JP2007150537A - Image processor and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the number and capacity of a memory used for a process less than before when performing a process in which coded data are expanded by a coding method such as wavelet transformation to obtain the image of specified size. <P>SOLUTION: An expander 12 acquires hierarchy number (integer) i which satisfies both a highest hierarchy (i+1) of a specified image size or less and a lowest hierarchy (i) of a specified image size or larger, for the coded data stored in a storage 11. The expander 12, upon acquiring the hierarchy number i, applies hierarchies present from the top order hierarchy of the coded data to (i+1) hierarchy with an inverse wavelet transformation for expansion, and then reduces it. So, the page memory and line memory for expanding images are not required. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for obtaining an image of an arbitrary size from encoded data by an encoding method such as a wavelet transform.

  The hierarchical wavelet transform method is characterized in that low frequency components and high frequency components of image data are separated to generate encoded data composed of a plurality of layers. When an image of an arbitrary size is obtained from encoded data by this hierarchical wavelet transform method, image data belonging to all layers is expanded by inverse wavelet transform, and the expanded image data is converted into an image of a desired size. Follow the procedure of scaling. However, there is a problem that such expansion / magnification processing requires a considerable time.

Therefore, in Patent Document 1, wavelet transform coefficients (encoding) of layers existing from the highest layer corresponding to encoded data representing the image of the largest size to the hierarchy of the indirect layer +1 of the image size specified by the user. The size of (data) is determined as the image size of the expanded image. As a result, an expanded image closest to the image size specified by the user and smaller than the image size can be obtained. Therefore, the expanded image can be enlarged to the specified image size, and the processing time can be shortened. be able to.
JP 2002-344732 A

  However, in the method described in Patent Document 1, when expanding a decompressed image, there are a page memory for expanding pixels included in the image two-dimensionally and a line memory for expanding pixels one by one. Necessary. Therefore, there is a problem that the cost is increased and a space for mounting these memories is required.

  The present invention has been made in view of the above-described background, and in a process of expanding encoded data by a hierarchical encoding method such as wavelet transform to obtain an image of a specified size, a memory used for the process It is an object of the present invention to reduce the number or capacity of the above.

  In order to achieve the above object, the present invention provides a specifying means for specifying the size of an image, a storage means for storing encoded data constituted by a plurality of hierarchies, and a plurality of hierarchies constituting the encoded data. Among these, each layer from a layer corresponding to encoded data representing the image of the largest size to a layer corresponding to encoded data representing the image of the smallest size and larger than the size specified by the designating means. Decompression means for decompressing the encoded data to which it belongs to generate image data; and reduction means for reducing the image so that the image represented by the image data generated by the expansion means has a size designated by the designation means; And an output means for outputting the image reduced by the reduction means.

  According to this image processing apparatus, a code that represents an image of the smallest size that is greater than or equal to the specified size from the layer corresponding to the coded data representing the image of the largest size among the coded images of each layer. Since the encoded data belonging to each layer up to the layer corresponding to the digitized data is expanded and reduced, the page memory and line memory necessary for the image enlargement process are not required. Therefore, in the process of decompressing encoded data by a hierarchical encoding method such as wavelet transform to obtain an image of a specified size, the number or capacity of memories can be reduced more than before.

FIG. 1 is a diagram showing a configuration of an image processing apparatus 1 according to an embodiment of the present invention.
As illustrated in FIG. 1, the image processing apparatus 1 includes an image size designation unit 10, a storage unit 11, an expansion unit 12, a reduction unit 13, and an output unit 14. The image processing apparatus 1 may be built in an image forming apparatus that forms an image on a recording material based on image data, or may be a computer connected to the image forming apparatus, Alternatively, a stand-alone computer may be used.

  In FIG. 1, a storage unit 11 is, for example, a hard disk, and stores encoded image data (hereinafter referred to as encoded data). This encoded data is encoded by a hierarchical wavelet transform method and consists of a plurality of layers, and corresponds to a “wavelet transform coefficient” in the wavelet transform method. The image size designation unit 10 is an operator such as a keyboard or a mouse, for example, and the user can designate an arbitrary image size using the image size designation unit 10. The decompression unit 12 reads the encoded data from the storage unit 11 and decompresses it. The reduction unit 13 reduces the encoded data expanded by the expansion unit 12 so as to have the image size designated by the image size designation unit 10. The output unit 14 outputs the image data reduced by the reduction unit 13 to a display device that displays an image based on the image data, or outputs the image data to an image forming device that forms an image on a recording material based on the image data. .

Next, FIG. 2 is a flowchart showing a processing flow until the image processing apparatus 1 obtains an image (bitmap image) having a size designated by the user from the encoded data stored in the storage unit 11. In FIG. 2, first, the user designates a desired image size by the image size designation unit 10, and the image size designation unit 10 stores this size (step S1). The decompression unit 12 refers to each layer of the encoded data stored in the storage unit 11, and has a layer (i + 1) corresponding to the largest image that is equal to or smaller than the specified image size and equal to or larger than the specified image size. And the number of layers (integer value) i satisfying the layer (i) corresponding to the smallest image is obtained (step S2). That is, the decompression unit 12 obtains by calculation the integer i that satisfies (unencoded image ^{size) / 2 (i + 1)} ≦ designated image size <(before encoding image size) / 2 ^i.

  When the decompressing unit 12 obtains the number of layers i, the decompressing unit 12 performs inverse wavelet transform on the layers existing from the highest layer of the encoded data to the (i + 1) layer, and the decompressed image data (hereinafter referred to as decompressed image data). Obtain (step S3). In other words, the decompressing unit 12 encodes a code representing the smallest image that is equal to or larger than the specified size from the hierarchy corresponding to the coded data representing the largest image among the plurality of layers constituting the coded data. That is, the encoded image data belonging to each layer up to the layer corresponding to the encoded data is expanded to obtain expanded image data.

  Next, the reduction unit 13 reduces the image represented by the expanded image data to an image having a size designated by the image size designation unit 10 (step S4). As this image data reduction technique, a well-known technique can be applied. For example, the entire image may be reduced by thinning out pixels constituting the image. Such thinning-out processing only thins out pixels one after another according to a certain standard from image data, and does not require a large-capacity memory such as a page memory or a line memory.

  The reduction unit 13 may reduce the image size by a two-point interpolation method. The point-to-point interpolation method compares the position of the pixel before reduction (scaling) with the position where the pixel after reduction is to be placed, and determines the two pixels before reduction that sandwich the pixel after reduction. The density is inversely weighted according to the distance between the reduced pixel and these two pixels to determine the reduced pixel. FIG. 3 is a conceptual diagram for explaining this two-point interpolation method. In FIG. 3, for example, when attention is paid to the output pixel (pixel after reduction) DOUT1 located between the input pixels (pixels before reduction) DIN1 and DIN2, the density value of the output pixel DOUT1 is the density value of the input pixel DIN1 × ( 1−0.25) + the density value of the input pixel DIN2 × 0.25. Note that the distance between the output pixel DOUT1 and the input pixel DIN1: the distance between the output pixel DOUT1 and the input pixel DIN2 = 0.25: 0.75. Such a two-point interpolation method is realized by using a convolution calculator comprising a multiplier and an adder, and therefore does not require a large capacity memory such as a page memory or a line memory.

  In FIG. 2, the output unit 14 outputs the image data reduced by the reduction unit 13 to a display device or an image forming apparatus (not shown) (step S5).

  According to the embodiment described above, the layers existing from the highest layer of the hierarchical wavelet transform coefficient to the (i + 1) layer are expanded by inverse wavelet transform and then reduced to a specified image size. That is, since it is only necessary to reduce the expanded image, a relatively large capacity memory such as a page memory or a line memory necessary for the enlargement process is not necessary. Therefore, in the process of expanding the encoded data by a hierarchical encoding method called wavelet transform to obtain an image of a specified size, the number or capacity of memories can be reduced more than before.

The embodiment described above may be modified as follows.
The encoding method based on subband conversion is different from the above-described encoding method based on wavelet transform in that not only low frequency components but also high frequency components are sequentially decomposed in each layer. Therefore, even if subband transform is used instead of the wavelet transform used in the embodiment, an image having a specified size can be obtained by the same method as in the above embodiment.
A program capable of causing a computer to execute the functions of the expansion unit 12 and the reduction unit 13 related to the image processing described above can be written and distributed in a recording medium such as a magnetic medium, an optical recording medium, or a semiconductor memory. The computer reads the program recorded on the recording medium and executes the above-described operation according to the procedure. Alternatively, the program may be downloaded from a server connected to a network such as the Internet and installed on the image processing apparatus (computer).

1 is a block diagram illustrating a configuration of an image processing apparatus according to an embodiment of the present invention. 4 is a flowchart showing an execution procedure of the image processing apparatus according to the embodiment. It is a figure explaining a two-point interpolation method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image processing apparatus, 10 ... Image size designation | designated part, 11 ... Memory | storage part, 12 ... Expansion part, 13 ... Reduction part, 14 ... Output part.

Claims (3)

A specifying means for specifying the size of the image;
Storage means for storing encoded data composed of a plurality of hierarchies;
Encoded data that represents an image of the smallest size that is equal to or larger than the size specified by the specifying means, from the hierarchy corresponding to the encoded data that represents the image of the largest size among the multiple layers that constitute the encoded data Decompression means for decompressing encoded data belonging to each layer up to a layer corresponding to, and generating image data;
Reduction means for reducing the image so that the image represented by the image data generated by the expansion means has a size designated by the designation means;
An image processing apparatus comprising: output means for outputting an image reduced by the reduction means.   The image processing apparatus according to claim 1, wherein the encoded data is data obtained by encoding image data by a wavelet transform method or a subband transform method. Specifying the size of the image;
The encoded data constituted by a plurality of hierarchies is read out from the storage means, and among the plural hierarchies constituting the read encoded data, the specified above-mentioned hierarchy from the hierarchy corresponding to the encoded data representing the image of the largest size A step of generating image data by decompressing encoded data belonging to each layer up to a layer corresponding to encoded data that is equal to or larger than the size and represents the smallest image;
Reducing the image so that the image represented by the generated image data has the specified size;
And a step of outputting a reduced image.

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