JP2002051338A - Orthogonal transformation apparatus and orthogonal transformation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce redundancy in processing period, when a block with pixels whose number is lower than n by n is subjected to orthogonal transformation. SOLUTION: In the case of a block 300 at a corner, only regions of effective pixels excluding a pixel supplement region are written into a storage section, and only the regions of the written effective pixels are read out from the storage section. Then, after a first one-dimensional orthogonal transformation is performed, the result of transformation is also written back into the addresses which is read out in the storage section. Thereafter, as a direction in which a one-dimensional orthogonal transformation is to be performed, the pixel data is read out with the order of horizontal and vertical directions changed in the order, and a two-dimensional orthogonal transformation is performed. At this time, the result of transforming the effective pixel region, such as the read-out in the one-dimensional orthogonal transformation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an orthogonal transformation apparatus and an orthogonal transformation method for performing orthogonal transformation on image data input in units of n × n pixels.

[0002]

2. Description of the Related Art In a conventional configuration example, a unit size of an input pixel block to be subjected to two-dimensional orthogonal transform is set to n × n pixels, and this is referred to as an orthogonal transform block. As an example, as shown in FIG.
If the size in the vertical direction is 634 pixels and 475 pixels, respectively, and the unit size of the input pixel block is 8 × 8, it is necessary to supplement data at the end of the image to generate an orthogonal transformation block. As a value to be supplemented, a method of repeating a value at the end of an image is generally known.

[0003] An example of the configuration of a conventional two-dimensional orthogonal transform apparatus and the processing of each unit will be described below.

An input pixel supply device as an input pixel value repetition unit receives an input value (input pixel row) from an external information source, and sequentially sends the received input pixel row to the subsequent stage in units of orthogonal transform blocks. At this time, if the size of the orthogonal transform block being processed is less than the unit size n × n, the value of the end portion of the image is repeated, and the data of the orthogonal transform block is transmitted to the subsequent stage so that the orthogonal transform block satisfies the unit size. send.

The data of the orthogonal transformation block output from the input pixel value repetition unit is input to a selection unit (selector). The selector selects one of the output value of the input pixel supply device (the data of the orthogonal transform block) and the output value of the one-dimensional orthogonal transform device (the result of the first orthogonal transform) and outputs it to the storage unit 1. The selection process in the selector is determined according to the output signal from the control device.

The storage unit 1 holds the data of the orthogonal transform block for the unit size of the orthogonal transform block, and reads out the data to the storage unit 2 shown later. At this time, the reading of the data of the orthogonal transformation block from the storage unit 1 is performed in units of n (pixels), and when the reading of n units is performed from the storage unit 1, the read n units are stored. The output value from the selector is newly written in the storage area in the storage unit 1 that has been used.

In the same manner, after reading n × n values from the storage unit 1 and writing new n × n values into the storage unit 1, the data stored in the storage unit 1 Then, the data arrangement in the horizontal direction and the data arrangement in the vertical direction are switched, and the data is read out to the storage unit 2 in units of n units. Control of writing to and reading from the storage unit 1;
Timing is performed according to the output of the control device.

The data output from the storage unit 1 is stored in the storage unit 2
When n data, which is the unit size in the one-dimensional direction of the orthogonal transformation block, is stored in the storage unit 2, the data is simultaneously output to the one-dimensional orthogonal transformation unit. The timing for accumulating and outputting the n values is managed by a control device, and a control signal from the control device is output to the storage unit 2, and the storage unit 2 operates according to the timing of the control signal.

The one-dimensional orthogonal transformation unit performs one-dimensional orthogonal transformation on the n values output from the storage unit 2 to obtain a new n
These values are created and sequentially output to the selector and the outside (as a result of the two-dimensional orthogonal transformation).

[0010] The control device controls the operation timing of the selector, the storage unit 1 and the storage unit 2. The control signal for the selector is such that the orthogonal transform block being processed by the one-dimensional orthogonal transform unit is 1
While the first one-dimensional orthogonal transformation is being performed and the processing result is sequentially output, the first orthogonal transformation result is selected. While the first one-dimensional orthogonal transformation is being performed and the processing result is sequentially output, the data string of the next processing block (input pixel string in units of orthogonal transformation blocks output from the input pixel repeating unit) is selected. It is a signal like this.

The control signal for the storage unit 1 is such that the output from the selector is written into the storage unit 1 in units of n units, and the output to the storage unit 2 is output from the storage unit 1 in units of n units. The control signal is such that the reading and the writing and the reading are alternately performed.

A control signal for the storage unit 2 is stored in the n buffers in order of n values sequentially read from the storage unit 1 for n buffers in the storage unit 2. Control signal.

FIG. 9 shows an operation timing example of each element in the configuration of the conventional example. Hereinafter, the operation timing of the conventional example will be described with reference to FIG.

In the period 11a, the input block size 920 of the block N input from the information source is input to the input pixel supply device. The input pixel supply device converts the input pixel column from the information source to n based on the value of the input block size 920.
Receive until the block becomes × n. Input pixel column 912
Are output n times each in a period 11b, a period 12b,..., A period 1nb. In the case of the next block (N + 1), n signals are output n times in the same manner in the period 31b, the period 32b,..., The period 3nb. Hereinafter, the subsequent blocks are similarly output.

The output of control signal 917 to the selector is:
Each changes at the beginning of the period 11a, the period 21a, the period 31a,. When the period corresponds to the data fetch period of each block, the control signal 917 outputs the input pixel column 912.
In other words, it indicates the first one-dimensional orthogonal transformation result side selection.

The output 913 of the selector is performed n times n times each in the period 11b, the period 12b,..., The period 1nb, and these are the input values of the block N.
Is the value to be written to Further, the period 21b and the period 22
b,..., n times are output n times in the period 2nb. These are the results of the first orthogonal transformation processing of the block N, and are the values written to the storage unit 1.
Further, in the period 31b, the period 32b,..., The period 3nb, n outputs are performed n times each, and these are the input values of the block (N + 1) and the write values to the storage unit 1. Hereinafter, the same applies to the subsequent blocks.

The change of the control signal 918 to the storage unit 1 is performed during the period 11a, the period 11b, the period 12a, and the period 12a.
b,..., period 1na, period 1nb, period 21a, period 2
1b, period 22a, period 22b,..., Period 2na, period 2nb, period 31a, period 31b, period 32a, period 3
2b,..., Period 3na, period 3nb,. Further, the control signal 918 is in the period 1
, Period 1na, period 21a, period 22a,..., Period 22a,... Indicates reading, and other periods indicate writing. In this operation timing example, the read value in the period 11a, the period 12a,..., The period 1na is the result of the second orthogonal transformation of the block (N-1). The write value to the block N is the input value of the block N, and the read value from the storage unit 1 in the period 21a, the period 22a,... , ..., period 2
nb, the value written to the storage unit 1 is 1 in block N.
It means the result after the second orthogonal transformation. Storage unit 1
Output values 914 from the period 11a, the period 12a,.
The data is output from the storage unit 1 n × n times n times during the period 1na, and these are the results of the first orthogonal transform of the block (N−1). .., 2na are output from the storage unit 1 n × n times, and these are input values of the block N. Further, the data is output from the storage unit 1 n times n × n times in the period 31a, the period 32a,.
Is the result of the first orthogonal transformation of.

The storage unit 2 accumulates n values of the output value 914 output during the above-described period, and stores the output value 914 as the output value 915 of the storage unit 2 during the periods 11b, 12b,.
b, period 21b, period 22b, ..., period 2nb, period 3
1b, period 32b,..., Period 3nb.

The one-dimensional orthogonal transformation unit receives the input of the output value 915 from the storage unit 2, performs one-dimensional orthogonal transformation on n values, and sequentially generates the newly generated n values for the period 11.
b, period 12b,..., period 1nb, period 21b, period 2
, Period 2nb, period 31b, period 32b,.
Output at the timing of the period 3nb,. At this time, the output value 916 of the one-dimensional orthogonal transform unit in the period 11b, the period 12b,...
Means the two-dimensional orthogonal transformation result of period 21b and period 22
b,..., the output value 916 in the period 2nb is the block N
Means the result of the first one-dimensional orthogonal transformation of
The output value 916 in the period 32b,..., 3nb means the result of the two-dimensional orthogonal transformation of the block N.

FIG. 4 is a diagram for explaining the reading order of values in the storage unit 1.

Assuming that the order shown in FIG. 2A is the input order of values in units of orthogonal transform blocks, the order of reading from the storage unit 1 for the first one-dimensional conversion in each orthogonal transform block. Is the order shown in FIG. 7A, and the reading order from the storage unit 1 for the second one-dimensional conversion in each orthogonal transformation block is the order shown in FIG. As described above, the two-dimensional orthogonal transformation is realized by switching the reading order for the first and second one-dimensional transformations in the row direction and the column direction, respectively.

[0022]

However, in the conventional configuration, the processing of the block including the pixel replacement area requires the same processing time as the processing of the block not including the pixel replacement area, and the processing time of the entire image is reduced. There was a problem that it became redundant.

The present invention has been made in view of the above problems, and when performing orthogonal transformation on a block having less than n × n pixels, an orthogonal transformation apparatus and an orthogonal transformation apparatus for reducing redundancy in a processing period. It is intended to provide a conversion method.

[0024]

In order to achieve the object of the present invention, for example, an orthogonal transform apparatus of the present invention has the following arrangement. That is, the image data input in units of n × n pixels, the first selecting means for selecting one of the one-dimensional orthogonally transformed image data, and the image data selected by the first selecting means are stored. Storage means for extracting the image data stored in the storage means in units of n pixels in a horizontal or vertical direction, and a second means for selectively extracting n pixels from the pixel data extracted by the extraction means. Selection means, orthogonal transformation means for performing one-dimensional orthogonal transformation on pixel data selectively extracted by the second selection means, and extraction means for blocks less than n × n pixels. And control means for controlling so as to change the selection direction by the second selection means.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail according to preferred embodiments with reference to the accompanying drawings.

FIG. 1 shows the configuration of a two-dimensional orthogonal transform apparatus according to this embodiment.

Reference numeral 111 denotes an input value of an image to be processed, which is input from an external information supply source. It is assumed that the input value is divided into blocks of n pixels × n pixels as a unit for orthogonal transformation.

Reference numeral 101 denotes a selection unit, which is an input value 111 of an image to be processed input from an external information supply source, an output 116 of the one-dimensional orthogonal transformation unit 105, and an output 11 of the control unit 106.
7 as input, and input values 111 and 1 from the external information source.
One of the output values 116 from the dimensional orthogonal transform unit 105 is selected and the value is output as the output value 112. Input value 111 from external information source and one-dimensional orthogonal transform unit 1
Which one of the output values 116 from 05 is selected is controlled by the output 117.

Reference numeral 102 denotes a storage unit which receives an output value 112 from the selection unit 101 and an output value 118 from the control unit 106 and outputs an output value 113.

The storage unit 102 stores the output value 112 from the selection unit 101 up to the unit size (n ×
n) hold it, read it out to the storage unit 103 shown later,
When reading is performed as much as necessary, the output value 112 of the selecting unit 101 is newly written to the address read immediately before. Thereafter, in the same manner, a maximum of n × n values are read out, and after a new maximum of n × n values are written, the data arrangement in the horizontal direction and the data arrangement in the vertical direction are switched to n. The data is read out to the storage unit 103 on a unit basis. Control and timing of writing and reading to and from the storage unit 102 are performed according to an output 118 of the control device 106.

For example, if the image size and the size of the orthogonal transformation block shown in FIG.
In the case of 0, only the effective pixel area excluding the pixel replacement area of the end block 300 is written in the storage unit 102, and the storage unit 1
After reading out only the area of the effective pixel from which the readout from 02 has been written, the first one-dimensional orthogonal transformation is performed, and then the conversion result is similarly written back to the read address in the storage unit 102. Thereafter, as the direction in which the one-dimensional orthogonal transformation is performed, the order of the horizontal and vertical directions is switched and read out, and the second one-dimensional orthogonal transformation is performed. In this case, the first 1
As in the reading at the time of the dimensional orthogonal transform, only the result obtained by converting the effective pixel area is read.

When processing the end block 301 of FIG. 3, only the effective pixel area excluding the pixel supplement area of the end block 301 is written in the storage unit 102, and readout is performed only in the effective pixel area. Then the first 1
After performing the dimensional orthogonal transform, the conversion result is written back to the read address of the storage unit 102, and the read is performed by switching the order in the horizontal and vertical directions.
Performs dimensional orthogonal transformation. Also at this time, only the result obtained by converting the effective pixel area is read.

The value 113 output from the storage unit 102 is input to the storage unit 103, and is output to the selection unit 104 when a maximum of n pieces of data have been accumulated. The output value is
The data is input to the selection unit 104 through a signal line 114 provided to transfer n pieces of data in parallel.

The selecting section 104 selects only necessary data from the n pieces of data input through the signal line 114 and outputs the selected data to a signal line 115 provided to transfer the n pieces of data in parallel. At this time, the selecting unit 104 determines which one of the n input units 114 is to be selected by the control unit 1.
06 output 120.

For example, when processing the end block 301 shown in FIG. 3, the result of the second one-dimensional orthogonal transformation is that 114 (1) to 114 (2) of the signal lines 114.
, The selection unit 104 determines 115 (2) to
For the signal lines 115 (n), values passing through the signal lines 114 (2) are all selected, and the signal lines 115 (2) to 115 (115) are respectively selected.
(N).

The one-dimensional orthogonal transform unit 105 compares the n values output from the selection unit 104 via the signal line 115 by 1
Perform a dimensional orthogonal transformation to create new n values 116,
The data is sequentially output to the selection unit 101 and the outside (to the outside, as a two-dimensional orthogonal transformation result).

The control unit 106 includes the selection unit 101 and the storage unit 1
02, the operation of the storage unit 103 and the operation of the selection unit 104 are controlled. The control signal 117 selects the processing result 116 while the orthogonal transformation block being processed by the one-dimensional orthogonal transformation unit 105 is performing the first one-dimensional transformation and sequentially outputting the processing result. And a one-dimensional orthogonal transform unit 10
While the orthogonal transformation block 5 being processed is performing the second one-dimensional transformation and sequentially outputting the processing result, the input value from the external information supply source, which is the data string of the next processing block, The signal is such that 111 is selected.

The control signal 118 to the storage unit 102 writes the output 112 of the selection unit 101 at a maximum of n units as one unit, and reads the output to the storage unit 103 at a maximum of n units as one unit. The control signal is such that writing and reading are alternately performed.

The control signal 119 to the storage unit 103 is transmitted to n storage buffers in the storage unit 103 by the storage unit 1.
The signal is a signal for controlling the storage unit 103 so that a maximum of n values sequentially read from 02 are sequentially stored in the buffer. The control signal 120 to the selection unit 104 is
The selection unit 1 selects only necessary data from n pieces of input data input via the signal line 114 and outputs n pieces of output data via the signal line 115.
04.

FIG. 2 shows an example of operation timing for each element shown in FIG. Hereinafter, FIG.
The operation timing of the orthogonal transform apparatus according to the present embodiment will be described with reference to FIG. In this operation timing example, it is assumed that the orthogonal transform block size is n pixels × n pixels.

In the period 11a, the input block size 121 of the block N input from the information source is
06. In this operation timing example, the block N is the end block of the image, and the orthogonal transform block size of the block N is 2 pixels in the horizontal direction and n in the vertical direction.
Let it be a pixel. Therefore, the input data 111 is input to the selecting unit 101 twice (n pixels each) twice in the period 11b and the period 12b (resulting in n
× 2 size block data is input). Also,
In the case of the next block (N + 1), period 3
1b, period 32b,..., Period 3nb
Is input to the time selection unit 101 (as a result, a block of size n × n is input). Hereinafter, the subsequent blocks are similarly input.

The control signal 117 for the selector 101 is:
Each changes at the beginning of the period 11a, the period 21a, the period 31a,. That is, when the period corresponds to the data capturing period of each block, the control signal 117 indicates the selection of the input data 111 side, and otherwise indicates the selection of the output 116 side from the one-dimensional orthogonal transform unit 105. Input data 11
1 is input twice to the selection unit 101 twice each in the period 11b and the period 12b, and these are the input values of the block N and the write values 112 to the storage unit 102. Further, in the period 21b and the period 22b, n
The output is performed twice each time, and these are the results 116 of the first orthogonal transformation processing of the block N.
3 is the value to be written. Further, in the period 31b, the period 32b,..., The period 3nb, n outputs are performed n times each, and these are the input values of the block (N + 1) and the write values to the storage unit 102. Hereinafter, the same applies to the subsequent blocks.

The change of the control signal 118 with respect to the storage unit 102 includes the period 11a, the period 11b, the period 12a, and the period 12
b, period 13a, period 14a, ..., period 1na, period 2
1a, period 21b, period 22a, period 22b, period 31
a, period 31b, period 32a, period 32b, ..., period 3
, na, 3nb,... at the beginning of the period. The control signal 118 indicates read or write at the timing shown in FIG. In this operation timing example, the period 11a, the period 12a,.
The read value at na is calculated based on the second one-dimensional orthogonal transformation result 116 of the block (N−1) in the period 11 b and the period 12.
The write value to the storage unit 102 in b is the input value of the block N and the storage unit 10 in the period 21a and the period 22a.
The read value from block 2 is the value before the first one-dimensional orthogonal transform of the block N, and the write value to the storage unit 103 in the periods 21b and 22b is the result after the first one-dimensional orthogonal transform of the block N. means.

The output value 113 from the storage unit 102 is output n times in each of the period 11a, the period 12a,..., The period 1na, n times. The result. Further, n signals are output twice in each of the period 21a and the period 22a, and these are input values of the block N. Further, the period 31a and the period 32
a,..., two times each in the period 3na, output n times,
These are the results of the first one-dimensional orthogonal transformation of block N.

The storage unit 103 accumulates n or two output values 113 output from the storage unit 102 during the above-mentioned period, and stores the output value 113 via the signal line 114 for the period 11.
b, period 12b, period 13a, period 14a,..., period 1
na, period 21b, period 22b, period 31b, period 32
,..., at the beginning of each period 3 nb.

The selection unit 104 controls the signal line 114 during the period.
Select from n or two values output via
In a method to be described later, n output values are output via the signal line 115 to the periods 11b, 12b, 13a, 14a,
..., period 1na, period 21b, period 22b, period 31
b, period 32b,..., period 3nb.

The one-dimensional orthogonal transform unit 105 includes a signal line 115
, And performs a one-dimensional orthogonal transformation on n values, and sequentially generates n values newly generated in a period 11b, a period 12b, a period 13a, a period 14a,..., A period 1na , Period 21b, period 22b, period 31b, period 32b,..., Period 3nb,. At this time, the period 11b, the period 12b, the period 13a,
The output value 116 of the one-dimensional orthogonal transform unit 105 in the periods 14a, ..., 1na means the result of the two-dimensional orthogonal transform of the block (N-1), and the output value 116 in the periods 21b and 22b is the first time of the block N , The period 31b, period 32b,..., Period 3nb
Means the two-dimensional orthogonal transform result of the block N.

FIG. 5 is a diagram for explaining the reading and writing order of values in the storage unit 103 when the orthogonal transformation block size n × n is 8 × 8 and the size of the current processing input block is 2 × 8 pixels. .

The order indicated by the arrows in FIG.
Assuming that the input order is the value in the unit of the orthogonal transform block, the order of reading from the storage unit 103 for the first one-dimensional conversion in the block N is the order shown in FIG. The order of reading from the storage unit 103 for the second one-dimensional orthogonal transformation is the order shown in FIG. Further, assuming that the input block is the above-described block N, the signal line 115 by the selection unit 104 during the period of the first one-dimensional orthogonal transformation processing of the block N is, as shown in FIG.
The n values input via the line 4 are directly output to the signal line 115 on a one-to-one basis. Also, during the period of the second one-dimensional orthogonal transformation processing of the block N, the signal line 115 by the selection unit 104 is also as shown in FIG. As described above, the reading order for the first and second one-dimensional conversions is switched in the row direction and the column direction, respectively, to perform the two-dimensional orthogonal conversion. The processing of the end blocks, including reading and writing from the storage unit 103, is minimized by minimizing
The processing period as a whole can be shortened.

FIG. 6 shows another example of the sequence of reading and writing values in the storage section 103 when the orthogonal transform block size n × n is 8 × 8 and the size of the current processing input block is 8 × 2 pixels. FIG.

Assuming that the order shown in FIG. 6A is the input order of values in units of orthogonal transform blocks, the storage unit 1 for the first one-dimensional orthogonal transform in the block N
03, the reading order is the order shown in FIG.
The order of reading from the storage unit 103 for the second one-dimensional orthogonal transform in each orthogonal transform block is the order shown in FIG. The input block is a block N
In the first orthogonal transformation processing period of the block N, the signal line 115 by the selection unit 104
As shown in FIG. 8A, in the second orthogonal transformation period of the block N, the selected signal line 115
(B).

FIG. 7 shows another example of reading and writing of values in the storage unit 103 when the orthogonal transform block size n × n is 8 × 8 and the size of the current processing input block is 2 × 3 pixels. It is a figure explaining an order.

Assuming that the order shown in FIG. 7A is the input order of values in the unit of the orthogonal transformation block, the storage unit 1 for the first one-dimensional orthogonal transformation in the block N
03, the reading order is the order shown in FIG.
The order in which the result of the first one-dimensional orthogonal transformation is written back to the storage unit 103 is the order shown in FIG. Are read out in the order shown in FIG. At this time, the order is as described above because the horizontal pixel size of the input block <the vertical pixel size. Further, assuming that the input block is a block N, the signal line 115 by the selection unit 104 is connected to the signal line 115 in FIG.
As shown in FIG. 8C, during the second orthogonal transformation period of the block N, the signal line 115 by the selection unit 104 is also as shown in FIG.

As described above, according to the orthogonal transformation apparatus and method of the present embodiment, the selection unit 101 extracts blocks less than n × n pixels in units of n pixels in the horizontal or vertical direction. Control device 1
06, and can be controlled by the control device 106 to change the selection method when selectively extracting n pixels from the extracted pixel data. Two-dimensional orthogonal transform can be performed on blocks less than the number of blocks.

[0055]

As described above, according to the present invention, n
When performing an orthogonal transformation on a block less than × n pixels, redundancy in a processing period can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a two-dimensional orthogonal transform device according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of operation timing of the two-dimensional orthogonal transform device according to the embodiment of the present invention.

FIG. 3 is a diagram illustrating an example in which an input image is divided into blocks in units of orthogonal transformation.

FIG. 4 is a diagram illustrating a reading order of values in a storage unit 1 in a conventional example.

FIG. 5 is a storage unit 1 in a case where the orthogonal transform block size n × n is 8 × 8 and the size of the current processing input block is 2 × 8 pixels.
FIG. 11 is a diagram for explaining a reading and writing order of values at 03.

FIG. 6 shows a storage unit 1 in a case where the orthogonal transformation block size n × n is 8 × 8 and the size of the current processing input block is 8 × 2 pixels.
FIG. 11 is a diagram for explaining a reading and writing order of values at 03.

FIG. 7 is a storage unit 1 when the orthogonal transform block size n × n is 8 × 8 and the size of the current processing input block is 2 × 3 pixels.
FIG. 11 is a diagram for explaining the reading and writing order of values at 03.

FIG. 8 is a diagram illustrating a relationship between a signal line 114 and a signal line 115;

FIG. 9 is a diagram showing an example of operation timing of a conventional two-dimensional orthogonal transform device.

Claims (5)

[Claims] A first selection unit that selects one of image data input in units of n × n pixels and one-dimensional orthogonally transformed image data; and an image selected by the first selection unit. Storage means for storing data; extraction means for extracting image data stored in the storage means in units of n pixels in a horizontal or vertical direction; and selectively selecting n pixels from the pixel data extracted by the extraction means. Second selecting means for extracting, orthogonal transform means for performing one-dimensional orthogonal transform on the pixel data selectively extracted by the second selecting means, and for a block less than n × n pixels, Control means for changing the direction of extraction by the extracting means and controlling the selection method by the second selecting means. 2. A block having less than n × n pixels,
2. The orthogonal transformation device according to claim 1, wherein the orthogonal transformation device is a block located at an end of the image. 3. The image processing apparatus according to claim 1, wherein the second selection unit is configured to perform a first one-dimensional orthogonal transformation process when the horizontal direction of the image data is less than n pixels and a second one-dimensional orthogonal transformation process during the first one-dimensional orthogonal transformation process. In the processing, the horizontal direction is selected. If the vertical direction of the image data is less than n pixels, the horizontal direction is selected in the first one-dimensional orthogonal transformation process, and the second one-dimensional orthogonal transformation process is performed. The orthogonal transform apparatus according to claim 1, wherein a vertical direction is selected. 4. In a block having less than n × n pixels, the second selector compares the number of pixels in the horizontal direction with the number of pixels in the vertical direction of the block, and determines that the number of pixels in the horizontal direction is If the number of pixels is larger than the number of pixels in the first one-dimensional orthogonal transformation process, the horizontal direction is selected in the first one-dimensional orthogonal transformation process, and the vertical direction is selected in the second one-dimensional orthogonal transformation process. When the number of pixels is larger than the number of pixels in the horizontal direction, the vertical direction is selected in the first one-dimensional orthogonal transformation process, and the horizontal direction is selected in the second one-dimensional orthogonal transformation process. The orthogonal transform device according to claim 1. 5. A first selection step of selecting one of image data input in units of n × n pixels and one-dimensional orthogonally-transformed image data; and a selection step selected in the first selection step. A storage step of storing image data in a predetermined storage unit; an extraction step of extracting the image data stored in the predetermined storage unit in a horizontal or vertical direction in units of n pixels; and a pixel extracted in the extraction step. A second selection step of selectively extracting n pixels from the data, an orthogonal transformation step of performing one-dimensional orthogonal transformation on the pixel data selectively extracted by the second selection step, and n × n pixels A control step of changing the extraction direction in the extraction step for a block less than the number of blocks and controlling to change the selection method in the second selection step.