JP3639624B2 - Encoding apparatus and method thereof - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an encoding apparatus and method for encoding image data using orthogonal transform processing .
[0002]
[Prior art]
Conventionally, in compression coding of an image signal using orthogonal transform, for example, discrete cosine transform (DCT), horizontal / vertical frequency components (DCT coefficients) in a block (8 × 8 pixels) that is blocked in a frame. Bit allocation is performed in accordance with (). That is, the high-frequency component is roughly quantized with respect to the low-frequency component, and a lot of quantization noise appears in the high-frequency component, and mosquito noise is generated when decoding, and the image quality is deteriorated.
[0003]
In order to reduce the deterioration of image quality due to such noise, when there is a correlation between the fields in the block (hereinafter, the correlation between the fields in the block is simply referred to as correlation), 8 × 8 in the frame. The pixel DCT processing is performed. When there is a motion in the block and there is no correlation, the DCT processing of 4 × 8 pixels in the field is performed to keep the DCT coefficient in the high frequency region low. Thus, conventionally, the correlation of all pixels in a block has been used for processing selection when encoding data in the block. That is, if the correlation is weak, the high-frequency coefficient of the intra-frame DCT increases and the coding efficiency decreases, so the intra-field DCT is selected.
[0004]
FIG. 6 is a block diagram showing a configuration of a conventional encoding apparatus. In the figure, 201 is a block circuit having a frame memory, 202 is a field data distributor, 203 is a subtractor, 204 is an absolute value circuit, 205 is an adder circuit, 206 is a decision circuit, 207 is a buffer memory, 208 is a selector, Reference numeral 209 denotes a frame orthogonal transform circuit, and 210 denotes a field orthogonal transform circuit.
[0005]
In FIG. 6, the data in the image processing block read from the blocking circuit 201 is second field data that is delayed by one field from the first field data and the first field data by the field data distributor 202. And divided. The difference absolute value of the two data output from the field data distributor 202 is calculated by the subtracter 203 and the absolute value circuit 204, and the sum of the difference absolute values in the block is calculated by the adding circuit 205. The output of the adder circuit 205 represents a correlation, and the determination circuit 206 determines the strength of the correlation.
[0006]
Further, the image data read from the blocking circuit 201 is adjusted by the buffer memory 207 until a correlation determination result is output by the determination circuit 206. When processing is selected via the selector 208 by the output of the determination circuit 206, the data read from the buffer memory 207 is processed by the frame orthogonal transform circuit 209 or the field orthogonal transform circuit 210.
[0007]
FIG. 7 is an explanatory diagram showing a conventional orthogonal transform. In the figure, the data in the image processing block read from the blocking circuit 201 is the sum of the absolute values of the difference between the first field pixel and the second field pixel one field after the pixel (arrow part in the figure). The threshold value of the determination circuit 206 is used to determine the strength of correlation between fields in the block. If it was determined that the correlation was strong, frame orthogonal transformation, that is, intra-frame 8 × 8 DCT processing was performed. On the other hand, if it is determined that the correlation is weak, field orthogonal transformation, that is, in-field 4 × 8 DCT processing has been performed.
[0008]
[Problems to be solved by the invention]
However, in the above-described conventional method, when the data in the image processing block is correlated by two lines, for example, in the case where the data in the image processing block is FIG. A large difference is produced when the correlations of the data (1) shifted by one line (FIG. 7B) are compared. That is, in FIG. 7A, the correlation is strong, but in FIG. 7B, the correlation is weak. Therefore, field processing (4 × 8 DCT processing in the field) is performed in FIG. 7B. When 4 × 8 DCT processing is performed in FIG. 7B, the intra-block data is rearranged as shown in FIG. 7C, and both the first and second field pixel columns have the highest frequency, and FIG. The block B) will have the highest vertical frequency. As described above, in the conventional orthogonal transform using the correlation determination, the coefficient in the high frequency region is increased, which may reduce the encoding efficiency.
[0009]
The present invention aims to provide a mark Goka apparatus and method Ru can be reduced coefficients of the high frequency region.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, an encoding apparatus according to the present invention includes a blocking unit that divides input image data into blocks each composed of a plurality of pixels, and a first pixel unit for each vertical pixel column in the block. Absolute value calculation means for sequentially calculating the absolute value of the value obtained by accumulating the difference between the pixel value of the field and the pixel value of the second field in the vertical direction, and the pixels in the vertical direction within the block by the absolute value calculation means Maximum value detection means for detecting a maximum absolute value among absolute values sequentially calculated for each column, comparison means for comparing the maximum absolute value detected by the maximum value detection means with a predetermined threshold value, and the comparison means comparison result, said maximum absolute value and a predetermined larger than the threshold is encoded field orthogonal transform process, encoding means for encoding by frames orthogonal transformation process otherwise the And it features.
[0011]
In order to achieve the above object, the encoding device of the present invention includes a blocking unit that divides input image data into blocks each composed of a plurality of pixels, and a vertical pixel column in the block. Absolute value calculation means for sequentially calculating the absolute value of a value obtained by accumulatively adding the difference between the pixel value of the first field and the pixel value of the second field in the vertical direction, and in the vertical direction within the block by the absolute value calculation means Counting means for counting the number of absolute values exceeding a reference value among absolute values sequentially calculated for each pixel column, comparison means for comparing the number counted by the counting means with a predetermined threshold, and the comparison If the counted number is larger than the predetermined threshold, the field orthogonal transform process is used for encoding. Otherwise, the frame orthogonal transform process is used for encoding. And having a means.
[0012]
In order to achieve the above object, the encoding device of the present invention includes a blocking unit that divides input image data into blocks each composed of a plurality of pixels, and a vertical pixel column in the block. Absolute value calculation means for sequentially calculating the absolute value of a value obtained by accumulatively adding the difference between the pixel value of the first field and the pixel value of the second field in the vertical direction, and in the vertical direction within the block by the absolute value calculation means A maximum value detecting means for detecting a maximum absolute value from absolute values sequentially calculated for each pixel column, and a first absolute value for comparing the maximum absolute value detected by the maximum value detecting means with a first threshold value. A comparison means; a counting means for counting the number of absolute values exceeding a reference value among the absolute values sequentially calculated for each vertical pixel column in the block by the absolute value calculating means; and Yo The comparison result of the second comparison means for comparing the counted number with the second threshold, and the comparison result of the first and second comparison means, the case where the maximum absolute value is larger than the first threshold and the count was encoded when at least one condition is satisfied by the field orthogonal transform processing in the case where the number is greater than the second threshold value, having a coding means for coding in a frame orthogonal transform otherwise It is characterized by .
[0013]
In order to achieve the above object, the encoding method of the present invention divides input image data into blocks each composed of a plurality of pixels, and the first field of each pixel column in the vertical direction in the block. The absolute value of the value obtained by cumulatively adding the difference between the pixel value and the pixel value of the second field in the vertical direction is sequentially calculated, and the maximum absolute value is calculated from the absolute values sequentially calculated for each vertical pixel column in the block. A value is detected, the detected maximum absolute value is compared with a predetermined threshold value, and if the maximum absolute value is greater than the predetermined threshold value as a result of the comparison, field orthogonal transform processing is performed, otherwise The encoding is performed by performing frame orthogonal transform processing.
[0014]
In order to achieve the above object, the encoding method of the present invention divides input image data into blocks each composed of a plurality of pixels, and the first field of each pixel column in the vertical direction in the block. The absolute value of the value obtained by accumulating the difference between the pixel value and the pixel value of the second field in the vertical direction is sequentially calculated, and the reference value is selected from the absolute values sequentially calculated for each vertical pixel column in the block. The number of absolute values exceeding the number is counted, and the counted number is compared with a predetermined threshold value. If the counted number is larger than the predetermined threshold value as a result of the comparison, field orthogonal transform processing is performed for encoding. Otherwise, encoding is performed by performing frame orthogonal transform processing.
[0015]
In order to achieve the above object, the encoding method of the present invention divides input image data into blocks each composed of a plurality of pixels, and the first field of each pixel column in the vertical direction in the block. The absolute value of the value obtained by cumulatively adding the difference between the pixel value and the pixel value of the second field in the vertical direction is sequentially calculated, and the maximum absolute value is calculated from the absolute values sequentially calculated for each vertical pixel column in the block. A value is detected, the detected maximum absolute value is compared with a first threshold value, and the number of absolute values exceeding a reference value among the absolute values sequentially calculated for each pixel column in the vertical direction in the block And comparing the counted number with a second threshold, and as a result of the comparison, when the maximum absolute value is greater than the first threshold and when the counted number is greater than the second threshold. If at least one of the conditions If plus is encoded field orthogonal transform processing, characterized by encoded frame orthogonal transform otherwise.
[0023]
【Example】
An embodiment of the encoding apparatus of the present invention will be described.
[0024]
[First embodiment]
FIG. 1 is a block diagram showing a configuration of an encoding apparatus. In the figure, 1 is an 8 × 8 block circuit, 2 is a processing selection circuit, 3 is an orthogonal transformation circuit, 4 is an input terminal for field data, 5 is a frame memory, 6 is a read address generator for the frame memory, and 7 is Frame memory write address generator, 8 is an adder / subtracter, 9 is an absolute value circuit, 10 is a comparator, 11 is a buffer memory, 12 is an 8 × 8 DCT circuit that performs frame processing, and 13 is 4 × 8 that performs field processing DCT circuit.
[0025]
Reference numeral 14 denotes a selector, 15 denotes an output terminal for orthogonal transform coefficients, 16 denotes a format selection terminal, 17 denotes a threshold value determination circuit, and 18 denotes a maximum value circuit.
[0026]
Image data input in field units from the field data input terminal 4 is written to an address output from the write address generator 7 of the frame memory 5 and read out by the read address generator 6 so as to be read out in units of 8 × 8 pixel blocks. It is read from the output address and is blocked. At this time, the read address generator 6 generates an address so that the data in the block is read in the order of pixel numbers, that is, in the vertical direction.
[0027]
The block data in units of 8 × 8 pixels output from the block forming circuit 1 is input to the processing selection circuit 2, and the absolute value of the field difference from the pixel 1 to the pixel 8 by the adder / subtractor 8 and the absolute value circuit 9, and then the pixel The absolute value of the field difference from 9 to the pixel 18... The absolute value of the field difference from the pixel 57 to the pixel 64 is calculated.
[0028]
When the absolute values of the eight types of blocks are output continuously from the absolute value circuit 9, the maximum value circuit 18 detects the maximum value of the eight types of absolute values in the block, and the comparator 10 outputs the maximum value circuit 18. The threshold value TH output from the threshold value determination circuit 17 is compared, and comparison information between the maximum absolute value and the threshold value TH is output.
[0029]
The data output from the frame memory 5 and input to the buffer memory 11 has the output timing of the comparison information output from the processing selection circuit 2 in the buffer memory 11 and the two kinds of orthogonal transform outputs in the orthogonal transform circuit 3. Delayed to match.
[0030]
Data output from the buffer memory 11 is input to the orthogonal transform circuit 3. In the selector 14, one of the two types of DCT processes is selected based on the comparison information output from the process selection circuit 2. The orthogonal transform circuit 3 includes an 8 × 8 DCT circuit 12 that performs orthogonal transform regardless of the field data in the block, and a 4 × 8 that performs orthogonal transform on the first and second fields in the block in units of fields. A DCT circuit 13 is provided, and any DCT process selected by the comparison information is performed.
[0031]
The DCT coefficient data of the selected process is output from the output terminal 15 for orthogonal transform coefficients. Also, format information such as SD / HD / other methods is input from the format selection terminal 16, and a threshold value TH suitable for each format is output from the threshold value determination circuit 17.
[0032]
FIG. 2 is an explanatory diagram showing image data in the image processing block. In the figure, if the image data in the image processing block (64 pixels) is pixels P1, P2,..., P64, ABS (P1-P2 + P3-P4 + P5-P6 + P7-P8),. -P62 + P63-P64) is calculated. Here, ABS represents an absolute value.
[0033]
This is for calculating the correlation of one column in the vertical direction in the block. The larger the absolute value is, the smaller the correlation is, the movement is present in the block, and the vertical frequency component caused by the movement is increased. ing. When orthogonal transformation is performed on a block in which motion exists in this way, it is preferable to perform 4 × 8 DCT processing in the field because the DCT coefficients can be concentrated in a low frequency range, which is preferable in terms of coding efficiency.
[0034]
[Second Embodiment]
FIG. 3 is a block diagram showing the configuration of the encoding apparatus according to the second embodiment. In the figure, 601 is a data input terminal, 602 is an 8 × 8 pixel block circuit, 603 is an adder / subtracter, 604 is an absolute value circuit, 605 is a comparator, 606 is a counter, 607 is a counter output comparator, and 608 is a buffer memory. , 609 are format selection terminals, 610 is a threshold / counter comparison value determination circuit, 611 is an orthogonal transformation circuit, and 612 is an output terminal for orthogonal transformation coefficients.
[0035]
The field unit image data input from the data input terminal 601 is input to the blocking circuit 602 including the frame memory as in the first embodiment. The data is converted into frames by the block forming circuit 602, and data in units of blocks composed of 8 × 8 pixels is output. When the output data of the block forming circuit 602 is input to the adder / subtractor 603, the adder / subtracter 603 calculates the correlation of 8 pixels in the vertical direction, and the absolute value circuit 604 calculates the absolute value of the correlation in each of the 8 columns in the horizontal direction. . The output of the absolute value circuit 604 is input to the comparator 605 and compared with the threshold value TH output from the threshold value / counter comparison value determination circuit 610.
[0036]
The output of the comparator 605 is 8 data in the block, and the counter 606 counts the number of columns in the block where the output of the absolute value circuit 604 is greater than the threshold value TH. When the count output is input to the counter output comparator 607, it is compared with the counter output comparison value output from the threshold / counter comparison value determination circuit 610, and the counter output comparator 607 outputs the comparison result.
[0037]
The data output from the blocking circuit 602 and input to the buffer memory 608 is input to the orthogonal transform circuit 611 and output from the frame orthogonal when the output timing is adjusted in the buffer memory 608 as in the first embodiment. Transformation or field orthogonal transformation processing is performed. The selection of the two types of orthogonal transform is performed by the output of the counter output comparator 607, and the field orthogonal transform is selected when the output of the counter 606 is larger than the counter output comparison value. The output of the orthogonal transform circuit 611 is output from an output terminal 612 for orthogonal transform coefficients.
[0038]
The threshold value TH / counter output comparison value is determined by the threshold value / counter comparison value determination circuit 610 as an appropriate numerical value corresponding to the format information input from the format selection terminal 609.
[0039]
FIG. 4 is an explanatory diagram showing image data in the image processing block. Image data is output from the blocking circuit 602 in the order of pixel numbers. As with the first embodiment, for the block data, the correlation from pixel 1 to pixel 8 is first calculated as ABS (P1-P2 + P3-P4 + P5-P6 + P7-P8). Correlation is similarly calculated for other vertical columns (the closer to 0, the stronger the correlation). These eight types of correlation are compared with the threshold value TH, and the counter 606 counts the number of columns in which the correlation is greater than the threshold value TH (a column with weak correlation).
[0040]
The output of the counter 606 is compared with the counter output comparison value. If the output is larger than the counter output comparison value, it is determined that the block of interest is a block having many weakly correlated columns, and field orthogonal transformation is selected.
[0041]
According to the encoding apparatus of the second embodiment, since the weakly correlated columns are counted, the threshold value TH is made smaller than in the first embodiment in which weak correlation is detected by the weakest correlation value in the block. It is possible. Therefore, even in a low-contrast block whose intra-block image data is not determined to be field orthogonal transform by the threshold value TH of the first embodiment, a block having a weakly correlated column in the vertical direction in the block is determined. Is possible.
[0042]
[Third embodiment]
Next, an encoding apparatus according to the third embodiment will be described. FIG. 5 is a block diagram showing the configuration of the encoding apparatus of the third embodiment. In the figure, 801 is a data input terminal, 802 is an 8 × 8 pixel blocking circuit, 803 is an adder / subtracter, 804 is an absolute value circuit, 805 and 806 are comparators A, B and 807 are counters, and 808 is a counter output comparison. 809 is a determination circuit, 810 is a buffer memory, 811 is a format selection terminal, 812 is a threshold value / counter comparison value determination circuit, 813 is an orthogonal transformation circuit, 814 is an output terminal for an orthogonal transformation coefficient, and 815 is a maximum value circuit. It is.
[0043]
For the data input from the data input terminal 801, the correlation in the vertical direction in the block is calculated by the block forming circuit 802, the adder / subtractor 803, and the absolute value circuit 804 as in the first and second embodiments. In the vertical direction in the block, the maximum vertical direction correlation in the block is obtained by the maximum value circuit 815, the comparator A805, and the threshold value TH1 as in the first embodiment, and the comparator B806, the counter 807, and the counter output comparator 808 are obtained. , Threshold TH2, and counter output comparison value, the number of columns with weak correlation in the vertical direction in the block is obtained in the same manner as in the second embodiment. The output of the comparator A 805 and the output of the counter output comparator 808 are input to the determination circuit 809, and the determination circuit 809 outputs selection determination information for field orthogonal transformation or frame orthogonal transformation.
[0044]
With respect to the image data whose timing is adjusted by the buffer memory 810, two types, that is, frame DCT processing and field DCT processing are performed by the orthogonal transformation circuit 813. One orthogonal transform coefficient data is selected by the selection determination information output from the determination circuit 809, for example, the logical sum of the output of the comparator A805 and the output of the counter output comparator 808, and is output from the output terminal 814 of the orthogonal transform coefficient.
[0045]
According to the coding apparatus of the third embodiment, it is possible to efficiently detect a block in which a column having a weak vertical correlation exists regardless of the level of contrast. Further, by feeding back the output of the maximum value circuit 815 or the output of the counter 807 to the threshold value / counter comparison value determination circuit 812, the maximum vertical direction correlation in the block and the number of columns with weak vertical direction correlation are met. It is also possible to determine the threshold value, for example, to decrease the threshold value TH2 with respect to the increase in the output of the maximum value circuit 815.
[0046]
【The invention's effect】
According to the present invention, for each vertical pixel column in the block, the absolute value of the value obtained by cumulatively adding the difference between the pixel value of the first field and the pixel value of the second field in the vertical direction is sequentially calculated, A maximum absolute value is detected from absolute values sequentially calculated for each pixel column in the vertical direction in the block, and the detected maximum absolute value is compared with a predetermined threshold value. If it is larger than the predetermined threshold value, the field orthogonal transform process is used for encoding. Otherwise, the frame orthogonal transform process is used for encoding. correlation determination between blocks within a field even when the shift line does not change, it is the frame processing of the correlation strength, Ru can avoid selecting a field processing is mishandled. Result of this, the orthogonal transform coefficients due to the motion is reduced, it can be made higher than the conventional encoding efficiency.
[0047]
According to the present invention, the absolute value of the value obtained by cumulatively adding the difference between the pixel value of the first field and the pixel value of the second field in the vertical direction is sequentially calculated for each vertical pixel column in the block. , Counting the number of absolute values exceeding a reference value from absolute values sequentially calculated for each pixel column in the vertical direction in the block, comparing the counted number with a predetermined threshold, the comparison result, When the counted number is larger than the predetermined threshold value, the field orthogonal transform process is used for encoding, and in other cases, the frame orthogonal transform process is used for encoding. In a block, even if the line is shifted in the vertical direction, the judgment of the correlation between the fields in the block does not change, and the frame processing with strong correlation is selected. It can be avoided. In addition, the correlation between fields can be accurately determined even in a block having a low contrast. As a result, the orthogonal transform coefficient resulting from the motion is reduced, and the coding efficiency can be increased as compared with the conventional case.
[0048]
Further, according to the present invention, the correlation between fields is determined by accumulating the difference between the pixel value of the first field and the pixel value of the second field in the vertical direction for each vertical pixel column in the block. The absolute values of the obtained values are sequentially calculated, the maximum absolute value is detected from the absolute values sequentially calculated for each pixel column in the vertical direction in the block, and the detected maximum absolute value and the first threshold value are detected. And count the number of absolute values exceeding a reference value from the absolute values sequentially calculated for each pixel column in the vertical direction in the block, and compare the counted number with a second threshold value. As a result of the comparison, if the maximum absolute value is larger than the first threshold and if at least one condition of the counted number is larger than the second threshold is satisfied, field orthogonal transform processing is performed for encoding. , Otherwise Since the encoding is performed by the frame orthogonal transformation process, in the block having a correlation for each two lines, which has been a problem in the past, the judgment of the correlation between the fields in the block does not change even when the line is shifted in the vertical direction. The frame processing is strongly correlated, and it is possible to avoid selecting field processing that is erroneous processing. Further, regardless of the high low contrast, can accurately determine the correlation between fields, as a result, the orthogonal transform coefficients due to the motion is reduced, it can be made higher than the conventional encoding efficiency.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an encoding device.
FIG. 2 is an explanatory diagram showing image data in an image processing block.
FIG. 3 is a block diagram showing a configuration of a coding apparatus according to a second embodiment.
FIG. 4 is an explanatory diagram showing image data in an image processing block.
FIG. 5 is a block diagram showing a configuration of a coding apparatus according to a third embodiment.
FIG. 6 is a block diagram illustrating a configuration of a conventional encoding device.
FIG. 7 is an explanatory diagram showing a conventional orthogonal transform.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,601,801 ... Blocking circuit 18,815 ... Maximum value circuit 606,807 ... Counter 3,612,813 ... Orthogonal transformation circuit

Claims (6)

Blocking means for dividing input image data into blocks composed of a plurality of pixels ,
Absolute value calculation means for sequentially calculating absolute values of values obtained by cumulatively adding the difference between the pixel value of the first field and the pixel value of the second field in the vertical direction for each vertical pixel column in the block;
Maximum value detecting means for detecting a maximum absolute value from absolute values sequentially calculated for each pixel column in the vertical direction in the block by the absolute value calculating means;
Comparing means for comparing the maximum absolute value detected by the maximum value detecting means with a predetermined threshold;
A comparison result of the comparison means; and a coding means for coding by performing field orthogonal transformation processing when the maximum absolute value is larger than the predetermined threshold, and encoding by frame orthogonal transformation processing otherwise. A characteristic encoding apparatus. Blocking means for dividing input image data into blocks composed of a plurality of pixels ,
Absolute value calculation means for sequentially calculating absolute values of values obtained by cumulatively adding the difference between the pixel value of the first field and the pixel value of the second field in the vertical direction for each vertical pixel column in the block;
Counting means for counting the number of absolute values exceeding a reference value from absolute values sequentially calculated for each pixel column in the vertical direction in the block by the absolute value calculating means;
Comparing means for comparing the number counted by the counting means with a predetermined threshold;
And a coding means for coding by performing field orthogonal transform processing when the counted number is larger than the predetermined threshold as a result of comparison by the comparing means, and encoding by frame orthogonal transform processing otherwise. An encoding device characterized by the above. Blocking means for dividing input image data into blocks composed of a plurality of pixels ,
Absolute value calculation means for sequentially calculating absolute values of values obtained by cumulatively adding the difference between the pixel value of the first field and the pixel value of the second field in the vertical direction for each vertical pixel column in the block;
Maximum value detecting means for detecting a maximum absolute value from absolute values sequentially calculated for each pixel column in the vertical direction in the block by the absolute value calculating means;
First comparing means for comparing the maximum absolute value detected by the maximum value detecting means with a first threshold;
Counting means for counting the number of absolute values exceeding a reference value from absolute values sequentially calculated for each pixel column in the vertical direction in the block by the absolute value calculating means;
Second comparison means for comparing the number counted by the counting means with a second threshold value;
When the comparison result of the first and second comparison means satisfies at least one of a condition where the maximum absolute value is greater than the first threshold and a case where the counted number is greater than the second threshold. An encoding device comprising: encoding means for encoding by performing field orthogonal transform processing; otherwise, encoding by performing frame orthogonal transform processing . Divide the input image data into blocks composed of multiple pixels,
  For each vertical pixel column in the block, sequentially calculate the absolute value of the value obtained by cumulatively adding the difference between the pixel value of the first field and the pixel value of the second field in the vertical direction,
  The maximum absolute value is detected from the absolute values sequentially calculated for each pixel column in the vertical direction in the block,
  Comparing the detected maximum absolute value with a predetermined threshold;
  As a result of the comparison, if the maximum absolute value is larger than the predetermined threshold, encoding is performed by performing field orthogonal transform processing; otherwise, encoding is performed by performing frame orthogonal transform processing. Divide the input image data into blocks composed of multiple pixels,
  For each vertical pixel column in the block, sequentially calculate the absolute value of the value obtained by cumulatively adding the difference between the pixel value of the first field and the pixel value of the second field in the vertical direction,
  The absolute value that is sequentially calculated for each pixel column in the vertical direction within the block exceeds the reference value. Count the number of absolute values,
  Comparing the counted number with a predetermined threshold;
  As a result of the comparison, if the counted number is larger than the predetermined threshold, encoding is performed by field orthogonal transform processing, and otherwise, encoding is performed by frame orthogonal transform processing. Divide the input image data into blocks composed of multiple pixels,
  For each vertical pixel column in the block, sequentially calculate the absolute value of the value obtained by cumulatively adding the difference between the pixel value of the first field and the pixel value of the second field in the vertical direction,
  The maximum absolute value is detected from the absolute values sequentially calculated for each pixel column in the vertical direction in the block,
  Comparing the detected maximum absolute value with a first threshold;
  Counting the number of absolute values exceeding the reference value from the absolute values sequentially calculated for each pixel column in the vertical direction in the block,
  Comparing the counted number with a second threshold;
  As a result of the comparison, if the maximum absolute value is greater than the first threshold and if at least one of the cases where the counted number is greater than the second threshold, the field orthogonal transform process is performed and encoded. In other cases, the encoding method is characterized by performing encoding by performing frame orthogonal transform processing.

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