.

According to a fourth aspect of the present invention, in the predictive coding apparatus according to the first or second aspect, the detecting means is
It is characterized in that the code amount output from the encoding means is detected as the characteristic based on the image.

According to a fifth aspect of the present invention, in the predictive coding apparatus according to the first aspect, the reference pixel selection means is
It is characterized in that the position of the reference pixel is determined for each predetermined line.

According to a sixth aspect of the present invention, in the predictive coding apparatus according to the second aspect, the selecting means selects the predicting means for each predetermined line.

According to a seventh aspect of the present invention, in a decoding device, the code data encoded by the predictive encoding device according to any one of the first to sixth aspects is decoded to generate prediction error data. Decoding means, detecting means for detecting a characteristic based on the original image, reference pixel selecting means for selecting a position of a reference pixel based on the characteristic detected by the detecting means,
It is characterized by comprising an inverse prediction means for performing an inverse prediction process from the prediction error data based on the value of the reference pixel selected by the reference pixel selection means to restore the original image.

According to an eighth aspect of the present invention, in a decoding device, the coded data encoded by the predictive encoding device according to any one of the first to sixth aspects is decoded to generate prediction error data. Decoding means, a plurality of inverse prediction means for performing an inverse prediction process from the prediction error data to restore an original image, a detection means for detecting a characteristic based on the original image,
Selecting means for selecting the inverse predicting means based on the characteristics detected by the detecting means, and performing inverse prediction processing from the prediction error data by the inverse predicting means selected by the selecting means to restore the original image. It is a feature.

According to a ninth aspect of the present invention, in the decoding device according to the seventh or eighth aspect, the detecting means detects the code amount input to the decoding means as a characteristic based on the original image. It is what

According to a tenth aspect of the present invention, in the decoding device according to the seventh aspect, the reference pixel selection means determines the position of the reference pixel for each predetermined line.

The eleventh aspect of the present invention is the decoding apparatus according to the eighth aspect, wherein the selecting means selects the inverse predicting means for each predetermined line.

According to the twelfth aspect of the present invention, in the predictive coding method, the characteristic based on the image is detected, the position of the reference pixel is selected based on the detection result, and the target is selected based on the value of the selected reference pixel. It is characterized in that the value of a pixel is predicted and the encoding is performed based on the prediction result.

According to a thirteenth aspect of the present invention, in the predictive coding method according to the twelfth aspect, whether or not the image is a dither image is detected as a characteristic based on the image.

According to a fourteenth aspect of the present invention, in the predictive encoding method according to the twelfth aspect, the code amount after encoding is detected as a characteristic based on an image.

According to a fifteenth aspect of the invention, in the predictive coding method according to the twelfth aspect, the position of the reference pixel is selected for each predetermined line.

According to a sixteenth aspect of the present invention, in the image processing apparatus, the predictive coding apparatus according to any one of the first to sixth aspects and the decoding apparatus according to any one of the seven to eleventh aspects are provided. It is characterized by having.

[0024]

1 is a block diagram showing a first embodiment of an encoding apparatus of the present invention. In the figure, 1 is image data, 2 is an adaptive prediction position selection processing unit, 3 is a prediction processing unit, 4 is a prediction value, 5 is prediction error data, 6 is an encoding unit,
Reference numeral 7 is code data, 8 is an image property detection unit, and 9 is a selection signal.

The image data 1 is input to the adaptive predicted position selection processing unit 2 and at the same time, is input to the image property detection unit 8. In the adaptive predicted position selection processing unit 2, the position of the reference pixel with respect to the target pixel, that is, the adaptive predicted position is selected according to the detection result of the image property detection unit 8 and the predicted value 4 is output.

The prediction value selection process will be described. FIG.
(A) illustrates positions X _{9 to} X ₀ up to 10 pixels before the pixel of interest P in the row direction and positions Y _{2 to} Y ₀ of 3 pixels including before and after the pixel of interest on one line. ing. As the predicted position of the target pixel P from the pixels at the total 13 positions,
It is considered that the position that seems to have the highest predictive predictive value is adaptively selected and the value of the pixel is set to the predicted value 4. Of course, the number of pixels is not limited to 13 in FIG.
The number of pixels in the row direction may be increased, or the number of rows above may be increased.

The position to be used for prediction is selected from the target pixels whose range is determined in this way.
In the prediction method described in Japanese Patent No. 16370, positions to be finally used for prediction are determined from these prediction target positions from several pixels before.

However, for example, when the image property is a dither image binarized by an 8 × 8 dither matrix, the pixel at the position of X ₇ which is 8 pixels before the pixel of interest P. The data has a strong correlation, and X _{1 to} X ₆ 2 to 7 pixels before
It is considered that the correlation with the image data at the position is weak. However, in the prediction method described in Japanese Patent Laid-Open No. 5-316370, the position 8 pixels before is not recognized as a special position.
The position before the pixel may be selected, and in that case, misprediction is likely to occur.

In the present invention, in the image property detecting section 8,
If it is determined that the image is an 8 × 8 dither image, the selection signal 9
From the pixel reference position in FIG. 2A, X _{1 to} X ₆ ,
Remove the _{X 8, X 9, Y 1} , Y 2, stop in a position of _{X 7, X 0, Y 0} , and to select the final predicted position adaptive prediction to from this. FIG. 2B shows the positions of pixels in the prediction selection range in the case of an 8 × 8 dither image.

Further, in the screen image and the like after the error diffusion processing, it is considered that the pixels around the target pixel P have stronger correlation. Therefore, the position of the pixel in the prediction selection range is Y ₀
It is narrowed down to the positions of Y ₂ and X ₀ .

The value of the pixel at the position determined as described above, that is, the value of the pixel at the final predicted position becomes the predicted value 4 and is input to the prediction processing unit 3. The prediction processing unit 3 outputs the prediction error data 7 which is the difference between the value of the pixel of interest P and the prediction value, and the coding unit 6 codes the prediction error data 5 into code data 7 such as an RL code. It

The image property detecting section 8 will be described. In this embodiment, the image property detection unit 8 detects whether or not the image is a dither image. Of course, the image property detecting unit 8 may analyze the image data 1 to detect whether or not it is a dither image. In this case, if the dither image data has a unit matrix of 8 × 8, then 8 × 8
Since the periodicity of each pixel is seen, it can be detected that the image is a dither image. Therefore, the dither image can be detected by detecting the presence or absence of periodicity based on the unit matrix.

Further, the image data 1 is generally binarized from the grayscale data of the analog signal. When the dither image data is used for binarization, the information indicating that the image is a dither image and the unit matrix size information are added to the image data 1. The image property detection unit 8 may detect this information. Whether or not the image is a dither image can be detected based on whether or not this information is detected.

FIG. 3 is a block diagram showing a second embodiment of the coding apparatus of the present invention. In the figure, the same parts as those in FIG. Reference numeral 11 is a code amount count control unit. In this embodiment, it is assumed that the dither image is an 8 × 8 unit matrix. Therefore, the adaptive predicted position selection processing unit 2
In order to use the predicted position for the 8 × 8 dither matrix described in FIG.
Predicted position selection processing is performed.

Code data 7 generated by this processing
Is input to the code amount count control unit 11 and the code amount is counted. The counted code amount for each line or several lines is compared with a predetermined threshold value, and when the code amount is larger than the threshold value, it is determined that the currently input image is not a dither image. The determination result is supplied to the adaptive predicted position selection processing unit 2 as the selection signal 9, and when it is not the dither image, the adaptive predicted position selection processing unit uses the predicted position for the screen image described in FIG. 2C. 2 is switched.

In the above description, the adaptive predictive position selection processing unit 2 is set so that the predictive positions for the 8 × 8 dither matrix are used first, but the predictive positions for the unit matrices of various sizes are set. As used, the code amount of the code data of the predetermined number of lines in each case may be sequentially switched to be compared with the threshold value. In this case, the code amount of the code data may be compared when the predicted position for the screen image is used. Instead of comparing with the threshold value, mutual comparison may be performed.

FIG. 4 is a block diagram showing a third embodiment of the coding apparatus of the present invention. In the figure, the same parts as those in FIGS. 1 and 2 are denoted by the same reference numerals, and description thereof will be omitted. Reference numeral 12 is a selector, and 13 is a memory type prediction unit. In this embodiment, the memory type prediction unit 1 is different from the second embodiment.
3 is added, and the predictive value 4 output from the adaptive predictive position selection processing unit 2 and the predictive value 4 output from the memory type predicting unit 13 are switched by the selector 12.

Description will be made with reference to FIG. The reference position of the adaptive predicted position selection processing unit 2 is configured only in the horizontal direction, as shown in FIG. In addition, the memory type prediction unit 13
As shown in FIG. 5B, the previous pixel X ₀ of the target pixel P,
It is composed of X _{1 to} X ₃ in the previous line. Memory type prediction unit 13
, X _{0 to} X _{3 as} shown in the table of FIG.
The predicted value corresponding to the value of is stored in the memory in advance, and the predicted value is output according to the input values of X _{0 to} X ₃ . This memory type prediction unit 13
The prediction table may be set with a predicted value in advance, or may be rewritable during the process.

It is assumed that the selector 12 has previously selected the prediction value 4 from the adaptive predictor processing unit 2. The code data 7 generated by this processing is input to the code amount count control unit 11 and the code amount is counted. At the same time, the code amount is compared with a certain threshold value for every one line or every several lines, and when the code amount is large, the selector 12 is controlled by the selection signal 9 to obtain the prediction value 4 output from the memory type prediction unit 13. Can be switched.

As a modification of this embodiment, although not shown, the prediction unit may be composed of only a memory type prediction unit, and the position of the reference pixel may be changed by the selection signal 9.

Although the encoding process according to the present invention has been described above, the decoding process can be configured in substantially the same manner.

FIG. 6 is a block diagram showing an embodiment of the decoding apparatus of the present invention. In the figure, 1 is image data, 4 is a prediction value, 5 is prediction error data, 7 is code data, 9 is a selection signal, 11 is a code amount count control unit, 21 is an adaptive inverse prediction position selection processing unit, and 22 is inverse. The prediction processing unit 23 is a decoding unit.

The code data 7 is the code amount count controller 1
1, and at the same time, is input to the decoding unit 23. In the decoding unit 23, the code data 7 is the prediction error data 5
And is input to the inverse prediction processing unit 22 together with the prediction value 4 selected by the adaptive inverse prediction position selection processing unit 21,
Converted to image data 1.

At this time, the adaptive inverse prediction position selection processing unit 21
In the same manner as in encoding, the code amount count control unit 1
The position of a pixel used for prediction and the like are determined by the selection signal 9 output from 1.

The above-described decoding process corresponds to the encoding described with reference to FIGS. 1 and 3, but the decoding of the encoding described with reference to FIG. 4 is performed by performing the inverse prediction corresponding to the memory type prediction unit. Can be similarly configured.

An image processing apparatus can be constructed using the encoding apparatus and the decoding apparatus according to the present invention. The encoding apparatus can increase the data compression rate, which is advantageous when storing or transferring image data. The data read from the memory or transferred is
The decoding device can decode the image data with good reproducibility.

[0047]

As is apparent from the above description, according to the present invention, it is possible to switch the pixel position used for prediction or the prediction method in accordance with the property of image data. There is an advantage that the encoding speed can be improved and the encoding efficiency can be improved with the scale reduction and the scale reduction of the predictor. There is an effect that the encoded code data can be decoded with good reproducibility.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of an encoding device of the present invention.

FIG. 2 is an explanatory diagram of positions of reference pixels in the first embodiment of the encoding device of the present invention.

FIG. 3 is a block diagram showing a second embodiment of an encoding device of the present invention.

FIG. 4 is a block diagram showing a third embodiment of the encoding device of the present invention.

FIG. 5 is an explanatory diagram of reference pixels in the third embodiment of the encoding device of the present invention.

FIG. 6 is a block diagram showing an embodiment of a decoding device of the present invention.

[Explanation of symbols]

1 ... Image data, 2 ... Adaptive prediction position selection processing unit, 3 ... Prediction processing unit, 4 ... Prediction value, 5 ... Prediction error data, 6 ... Encoding unit, 7 ... Code data, 8 ... Image property detection unit, 9 ... selection signal, 11 ... code amount count control unit, 12 ... selector,
13 ... Memory type prediction unit, 21 ... Adaptive inverse prediction position selection processing unit, 22 ... Inverse prediction processing unit, 23 ... Decoding unit.

Claims (16)

[Claims] 1. A detection means for detecting a characteristic based on an image, a reference pixel selection means for selecting a position of a reference pixel based on an output of the detection means, and a value of the reference pixel selected by the reference pixel selection means. A predictive coding apparatus comprising: a prediction unit that predicts a value of a target pixel based on the above; and a coding unit that performs coding based on a prediction result by the prediction unit. 2. A plurality of prediction means for predicting a value of a target pixel from a plurality of pixels located around the target pixel, a detection means for detecting a characteristic based on an image, and the prediction based on an output of the detection means. A predictive coding apparatus comprising: a selecting unit that selects a unit, and a coding unit that performs coding based on a prediction result by the predicting unit selected by the selecting unit. 3. The predictive coding apparatus according to claim 1, wherein the detecting unit detects a property of the dither image as a characteristic based on the image. 4. The predictive coding apparatus according to claim 1, wherein the detection unit detects a code amount output from the coding unit as a characteristic based on an image. 5. The predictive coding apparatus according to claim 1, wherein the reference pixel selection means determines the position of the reference pixel for each predetermined line. 6. The predictive coding apparatus according to claim 2, wherein the selection means selects the prediction means for each predetermined line. 7. Decoding means for decoding coded data coded by the predictive coding apparatus according to claim 1 to generate prediction error data, and detecting characteristics based on an original image. Detecting means, a reference pixel selecting means for selecting the position of the reference pixel based on the characteristic detected by the detecting means, and an inverse of the prediction error data based on the value of the reference pixel selected by the reference pixel selecting means. A decoding device comprising an inverse prediction unit that performs a prediction process to restore an original image. 8. Decoding means for decoding coded data coded by the predictive coding apparatus according to claim 1 to generate prediction error data, and inverse prediction from the prediction error data. A plurality of inverse prediction means for performing processing to restore the original image; a detection means for detecting a characteristic based on the original image; a selection means for selecting the inverse prediction means based on the characteristic detected by the detection means; A decoding device characterized in that the inverse prediction means selected by the selection means performs inverse prediction processing from the prediction error data to restore an original image. 9. The decoding apparatus according to claim 7, wherein the detection unit detects the code amount input to the decoding unit as a characteristic based on the original image. 10. The decoding device according to claim 7, wherein the reference pixel selection means determines the position of the reference pixel for each predetermined line. 11. The decoding device according to claim 8, wherein the selection unit selects the inverse prediction unit for each predetermined line. 12. A characteristic based on an image is detected, a position of a reference pixel is selected based on a detection result, a value of a target pixel is predicted based on a value of the selected reference pixel, and based on the prediction result. A predictive coding method characterized by performing coding. 13. The predictive coding method according to claim 12, wherein whether or not the image is a dither image is detected as a characteristic based on the image. 14. The predictive coding method according to claim 12, wherein a code amount after coding is detected as a characteristic based on an image. 15. The predictive coding method according to claim 12, wherein the position of the reference pixel is selected for each predetermined line. 16. An image processing apparatus comprising the predictive coding apparatus according to any one of 1 to 6 and the decoding apparatus according to any one of 7 to 11.