JP2003178300A - Image processing method and image processor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To rotate an image by a small memory use quantity. <P>SOLUTION: An image storage space for storing an original image (a) is divided into square partial spaces having the prescribed size (b). Next, a partial image stored in the partial spaces is read out of the respective partial spaces, and rotational processing is individually applied, and the rotational processing- applied partial image is written in the partial space coincident in order on raster order on a memory with order on raster order in the image after rotating the partial image (c). When outputting the image after rotation, respective picture elements are read out and outputted in the order on the raster order in the image after rotating the picture elements from the image storage space (d and e). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotation processing technique for rotating an electronic image, and more particularly to a technique for reducing storage resources required for the rotation process.

[0002]

2. Description of the Related Art In a device for handling an electronic image, it is stored in a storage space which is a mapping of an electronic normal image space. In addition, this mapping is often performed by assigning each address in the image space to an X address in the image space as a lower address of the storage space and a Y address as an upper address of the storage space.

[0003] Then, the rotation processing of the image thus mapped in the storage space is performed in the simplest manner as follows.

[0004] That is, when rotating an image mapped in the storage space by 90 degrees as shown in FIG.
As shown in b, a storage space area corresponding to the image size obtained by rotating the image 90 degrees (clockwise direction) is secured as a storage destination of the rotated image. Then, each pixel of the original image in FIG. 7a is read in raster order, and this pixel is written to an address corresponding to the pixel position in the image after rotation in the newly secured storage space area shown in FIG. 7b. That is, in the illustrated 90-degree rotation example, the pixels read from the original image in FIG. 7a in raster order in which the rows (upper addresses) are advanced from top to bottom while the columns (lower addresses) are advanced from left to right for each row, In the newly reserved storage space area shown in FIG. 7b, the rows are written from top to bottom for each column while advancing the columns from right to left.

[0005]

According to the rotation processing shown in FIG. 7, at least a storage space for the area obtained by adding the area for the original image and the area of the image after rotation is required for the rotation processing. Becomes This has been a factor that hinders efficient use of storage resources.

[0006] Therefore, an object of the present invention is to realize a rotation process that can reduce the required storage resources.

[0007]

[Means for Solving the Problems] To achieve the above objects,
The present invention relates to an image processing apparatus that rotates an original image stored in a memory by a rotation angle that is an integral multiple of 90 degrees and outputs the rotated image as an image that is an area on the memory in which the original image is stored. The partial image stored in the partial space is read out from each of the partial spaces obtained by dividing the space into a plurality of parts each storing a partial image of a square shape, and the partial image stored in the partial space is rotated by the rotation angle. An on-memory rotation means for performing on-memory rotation processing for writing in the partial space above, and each pixel in the image space on the memory,
And a read output unit that performs a read output process of reading and outputting the pixel in an order determined according to the position of the pixel on the rotated image.

According to such an image processing device, the original image is
An order in which reading, rotation, and writing are performed in units of square partial images, and each pixel written back in the image space of the memory is determined according to the position of the previous pixel on the rotated image. The rotated image is output by reading and outputting with. According to such an image processing apparatus, for example, if reading, rotating, and writing are sequentially performed in units of a square partial image, the storage space other than the image space required for the above processing is temporarily stored. Therefore, a buffer memory for saving the capacity of one partial image for saving one partial image is sufficient. Therefore, such a rotation image processing device can be configured as a device that performs efficient image rotation processing using a small amount of storage resources.

[0009] Further, such a configuration of the image processing device that performs rotation in units of an image smaller than the original image is suitable for high-speed rotation processing in which a rotation calculation mechanism can be configured by small-scale hardware. It is a composition.

[0010] More specifically, for example, the above-described on-memory rotation processing, for example, a rotation buffer is provided, and one partial image is read from the partial space in the rotation buffer.
After that, if the partial space in which the partial image obtained by rotating the previously read partial image in the rotation buffer is to be written from the partial space has not yet read the partial image in the rotation buffer, from the partial space, If the partial space in which the partial image obtained by rotating the previously read partial image in the rotation buffer is to be written is the partial image already read from the partial space into the rotation buffer, the partial image is still in the rotation buffer. From the partial space in which the partial image that has not been read is read into the rotation buffer, and the partial image obtained by rotating the previously read partial image in the rotation buffer is written into the partial space in which the rotated partial image should be written. For all subspaces, read partial images from the subspace, By rotating the image obtained by rotating the partial image until it is written in the partial space where the rotated image is to be written, the rotation buffer for one partial image capacity is used, and the image on the memory is efficiently stored. It becomes possible to read, rotate, and write back each partial image from the space.

[0011] Further, for example, the on-memory rotation unit matches each of the partial images rotated by the rotation angle in the on-memory rotation process with a raster order of the partial image on the rotated image. If the subspace having the order on the image space in the raster order is written,
Correlation between the reading order according to the raster order in the rotated image of each pixel in the image space on the memory and the address order of each pixel in the image space on the memory in the reading and outputting process of the reading and outputting means. Therefore, the read address operation in the read output process can be simplified and speeded up.

[0012] Here, in the image processing apparatus as described above, a management unit that manages a rotation angle of a partial image on a partial space on the memory with respect to an original image as a total rotation angle is provided, and the on-memory rotation unit is provided. In the rotation processing on the memory, the order of the rotated partial image in the raster order on the rotated image, the position on the image space of the partial space from which the partial image is read, the rotation angle, and the memory Obtained according to the total rotation angle before the start of the upper rotation process, the read output means, in the read output process open,
The order of reading each pixel in the image space on the memory may be determined according to the total rotation angle at the start of the read output process. By doing so, it becomes possible to rotate the original image on the memory a plurality of times and output the rotated image at each rotation.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

First, the outline of the rotation processing according to the present embodiment will be described.

The rotation processing according to the present embodiment is performed at 90 degrees and 180 degrees.
It is applied to a rotation process that rotates in units of 90 degrees of 270 degrees and 270 degrees.

[0016] Then, the rotation process according to the present embodiment conceptually includes the following steps.

That is, first, the image storage area on the memory that stores the original image is divided into square partial spaces of a predetermined size.

Next, an image (hereinafter, referred to as a “partial image”) stored in each partial space is read out from each partial space, individually rotated, and the rotated partial images are rotated. The order in raster order obtained when the partial image is scanned in raster order in the subsequent image is obtained, and the partial image is stored in the obtained raster order and in the image storage space in which the original image is stored. The raster order obtained when the subspaces are scanned in the raster order is written in the subspaces that match each other.In the present embodiment, the raster order is defined as each position is advanced from the top to the bottom in the vertical direction. Regarding the position in the vertical direction, it indicates the scanning order in which the position in the horizontal direction is moved from left to right.

When outputting the image after rotation, each pixel is read out from the image storage space in the order of raster order in the image after rotation of the pixel and output.

A specific example of the above rotation processing will be described in detail with reference to the drawings.

[0021] Now, when rotating an image stored in the image storage space of horizontal and vertical 24 pixels x 16 pixels shown in Fig. 1a, first, this image storage space is each 8 pixels x 8 as shown in Fig. 1b. Divide into six square-sized subspaces of pixels. It should be noted that the numbers 1 to 6 and the directions thereof shown in each figure represent the identification of the partial images stored in each partial space before the rotation processing and the rotation angle with respect to the original image.
In addition, here, it is assumed that the pixel size of the original image can be fully divided into a plurality of square partial spaces.

Next, as shown in FIG. 1c, partial images are read out from each partial space, subjected to a rotation process corresponding to the rotation angle applied to the original image, and written in the partial space in the image storage space. The position of the subspace in which the partial image is written depends on the original image size and the rotation angle.The position in the raster order in the rotated image of the partial image and the raster order in the image storage space of the subspace in which the partial image is written The order of is determined so that they match.

[0023] For example, in the case of 90-degree rotation, the partial image 1 stored in the first partial space (upper left corner partial space) in the raster order of the image storage space before the rotation processing is rotated as shown in FIG. 1d. Since the order in the raster order in the subsequent image is 2, the data is written in the second partial space in the raster order in the image storage space (the second partial space from the upper left). On the other hand, in the case of the 180-degree rotation, the partial image 1 has the order of 6 in the raster order in the rotated image, and thus the sixth partial space in the raster order in the image storage space (the partial space at the lower right corner). Written in. Further, in the case of 270 ° rotation, the partial image 1 has the order of 5 in the raster order in the image after rotation, and thus the fifth partial space in the raster order in the image storage space (from the lower left to 2
Second subspace).

Then, when outputting the image after rotation, each pixel is read from the image storage space in the order of raster order in the image after rotation of the pixel and is output, and thus the image shown in FIG. The image after rotation is output.

[0025] By the way, the order of reading is such that when the original image is a square image and when the rotation angle is 180 degrees, the vertical and horizontal sizes of the original image and the rotated image match, so that the image storage is performed. The pixels may be read in raster order from space. On the other hand, when the original image is a square image and when the rotation angle is not 180 degrees, the partial images on the same row of the partial image in the rotated image are on different rows of the partial space in the image storage space. Therefore, if the pixels are read in raster order from the image storage space, the pixel reading order and the raster order of pixels in the rotated image will not match. Therefore, in such a case, as shown in an example in FIG. 1e, the order of reading each pixel from the image storage space in the order of raster order in the image after rotation of the pixel is from the image storage space. This is different from reading pixels in the order of raster order.

The outline of the image rotation processing according to the present embodiment has been described above.

An image processing apparatus that performs such image rotation processing will be described below.

FIG. 2 shows the configuration of the image processing apparatus according to this embodiment.

In the figure, the image processing unit 1 includes a memory 11,
Memory input / output control unit 12, rotation control unit 13, subspace access control unit 14, image management table 15, rotation buffer 17, rotation calculator 16, read address control unit 19
Have.

Then, the image processing unit 1 uses the image rotation request source 2
However, the image rotation processing is performed on the image written in the memory 11 via the memory input / output control unit 12, and the image output destination 3
Output to.

That is, when the image rotation request source 2 writes an image in the memory 11, the image rotation request source 2 performs the image rotation process on the memory 11.
The rotation processing unit is requested together with the notification of the image size and the rotation angle.

Upon receiving this request, the rotation control unit 13 of the rotation processing unit stores the notified image size and rotation angle in the image management table 15, and then first, on a memory as shown in FIG. 3a. Each part is controlled to perform the rotation process.

[0033] Note that FIG. 3a illustrates an example of the rotation processing procedure on the memory, in which the rotation image area is an area of horizontal and vertical pixels of 24 pixels × 16 pixels and the rotation angle is 90 degrees. It is shown. Reference numeral 30 in the drawing indicates the identification and rotation angle of the partial image stored in each partial space on the memory 11, and 31 indicates the identification and rotation angle of the partial image in the rotation buffer 17.

[0034] In the first cycle, first, the rotation control unit 13
Controls the subspace access control unit 14 and the memory input / output control unit 12, and divides the image storage area in the memory 11 as described above into a partial image of one of the square partial spaces. Control to read into the rotation buffer 17.

[0035] In the second cycle, the rotation control unit 13 rotates the rotation angle of the partial image stored in the rotation buffer 17 in the previous cycle by the rotation calculator 16, and the partial space access control unit 14 and the memory input / output control. The reading of the partial image from the partial space on the memory 11 into which the partial image read in the rotation buffer 17 in the previous cycle is written in the next cycle by the unit 12 is controlled. However, in the second step, if the partial space in the memory 11 into which the partial image read in the rotation buffer 17 in the cycle is written in the next third cycle has already been read in the rotation buffer 17 in the past, A partial image is read into the rotation buffer 17 from an arbitrary partial space which has not been read by the rotation buffer 17 in the past.

In the third cycle, the rotation control unit 13 controls the partial space access control unit 14 and the memory input / output control unit 12, and the partial image rotated by the rotation calculator 16 is rotated as described above. It controls writing to a partial space on the memory 11 that is determined according to the position on the image.

[0037] Then, in the same manner, the second cycle and the third cycle are repeated until the partial images of all the partial spaces are read out, rotated, and written back into the partial spaces.

[0038] Here, the above processing will be described in accordance with the example illustrated in FIG. 3A as follows.

[0039] First, the partial image 1 is read from the first partial space in the raster order to the rotation buffer 17 (a1).

Next, the partial image 2 is read from the second partial space in the raster order, which is the writing partial space after the rotation of the partial image 1, into the rotation buffer 17, and the previous rotation buffer 1 is also read.
The partial image 1 read in 7 is rotated 90 degrees and written in the second partial space in the raster order (a2).

[0041] Next, the partial image 4 is read from the fourth partial space in the raster order, which is the writing partial space after the rotation of the partial image 2, into the rotation buffer 17, and the previous rotation buffer 1 is also read.
The partial image 2 read in 7 is rotated by 90 degrees and written in the fourth partial space in the raster order (a3).

[0042] Next, the first partial space in the raster order, which is the writing partial space after the rotation of the partial image 4, is the already processed partial space, so the partial image 3 is rotated from the unprocessed partial space 3. At the same time as reading to the buffer 17, the partial image 4 previously read to the rotation buffer 17 is rotated by 90 degrees and written in the first partial space in the raster order (a4).

[0043] Next, the partial image 6 is read from the sixth partial space in the raster order, which is the writing partial space after the rotation of the partial image 3, into the rotation buffer 17, and the previous rotation buffer 1 is also read.
The partial image 3 read in No. 7 is rotated 90 degrees and written in the sixth partial space in the raster order (a5).

Next, the partial image 5 is read from the fifth partial space in the raster order, which is the writing partial space after the rotation of the partial image 6, into the rotation buffer 17, and the previous rotation buffer 1 is also read.
The partial image 6 read in 7 is rotated 90 degrees and written in the fifth partial space in the raster order (a6).

[0045] Finally, the partial image 5 read in the previous rotation buffer 17 is rotated by 90 degrees and written in the third partial space in the raster order (a7).

[0046] When the on-memory rotation process is completed as described above, the rotation control unit 13 performs the read output process.

In the read output process, the rotation control unit 13 causes the read address control unit 19 to read each pixel from the memory 11 according to the rotation angle and the image size stored in the image management table 15, as described above. Then, the pixels are read out in the order of raster order in the rotated image and output to the image output destination 3.

The image processing apparatus according to this embodiment has been described above.

By the way, in the above image processing device, when the image is a monochrome image with a pixel value of 1-bit expression, the partial space is 8 pixels × 8 pixels, and the memory 11 has a 64-bit data width, one part The partial image of the space can be read and written with one memory access.
By 6, the rotation processing can be realized as a circuit capable of high-speed rotation processing that simply replaces bits according to the rotation angle of 64 bits.

[0050] Hereinafter, an application example of the image processing unit 1 that performs the above-described rotation processing will be described.

FIG. 4 shows an example of application of the image processing unit 1 to a printer.

As shown in the figure, the printer 42 includes the host device 4
1, a host interface 43 that receives a print request in a predetermined printer language, a font memory 46 that stores a printer font that represents an image that represents characters and a font that is transferred from the host device, and analyzes the printer language to generate an image to be printed. Image generation unit 44, an output memory 45 for storing an image to be printed, a printer engine control unit 47 for controlling the printing operation of the printer engine 48 for the image stored in the output memory 45, and the image processing unit 1 according to the present embodiment. Have.

[0053] In such a configuration, the image generation unit 44
When it is necessary to generate an image in which a character is rotated based on the printer language, the image processing unit 1 reads the image of the character from the font memory 46 and sends the image to the image processing unit 1 to rotate the rotation process. Along with the designation of the angle and the area on the output memory 45 of the output destination, the image processing unit 1 is requested.
The image processing unit 1 requested to perform the rotation process performs the rotation process of the designated rotation angle on the character image as described above, and writes the image after the address rotation of the designated region of the output memory 45.

[0054] According to such a printer, it is possible to generate an image for printing including an image obtained by rotating the original character image at high speed by using less memory.

Here, the application of the image processing unit 1 to the rotation of the character image included in the image for printing is performed by the main image processing unit 1 to the printer driver that controls the printer on the host device.
Can also be performed by a form in which is applied as software.

Further, the image processing unit 1 can be applied as hardware or software to a device or an image processing application that performs general image processing as well as rotation of an image of characters printed by a printer.

That is, for example, by performing the output processing and the rotation processing of the image processing application on the electronic computer as the processing shown in FIG. 5, the main image processing unit 1 is a device that performs general image processing as software or image processing. Can be applied to applications.

The processing shown in FIG. 5 will be described below.

In this process, the image management table is used to manage the total rotation angle that is the total rotation angle from the original image.

[0060] As shown in the figure, in this process, when an output request for an image on the memory is made (step 51), the total rotation angle of the image is obtained by referring to the image management table, and according to the total rotation angle. The pixel reading order is determined (step 56), the above-mentioned reading output processing is performed, and an image is output (step 57).

On the other hand, when there is a rotation request for the image on the memory (step 52), first, the remainder of 360 degrees of the angle obtained by adding the requested rotation angle to the current total rotation angle is obtained in the image management table, Using this as a new total rotation angle, the total rotation angle is updated (step 53).

Then, the form of the rotation process is determined from the total rotation angle before the update and the required rotation angle (step 54),
The above-described on-memory rotation processing is performed on the image on the memory (step 55). When the on-memory rotation processing is completed, the total rotation angle of the image is obtained by referring to the image management table, and the total rotation The pixel reading order according to the angle is determined (step 56), the above-mentioned reading output processing is performed, and the image is output (step 58).

[0063] Here, the form of the rotation processing in step 54 and the pixel reading order in step 56 are determined as follows.

[0064] That is, for example, when the total rotation angle is 90 degrees and the image on the memory has been subjected to the rotation processing on the memory for the rotation angle of 90 degrees with respect to the original image, the rotation angle of 90 degrees is changed. If the rotation process is requested, the total rotation angle is updated to 180 degrees, and the pixel read order in the read output process is set to the same rotation angle 180 as the updated total rotation angle.
This is set to the same as when the rotation processing on the memory is performed as described above. On the other hand, the form of the on-memory rotation process is determined by a combination of the total rotation angle before updating and the rotation angle requested this time. As shown in FIG. 3b, which shows the procedure of the rotation processing on the memory when the rotation request of the rotation angle of 90 degrees is received in the state of the total rotation angle of 90 degrees, the rotation angle of the rotation processing for each partial image is requested (Fig. In the example of 90
This is the same as the rotation processing of the rotation angle of (degrees), but the partial space in which each partial image is written is when the partial image stored in the partial space has a total rotation angle of 0 degrees (before any rotation processing is performed. The partial image read out from the partial space stored in (1) is stored in the partial space when the in-memory rotation processing of the updated total rotation angle (180 degrees in the example in the figure) is performed as described above. Is obtained as the same subspace as.

[0065] As described above, by managing the total rotation angle of the image, the image rotation process can be repeatedly performed.

[0066] By the way, in the above description of the embodiments, the case where an image can be fully divided by a plurality of square subspaces has been described, but also in the case where an image cannot be sufficiently divided by a plurality of square subspaces,
The rotation processing according to this embodiment can be applied as follows.

[0067] That is, to the original image shown in Fig. 6a, dummy pixels whose area is indicated by a broken line are added to generate an image that can be fully divided by a plurality of square subspaces as shown in Fig. 6b. This image is subjected to on-memory rotation processing as shown in FIG. 6c. Then, in the read output process, each pixel is read in the order of the raster order on the rotated image while skipping the dummy pixel area shown in black in FIG. 6d, and the rotated image of FIG. 6e is read. Output.

The embodiments of the present invention have been described above.

[0069] As described above, according to the present embodiment, the rotation process can be realized by using the rotation buffer 17 having a capacity smaller than the storage capacity of the original image. Further, since the rotation processing is performed for each subspace, high-speed rotation processing can be performed by using an appropriate rotation calculator.

[0070]

As described above, according to the present invention, it is possible to realize the rotation processing which can reduce the required storage resources.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of image rotation processing according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an image processing apparatus according to an embodiment of the present invention.

FIG. 3 is a diagram showing an on-memory rotation processing example of the image processing unit according to the embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a printer according to an embodiment of the present invention.

FIG. 5 is a flowchart showing an image processing procedure according to the embodiment of the present invention.

FIG. 6 is a diagram showing an outline of image rotation processing according to the embodiment of the present invention.

FIG. 7 is a diagram illustrating a conventional image rotation processing example.

[Explanation of symbols]

1: image processing unit, 11: memory, 12: memory input / output control unit, 13: rotation control unit, 14: partial space access control unit, 15: image management table, 16: rotation calculator, 1
7: rotation buffer, 19: read address control unit, 4
1: host device, 42: printer, 43: host interface, 44: image generator, 45: output memory, 4
6: font memory, 47: printer engine control unit,
48: Printer engine

Continued front page    F term (reference) 2C087 AA11 AA17 AB05 BA03 BC03                       BD18 BD20                 5B057 CA08 CA12 CA16 CB08 CB12                       CB16 CC01 CD03 CH04                 5C073 AA04 BB02 BB07 BB09 CE04                 5C076 AA24 AA36 BA03 BA04

Claims (7)

[Claims] 1. An image processing apparatus for rotating an original image stored in a memory by a rotation angle of an integral multiple of 90 degrees and outputting the rotated image as a rotated image, the storage space on the memory storing the original image. From each of the partial space obtained by dividing the image space is divided into a plurality of parts that respectively store the partial image of the square shape, read the partial image stored in the partial space, and rotate the rotation angle, An on-memory rotation unit that performs an on-memory rotation process that writes exclusively to the partial space on the memory, and each pixel in the image space on the memory are determined according to the position of the pixel on the rotated image. An image processing apparatus comprising: a read output unit that performs a read output process of reading and outputting in order. 2. The image processing apparatus according to claim 1, wherein the on-memory rotation unit applies each of the partial images rotated by the rotation angle on the rotated image of the partial image in the on-memory rotation processing. Matches the order on the raster order of,
Writing into the partial space having an order in raster order on the image space, the read output means, in the read output processing, each pixel in the image space on the memory, on the rotated image of the pixel. An image processing method characterized by reading and outputting in raster order. 3. The image processing apparatus according to claim 2, further comprising: management means for managing, as a total rotation angle, a rotation angle of a partial image in a partial space on the memory with respect to an original image. The rotation means, in the rotation processing on the memory, the order in raster order of the rotated partial image on the rotated image, the position on the image space of the partial space from which the partial image is read, and the rotation angle, On the memory, the read output means obtains in accordance with the total rotation angle before the start of the rotation process, and the read output unit opens the read output process according to the total rotation angle at the start of the read output process on the memory. An image processing apparatus, characterized in that the order of reading each pixel in an image space is determined. 4. The image processing apparatus according to claim 1, further comprising a rotation buffer, wherein the on-memory rotation means is configured to rotate the on-memory rotation process from a partial space to the rotation buffer. When one partial image is read, and then the partial space in which the partial image obtained by rotating the previously read partial image in the rotation buffer is to be written is the one from which the partial space has not yet been read into the rotation buffer. If the partial space in which the partial image obtained by rotating the partial image previously read to the rotation buffer from the partial space should be written is the partial image already read from the partial space to the rotation buffer, the Read the partial image of this time from the partial space where the partial image is not read to the rotation buffer to the rotation buffer. At the same time, the process of writing the partial image obtained by rotating the previously read partial image in the rotation buffer to the partial space in which the rotated partial image should be written is performed by reading the partial image from the partial space for all the partial spaces. An image processing apparatus, characterized in that an image obtained by rotating a partial image is repeated until it is written in the partial space in which the rotated image is to be written. 5. A printer comprising an image processing apparatus according to claim 1, 2, 3 or 4, image generating means for generating an image to be printed, and printing means for printing the image generated by the image generating means. The image generation means, when generating the image to be printed, uses the image processing device to rotate a material image to be included in the image to be printed by rotating the image to be printed. Printer. 6. An image processing method for rotating an original image stored in a memory by a rotation angle of an integral multiple of 90 degrees and outputting the image as a rotated image, the method comprising: From a partial space obtained by dividing a certain image space into a plurality of parts each storing a square partial image, the partial image stored in the partial space is read out and rotated by the rotation angle, respectively. A rotation step on the memory for writing exclusively to the partial space on the memory, and a reading for reading out and outputting each pixel in the image space on the memory in an order determined according to the position of the pixel on the rotated image. And an output step. 7. A computer program read and executed by a computer, wherein the computer program causes the computer to rotate an original image stored in a memory by a rotation angle that is an integral multiple of 90 degrees. As a step for outputting as, the image space, which is an area on the memory in which the original image is stored, is divided into a plurality of parts each storing a square-shaped partial image, A sub-image rotation step of reading out a sub-image stored in the sub-space, rotating the rotation angle, and writing exclusively to the sub-space on the memory, and each pixel in the image space on the memory, , A read output step of reading and outputting in the order determined according to the position of the pixel on the rotated image. A computer program characterized by being executed.