JP2006173993A - Image processing apparatus, method of controlling computer and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing apparatus which determines a system which decompresses compression image data and performs image decompression processing by not only the performance of the side which outputs and displays an image but also considering the information of the image itself. <P>SOLUTION: The image processing apparatus which can elongate the compressing image data includes an image resolution acquisition part 42 which acquires the resolution of the image from the compression image data, an image decompression system determination part 44 which determines the image decompression system by comparing the resolution of the image with the output performance value of the image processing apparatus, and an image decompression processor 46 which decompress the above compression image data by the system determined by the image decompression system determination part 44. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image processing apparatus, a computer control method, and a program, and more particularly to a technique for decompressing compressed image data.

2. Description of the Related Art Conventionally, in an image processing apparatus that decompresses compressed image data, the decompression method of the compressed image data is changed in accordance with the output-side performance (for example, the output resolution of a monitor) of the image processing apparatus that displays the decompressed image. There is something. For example, in Patent Document 1 below, it is assumed that the data truncation circuit truncates the high frequency component data of the DCT conversion coefficient when the monitor has a low resolution, and does not perform truncation when the monitor has a high resolution. When an image is displayed on the screen, the load of the image expansion process is reduced.
Japanese Patent Laid-Open No. 5-68235

  However, in the above-described prior art, it is determined whether or not to cut off the high frequency component of the compressed image data depending only on the output side performance of whether the monitor has a low resolution or a high resolution. That is, since the compression method of the compressed image data is switched without considering the information on the input side such as the attribute value of the original image (resolution, number of channels in the color space, etc.), for example, the monitor is assumed to have a high resolution However, the calculation time could not be shortened when the resolution of the original image was higher than that. Even if the monitor has a low resolution, if the resolution of the original image is lower than that, the image quality is reduced more than necessary.

  The present invention has been made in view of the above problems, and one of its purposes is to not only compress the image data in consideration of not only the performance of the image output and display side but also the information of the image itself. An object of the present invention is to provide an image processing apparatus, a computer control method, and a program for determining an expansion method and performing image expansion processing.

  In order to solve the above-described problems, an image processing apparatus according to the present invention is an image processing apparatus capable of decompressing compressed image data, the means for acquiring an attribute value of an image from the compressed image data, and the attribute of the image An image expansion method determining means for determining an image expansion method by comparing a value with an output performance value of the image processing apparatus, and a means for expanding the compressed image data by a method determined by the image expansion method determination means , Including.

  In addition, a control method of a computer according to the present invention (for example, a personal computer, a server computer, a printer, a multifunction peripheral, etc., the same applies hereinafter) includes a step of acquiring an attribute value of an image from compressed image data, An image expansion method determining step for determining an image expansion method by comparing the attribute value and the output performance value of the image processing apparatus; and a step of expanding the compressed image data by the method determined by the image expansion method determination step; , Including.

  The program according to the present invention also includes means for acquiring an attribute value of an image from compressed image data, and an image expansion method determination for determining an image expansion method by comparing the attribute value of the image with an output performance value of the image processing apparatus. And a program for causing a computer to function as means for decompressing the compressed image data by the method determined by the image expansion method determination means. The program may be stored in a CD-ROM (Compact Disk-Read Only Memory), a DVD-ROM (Digital Versatile Disk-Read Only Memory), a memory card, or any other computer-readable information storage medium.

  In the present invention, an attribute value of an image is acquired from the compressed image data, the image attribute value is compared with the output performance value of the image processing apparatus to determine an image expansion method, and the compressed image data is converted by the image expansion method. It extends. According to the present invention, the compressed image data can be decompressed by an appropriate image decompression method in consideration of both the attribute value of the image and the output performance value of the image processing apparatus.

  In one aspect of the present invention, the attribute value of the image is an image resolution, and the output performance value of the image processing apparatus is an output resolution. In this way, the compressed image data can be decompressed by an appropriate image decompression method by comparing the image resolution and the output resolution value of the image processing apparatus.

  In one aspect of the present invention, the compressed image data is compressed image data that has undergone orthogonal transform coding in units of a predetermined block, and the image expansion method determination unit compares the resolution of the image with the output resolution, and The number of pixels of the AC component per unit block used for decompressing the compressed image data is determined by comparing the quotient obtained by dividing the resolution of the image by the output resolution with the block size of the compressed image data. In this way, when decompressing the compressed image data, the calculation load can be reduced if the resolution of the image is larger than the output resolution, and more than necessary if the resolution of the image is less than or equal to the output resolution. It is possible to prevent the image quality from being degraded.

  In one aspect of the present invention, the attribute value of the image is the number of channels in the color space of the image, and the output performance value of the image processing device is the number of channels in the output color space. In this way, the compressed image data can be expanded by an appropriate image expansion method by comparing the number of channels in the color space of the image with the value of the number of channels in the output color space of the image processing apparatus.

  In one aspect of the present invention, the image expansion method determining means uses only a predetermined block of the compressed image data when the number of channels in the color space of the image is larger than the number of channels in the output color space. By so doing, it is possible to reduce the calculation load of the image expansion processing by discarding information that cannot be output depending on the image processing apparatus.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.

  FIG. 1 is a hardware configuration diagram of an image processing apparatus 10 according to an embodiment of the present invention. In the image processing apparatus 10 shown in the figure, a CPU (Central Processing Unit) 14, a RAM (Random Access Memory) 16, and an image output interface 18 are connected via a bus 12 so that mutual data communication is possible. The image output interface 18 is connected to the display 20.

  The CPU 14 controls each unit of the image processing apparatus 10 based on an operating system stored in a ROM (not shown). Similarly, the CPU 14 performs an operation of decompressing the compressed image data based on a program stored in a ROM (not shown). The bus 12 is for exchanging addresses and data between the units of the image processing apparatus 10. The RAM 16 stores compressed image data, but the compressed image data may be stored in a computer-readable storage medium. The RAM 16 is also used for the work of the CPU 14. The RAM 16 includes a VRAM (Video Random Access Memory). The output image data expanded by the CPU 14 is drawn on the VRAM, and the contents are displayed on the display 20 through the image output interface 18. Is output.

  FIG. 2 is a functional block diagram of the image processing apparatus 10. As shown in the figure, the image processing apparatus 10 functionally includes a header information analysis unit 40, an image resolution acquisition unit 42, an image expansion method determination unit 44, an image expansion processing unit 46, and an image output unit 48. It is comprised including. These are functions realized by executing a program stored in a ROM (not shown) in the image processing apparatus 10.

  The header information analysis unit 40 reads and analyzes the header information of the compressed image data 30 stored in the RAM 14. The header information of the compressed image data 30 stores, for example, the image resolution, the number of vertical pixels, the number of horizontal pixels, the number of channels in the color space, and other image attribute values. In this embodiment, the compressed image data is compressed by the JPEG (Joint Photographic Expert Group) method, which is a standard for image compression of still images, but other image compression methods may be used.

  The outline of the compression processing by the JPEG method is as follows. First, the RGB bitmap image is converted into a YUV bitmap image. Next, the YUV bitmap image is divided into pixel blocks composed of 8 × 8 pixels. Each pixel block is orthogonally transformed by DCT (Discrete Cosine Transform). As a result, each block of 8 × 8 pixels is converted into a frequency component block composed of 8 × 8 spatial frequency components. FIG. 3 shows a frequency component block orthogonally transformed by the above-described DCT. The upper left component in the figure is called a DC component, and the other portion is called an AC component. As shown in FIG. 4, the frequency characteristic of the frequency component block is such that the horizontal spatial frequency becomes higher as it goes from left to right, and the vertical spatial frequency becomes higher as it goes from top to bottom. The frequency increases from the upper left to the lower right. In general, human vision is insensitive to high-frequency components, so in JPEG compression, the high-frequency components are cut off to reduce the amount of data (quantization), and then Huffman coding is used to compress the data. ing. Here, one block is composed of 8 × 8 pixels. However, the number of pixels per block may be set to a predetermined number according to the number of pixels constituting the image data.

  The image resolution acquisition unit 42 acquires image attribute values from the compressed image data. Specifically, information representing the resolution of the image is acquired from the header information analyzed by the header information analysis unit 40. Here, if the resolution of the image is included in the header information, it is acquired, and even if it is not included, the image resolution is obtained by multiplying the number of vertical pixels and the number of horizontal pixels. To get.

  The image expansion method determining unit 44 determines the image expansion method by comparing the image attribute value (image resolution) with the output performance value of the image processing device (image processing device output resolution 32). Specifically, the unit used for decompressing the compressed image data by comparing the resolution of the image with the output resolution, and further comparing the quotient obtained by dividing the image resolution by the output resolution with the block size of the compressed image data. The number of AC component pixels per block is determined. Here, the block size is assumed to be block size = 8 × 8 when the predetermined block is composed of 8 × 8 pixels.

  Next, a method for determining the number of AC component pixels per block will be described. The CPU 14 compares the image resolution with the output resolution. Here, when the image resolution is higher than the output resolution, a quotient obtained by dividing the image resolution by the output resolution is obtained. The CPU 14 compares this quotient with the block size, and if this quotient is greater than or equal to the block size, it will discard all AC components. That is, in this case, the expansion process is performed only with the DC component. Hereinafter, this method is referred to as “extension method 1”. On the other hand, when the quotient obtained by dividing the image resolution by the output resolution is less than the block size, the number of pixels of the AC component is, for example, block size / (image resolution / output resolution) −1. That is, here, the number of pixels per block used for the decompression process is inversely proportional to the value of (image resolution / output resolution). Hereinafter, this method is referred to as “expansion method 2”. In this way, when the resolution of the image is larger than the output resolution, not all the information that the image has can be expressed in the output image, so all or some of the high frequency components of the AC component of the image can be represented. Truncate and extend. By doing so, it is possible to reduce the calculation load required for image expansion processing. Further, when the resolution of the image is equal to or lower than the output resolution, the decompression process is performed using the DC component and all AC components in order not to deteriorate the image quality. Hereinafter, this method is referred to as “extension method 3”.

  The image decompression processing unit 46 performs decompression processing of the compressed image by the compressed image decompression method determined by the image decompression method determining unit 44. Specifically, using the number of pixels of the AC component per unit block of the compressed image determined by the image expansion method determination unit 44, inverse DCT conversion processing was performed on each block, and the conversion processing was performed. The blocks are combined and the compressed image is decompressed.

  The image output unit 48 outputs and displays the image expanded by the image expansion processing 46 on the display 20 through the image output interface 18.

  Details of the operation of the image processing apparatus 10 will be described below.

  FIG. 5 is a flowchart showing image output processing in the image processing apparatus 10 according to the embodiment of the present invention. In this process, the header information of the compressed image data is analyzed (S101). Image resolution is acquired from the analyzed header information (S102). Further, when there is no image resolution in the header information, information on the resolution of the image such as the number of vertical and horizontal pixels of the image is acquired, and the image resolution is calculated. An image expansion method determination process is performed from the image resolution and the output resolution of the image processing apparatus (S103), and a compressed image expansion process is performed according to the determined method (S104). The image expansion method determination process and the compressed image expansion process will be described later. Then, the decompressed image is output and displayed on the display 20 through the image output interface 18 (S105).

  FIG. 6 is a flowchart showing the determination process of the image expansion method. In this process, it is determined whether or not the image resolution is larger than the output resolution (S201). If it is larger, it is further determined whether or not the quotient obtained by dividing the image resolution by the output resolution is equal to or larger than the block size of the compressed image. (S202). If it is determined that the block size is not smaller than 1, the expansion method is set to 1 (S203). Otherwise, the expansion method is set to 2 (S204). If it is determined in S201 that the image resolution is not larger than the output resolution, the expansion method is set to 3 (S205).

  FIG. 7 is a flowchart showing decompression processing of a compressed image. In this process, it is first determined what the expansion method is (S301). If the decompression method is 1, all the AC components of the compressed image data are discarded and the decompression process is performed (S302). If the expansion process is 2, a part of the high frequency component of the AC component is discarded and the expansion process is performed (S303). If the decompression process is 3, the decompression process is performed without truncating the AC component (S304). In S303, the number of AC components per pixel block used for the decompression process is assumed to be block size / (image resolution / output resolution) -1, and other AC components are discarded. Here, the number of AC component selection methods is selected in order from the low frequency component, and specifically, from the upper left in the order indicated by the dotted line in FIG. Then, using the AC component determined by the above processing, inverse DCT conversion processing is performed on each pixel block (S305), and each pixel block is synthesized (S306) to obtain an output image.

  According to the image processing apparatus 10 according to the embodiment of the present invention described above, a method for expanding compressed image data in consideration of not only the performance of the image output side but also the information of the image itself. Can be determined and image expansion processing can be performed.

  The present invention is not limited to the above embodiment.

  For example, in the above embodiment, the image expansion method is determined using the image resolution and the output resolution, but the image expansion method is determined from the number of channels in the color space of the compressed image data and the number of channels in the output color space. It is good. For example, when the color space of the compressed image data is CIE-Lab (number of channels = 3) and the output color space is binary black and white (number of channels = 1), each image of the compressed image data is used for image expansion processing. The calculation load can be reduced by using only the block corresponding to L (luminance) among the pixel blocks. As described above, when the number of channels in the color space of the image is larger than the number of channels in the output color space, the decompression process may be performed using only a predetermined block of the compressed image data to reduce the calculation load.

  In the above embodiment, an output image is generated using all pixel blocks. However, a method of skipping unnecessary pixel blocks and expanding a compressed image using only predetermined pixel blocks may be added. In this case, which block is used may be determined according to the value of block size / (image resolution / output resolution).

  In the above embodiment, the image expansion method is determined by using the image resolution and the output resolution. However, by comparing the number of vertical and horizontal pixels of the compressed image with the number of vertical and horizontal pixels in the output resolution. The image expansion method may be determined. That is, when the number of vertical pixels in the compressed image is larger than the number of vertical pixels in the output resolution, or when the number of horizontal pixels in the compressed image is larger than the number of horizontal pixels in the output resolution, the AC of the compressed image data You may make it extend | stretch by truncating a part or all high frequency component of a component. The number of vertical and horizontal pixels in the output resolution may be calculated from the vertical or horizontal length of an output medium such as paper or a display.

It is a hardware block diagram of the image processing apparatus which concerns on embodiment of this invention. It is a functional block diagram of an image processing apparatus. It is a figure which shows the frequency component block orthogonally transformed by DCT. It is a figure which shows the frequency characteristic of a frequency component block. It is a flowchart which shows the image output process in an image processing apparatus. It is a flowchart which shows the determination process of an image expansion system. It is a flowchart which shows the expansion process of a compressed image.

Explanation of symbols

10 image processing device, 12 bus, 14 CPU, 16 RAM, 18 image output interface, 20 display, 30 compressed image data, 32 image processing device output resolution, 40 header information analysis unit, 42 image resolution acquisition unit, 44 image expansion method A determination unit, an image expansion processing unit, and an image output unit.

Claims (7)

In an image processing apparatus capable of decompressing compressed image data,
Means for obtaining an attribute value of an image from the compressed image data;
An image expansion method determining means for determining an image expansion method by comparing the attribute value of the image and the output performance value of the image processing device;
Means for expanding the compressed image data according to a method determined by the image expansion method determining means;
An image processing apparatus comprising: The image processing apparatus according to claim 1.
The attribute value of the image is the resolution of the image,
The output performance value of the image processing apparatus is an output resolution.
An image processing apparatus. The image processing apparatus according to claim 2,
The compressed image data is compressed image data subjected to orthogonal transform coding in a predetermined block unit,
The image decompression method determining means is configured to compare the compressed image by comparing the resolution of the image with the output resolution, and comparing the quotient obtained by dividing the resolution of the image by the output resolution with the block size of the compressed image data. Determine the number of AC component pixels per unit block used for data decompression.
An image processing apparatus. The image processing apparatus according to claim 1.
The attribute value of the image is the number of channels in the color space of the image,
The output performance value of the image processing apparatus is the number of channels in the output color space.
An image processing apparatus. The image processing apparatus according to claim 4.
The image expansion method determining means uses only a predetermined block of the compressed image data when the number of channels in the color space of the image is larger than the number of channels in the output color space.
An image processing apparatus. Obtaining image attribute values from the compressed image data;
An image expansion method determination step for determining an image expansion method by comparing the attribute value of the image and the output performance value of the image processing apparatus;
Expanding the compressed image data according to the method determined by the image expansion method determination step;
A computer control method comprising: Means for obtaining image attribute values from compressed image data;
An image expansion method determining means for determining an image expansion method by comparing the attribute value of the image and the output performance value of the image processing apparatus; and
Means for expanding the compressed image data according to a method determined by the image expansion method determining means;
As a program to make the computer function.

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