JP4711879B2 - Image processing apparatus, image forming apparatus, computer program, recording medium, and image processing method - Google Patents

Description

  The present invention relates to an image processing apparatus that compresses an image and decompresses the compressed image, an image forming apparatus including the image processing apparatus, a computer program for realizing the image processing apparatus by a computer, and the computer program recorded therein. The present invention relates to a recording medium and an image processing method.

  When performing color image processing with a scanner or digital camera, the amount of image data is large, so conventionally compressed image data compressed by an irreversible compression method such as JPEG (Joint Photographic Experts Group) or JPEG2000 is used. Processing such as transfer of image data or storage of image data is performed.

  In these compression methods, the amount of data is reduced mainly by two methods of quantization and encoding. For example, in the case of the JPEG method, a discrete cosine transform (DCT) is performed on each pixel of an input image, and the pixel value is a frequency coefficient that is a coefficient for each frequency component of each basis function of frequency conversion. Convert to Quantization is an operation that approximates the transformed frequency coefficient. In the case of a general image, the absolute value of the frequency coefficient tends to be smaller as the higher order frequency component (high frequency component), and the human visual characteristics have a lower resolution for high frequency, Of the frequency coefficient, the low frequency component is finely quantized and the high frequency component is coarsely quantized to greatly reduce the amount of data.

  When a color image is encoded, it is encoded with a YCbCr (Y: luminance signal, Cb: color difference signal between Y component and B component, Cr: color difference signal between Y component and R component) signal rather than encoding with an RGB signal. Since the code amount is smaller when the signal is converted to the JPEG method, generally, a YCbCr signal is input as an input, and each signal element is divided into a plurality of blocks each having 8 elements in the horizontal direction and 8 elements in the vertical direction as one block. Divide the input image. After that, DCT is performed in units of one block, and each element of the frequency coefficient of 8 rows and 8 columns after DCT is similarly assigned to each of the corresponding quantization tables of a total of 64 quantization coefficients of 8 rows and 8 columns. It is quantized by dividing by elements. In the JPEG method, these 8 × 8 quantization tables determine the quantization characteristics. JPEG compressed image data is generated using the integer part (quantization index) of the quantized result.

  When decompressing the compressed image data, the quantization table used at the time of compression is used as an inverse quantization table, and the frequency coefficient is restored by inverse quantization that integrates each element of the inverse quantization table and the quantization index. In the JPEG method, the quantization table is added to the compressed image data in order to make the quantization table used for quantization coincide with the inverse quantization table used for inverse quantization during decompression. In the JPEG method, this inverse quantization table determines the inverse quantization characteristics. Thereafter, an inverse discrete cosine transform (IDCT) is performed to restore the YCbCr signal.

  In the JPEG2000 system, discrete wavelet transform (DWT) is used instead of DCT. In the JPEG2000 quantization, explicit quantization for performing quantization at a quantization step specified for each code block is performed on the frequency coefficient after DWT processing, and the bit plane after encoding is set to all values “0”. There are two types of quantization methods, post-quantization, which reduce the amount of data by rounding down as “not considered”. When explicit quantization is performed, a quantization step for each code block is recorded. When post-quantization is performed, information of bit planes regarded as “0” is recorded. In the JPEG2000 system, the quantization step for each code block and the bit plane selection method for performing “0” determination determine the quantization characteristics. When decompressing the compressed image data, the recorded information is referred to and the data decompression is performed. The quantization step for each recorded code block and the information of the bit plane regarded as “0” are inversely quantized. Determine characteristics.

  When printing an image on a printer or displaying it on the screen of a display device based on the compressed image data, after expanding the compressed image data, the resolution and image size when the expanded image data is printed or displayed on the screen Depending on the above, a scaling process is performed and printing or display is performed.

  For example, in a color copying machine or the like, when printing an entire view composed of a plurality of images acquired by a high-resolution scanner on one sheet of paper, or in a digital camera, the captured image data is small for review on the spot. In the case of displaying on a liquid crystal display device, it is necessary to perform reduction processing such as conversion from high resolution to low resolution and reduction of the image size.

  As a reduction processing method, a reduction processing method based on interpolation using a neighboring point using a reduction in the number of pixels by simple thinning, a bilinear method, a bicubic method, or the like is known. When performing a reduction process, if the expanded image contains a high-frequency component that cannot be expressed with the resolution after the reduction process, the reduction process causes aliasing moire (moire) that causes aliasing distortion. appear. In addition, when the printer or the display device has performed halftone gradation expression processing such as dithering, when a frequency component higher than the frequency represented by the dithering matrix is included in the image to be reduced Moire also occurs.

  Therefore, conventionally, in order to prevent the occurrence of moiré, a low-pass filter process corresponding to the scaling factor of the reduction process is performed on the expanded image to remove high frequency components.

  In addition, in order to reduce the occurrence of moiré, the image data captured by the image sensor is orthogonally transformed and quantized, and the inverse quantization is performed by making the quantization coefficient value smaller than the quantization coefficient at the time of inverse quantization. An apparatus for performing resolution conversion has been proposed (see Patent Document 1).

Also, the low frequency components are extracted from the frequency components of a specific image and compressed, and the remaining high frequency components are expressed based on the information related to the extracted low frequency components, and the low frequency components and the related information are synthesized. Thus, simple image data is generated. Proposed a method to extract low-frequency components from the generated simple image data, extract related information, decode high-frequency components based on the low-frequency components, and combine the low-frequency components and high-frequency components to restore the original image (See Patent Document 2).
JP-A-10-341369 JP 2000-299781 A

  However, the conventional method using the low-pass filter has a drawback that a large amount of processing time is required for the low-pass filter processing and resources such as an arithmetic circuit for performing the processing are required.

  The example of Patent Document 1 intends to simultaneously output an output image having an output resolution and an output image having a lower resolution than the output resolution, although low-pass filter processing can be reduced. Therefore, when performing a single image output in accordance with a predesignated output resolution, it is necessary to generate compressed image data having unnecessary frequency components even when it is known that resolution conversion is performed in advance. In order to store compressed image data, it is necessary to provide a large-capacity storage area.

  In the example of Patent Document 2, a low frequency component and a high frequency component are separated and handled separately, and then the separated low frequency component and high frequency component are synthesized to create simple image data. For this reason, it is necessary to perform the synthesis process even when printing at the same resolution that does not require a reduction process or when storing data in a memory card, which may increase the amount of processing.

The present invention has been made in view of such circumstances, and accepts an instruction to convert an expanded image to a low resolution or an instruction to reduce the image, and whether or not to save compressed image data obtained by compressing the image. Plural having different quantization coefficients for quantizing the frequency coefficient based on the conversion magnification of the resolution corresponding to the received designation or the reduction ratio of the image depending on whether to accept the designation and save the compressed image data By selecting one quantized information from the quantized information and quantizing the frequency coefficient using the selected quantized information, it is possible to suppress deterioration in image quality due to the occurrence of moire and improve the compression rate and necessary. it is possible to reduce the storage area, when using the compressed image data stored again, the desired conversion or image processing apparatus that can be associated to the reduction of the image to a low resolution, And to provide an image forming apparatus including an image processing apparatus, a computer program for realizing the image processing apparatus by a computer, the recording medium and image processing method recorded the computer program.

Another object of the present invention is to inversely quantize the quantized data based on the conversion magnification of the resolution corresponding to the received designation or the image reduction magnification, depending on whether or not to save the compressed image data. Therefore, by selecting one inverse quantization information from a plurality of inverse quantization information having different inverse quantization coefficients, by dequantizing the quantized data using the selected inverse quantization information and expanding the image, An image processing apparatus capable of suppressing deterioration in image quality due to occurrence of moiré, an image forming apparatus including the image processing apparatus, a computer program for realizing the image processing apparatus by a computer, a recording medium storing the computer program, and an image processing method It is to provide.

An image processing apparatus according to the present invention performs predetermined frequency conversion on each pixel of an image to convert a pixel value into a frequency coefficient, quantizes the converted frequency coefficient, and encodes quantized quantized data. In an image processing apparatus that compresses an image and expands the compressed image, the quantization coefficient corresponding to the high-frequency component is increased as the resolution conversion magnification or the image reduction magnification is decreased in order to quantize the frequency coefficient. Storage means for storing information, accepting means for accepting designation for converting an expanded image to a low resolution or for reducing the image, and conversion ratio of resolution corresponding to designation accepted by the accepting means or reduction ratio for image based on, comprising: a first selecting means for selecting the stored quantized information, and means for accepting a designation of whether to store compressed image data compressed image, the compressed image The first selecting means is configured to select the quantization information corresponding to the conversion magnification of the resolution or the reduction ratio of the image corresponding to the received designation. The first selection means is configured to select predetermined quantization information regardless of the resolution conversion magnification or the image reduction magnification when receiving an instruction to save image data. The frequency coefficient is quantized using the quantization information selected by the means.

The image processing apparatus according to the present invention stores a plurality of pieces of inverse quantization information having a smaller inverse quantization coefficient corresponding to a high frequency component as a resolution conversion magnification or an image reduction magnification is smaller in order to inverse quantize quantized data. Storage means and second selection means for selecting the stored inverse quantization information based on the resolution conversion magnification or the image reduction magnification corresponding to the designation received by the reception means, and storing the compressed image data The second selecting means is configured to select predetermined dequantization information regardless of the resolution conversion magnification or the image reduction magnification corresponding to the received designation, and the compressed image when receiving a designation to store data, the second selection means, Yes and configured to select the inverse quantization information corresponding to the reduction magnification of the conversion ratio or image of the resolution, the first Characterized in that is arranged to stretch the image by inverse quantizing the quantized data using the inverse quantization information selected by the selecting means.

  An image forming apparatus according to the present invention includes the image processing apparatus according to any one of the above-described present inventions, and forms an image expanded by the image processing apparatus.

A computer program according to the present invention performs a predetermined frequency conversion on each pixel of an image to convert a pixel value into a frequency coefficient, quantizes the converted frequency coefficient, and encodes the quantized quantized data. In a computer program for compressing an image and compressing the compressed image, the computer converts the decompressed image to a low resolution or a resolution conversion magnification or image corresponding to the specification to reduce the image. based on the reduction ratio, specified not to function as a first selecting means for selecting one of the quantization information from a plurality of quantization information with different quantization coefficients for quantizing, store the compressed image data frequency coefficients When the first selection means receives the conversion, the conversion ratio of the resolution or the reduction ratio of the image corresponding to the specification to convert or the specification to reduce The smaller the smaller the quantization information, the larger the quantization coefficient corresponding to the high frequency component is selected. When the designation to save the compressed image data is received, the first selecting means It is configured to select predetermined quantization information regardless of the reduction magnification of the image, and the computer further functions as means for quantizing the frequency coefficient using the selected quantization information. .

A computer program according to the present invention, the computer, on the basis of the reduction magnification of the corresponding resolution of the conversion ratio or image designation to specify or reduced to the transformation, different inverse quantization coefficients for inverse quantizing the quantized data to function from the inverse quantization information as a second selecting means for selecting one of the inverse quantization information having, when receiving a specification that does not store the compressed image data, the second selection means, designated for the conversion or It is configured to select predetermined inverse quantization information regardless of the conversion magnification of the resolution corresponding to the specification to reduce or the reduction magnification of the image, and when the designation to save the compressed image data is received, the second selection The means is configured to select inverse quantization information having a smaller inverse quantization coefficient corresponding to a high-frequency component as the resolution conversion magnification or the image reduction magnification is smaller. Ri, a computer, characterized in that to further function as a means for decompressing the image by inverse quantizing the quantized data using the inverse quantization information selected.

  A computer-readable recording medium according to the present invention records a computer program according to any one of the above-described present invention.

An image processing method according to the present invention performs predetermined frequency conversion on each pixel of an image to convert a pixel value into a frequency coefficient, quantizes the converted frequency coefficient, and encodes quantized quantized data. In an image processing method that compresses an image and expands the compressed image, the quantization coefficient corresponding to the high frequency component is increased as the resolution conversion magnification or the image reduction magnification is decreased in order to quantize the frequency coefficient. Stores information, accepts the designation to convert the decompressed image to low resolution or the designation to reduce the image, accepts the designation of whether to save the compressed image data obtained by compressing the image, and saves the compressed image data When the designation to not be accepted is received, the quantization information corresponding to the conversion magnification of the resolution or the reduction magnification of the image corresponding to the designation to convert or to reduce is selected, and the compressed image data is selected. When receiving a specification that exists, select the resolution predetermined quantization information regardless reduction magnification of conversion ratio or image, characterized by quantizing the frequency coefficients by using the selected quantization information.

The image processing method according to the present invention stores a plurality of pieces of inverse quantization information having a smaller inverse quantization coefficient corresponding to a high frequency component as a resolution conversion magnification or an image reduction magnification is smaller in order to inverse quantize quantized data. In addition, when an instruction not to save compressed image data is received, predetermined dequantization information is selected regardless of the conversion magnification of the resolution or the reduction ratio of the image corresponding to the conversion specification or the reduction specification, and the compressed image is selected. When designation to save data is accepted, the inverse quantization information corresponding to the resolution conversion magnification or the image reduction magnification is selected, and the quantized data is inversely quantized using the selected inverse quantization information to generate an image. It is characterized by extending.

In the present invention, a plurality of pieces of quantization information (for example, quantization tables) having different quantization coefficients are stored in order to quantize the frequency coefficients. The quantization table is, for example, an array of 8 rows and 8 columns, and has an upper left quantization coefficient for the frequency coefficient of the DC component and a quantization coefficient for the frequency coefficient of the high frequency component in the horizontal and vertical directions toward the lower right. . A plurality of quantization tables having different quantization coefficients corresponding to each frequency coefficient are stored. When specifying whether or not to save compressed image data obtained by compressing an image, and when receiving a specification for converting an expanded image to a low resolution or a specification for reducing the image, conversion of the resolution corresponding to the received specification One quantization table is selected from the stored quantization tables based on the magnification or the image reduction magnification.

For example, a quantization table having a larger quantization coefficient corresponding to a high-frequency component is selected as the resolution conversion magnification or the image reduction magnification is smaller. Pixel values (pixel luminance signals, color difference signals, etc.) are converted into frequency coefficients by predetermined frequency conversion (for example, discrete cosine conversion). When the converted frequency coefficient is divided by the quantization coefficient for quantization, a quantization table having a large quantization coefficient corresponding to the high frequency component is used to obtain a quantization index of the high frequency component (an integer resulting from the quantization). Part) becomes smaller, and the high-frequency components in the image are attenuated. As a result, the smaller the conversion magnification of the resolution or the reduction ratio of the image, the more moiré that occurs more conspicuously, thereby improving the image quality. In addition, when quantization is performed with a quantization coefficient having a value larger than the frequency coefficient, the quantization index is “0”. By using a quantization table having a large quantization coefficient corresponding to the high frequency component, a large number of high frequency components can be obtained. The quantization index becomes “0”, the code amount is reduced, and the compression rate is improved.
Specifically, when a designation not to store compressed image data is received, a quantization table corresponding to the resolution conversion magnification or the image reduction magnification is selected. For example, a quantization table having a larger quantization coefficient corresponding to a high-frequency component is selected as the resolution conversion magnification or the image reduction magnification is smaller. As a result, the smaller the conversion magnification of the resolution or the reduction ratio of the image, the more moiré that occurs more conspicuously, thereby improving the image quality. It is also possible to accept designation of whether or not to save the compressed image data, confirm that it is not necessary to save the compressed image data, and conversion resolutions of various resolutions or image reductions that can be designated by the user at a later date There is no need to refrain from the compression rate in order to correspond to the magnification, and the compression rate is improved and the necessary storage area is reduced.
In addition, when a designation to save the compressed image data is received, a predetermined quantization table is selected from the stored quantization tables. For example, a predetermined quantization table having the smallest quantization coefficient corresponding to the high-frequency component is selected from the stored quantization tables regardless of the designated resolution conversion magnification or image reduction magnification. As a result, when the stored compressed image data is used at a later date, it is possible to correspond to various resolution conversion magnifications or image reduction magnifications that can be designated by the user .

In the present invention, a plurality of dequantization information (for example, dequantization table) having different dequantization coefficients for dequantizing quantized data (for example, quantization index) is stored. The inverse quantization table is, for example, an array of 8 rows and 8 columns, similar to the quantization table. The upper left is the inverse quantization coefficient for the DC component frequency coefficient, and the lower right is the high-frequency component in both the horizontal and vertical directions. It has an inverse quantization coefficient for a frequency coefficient. A plurality of inverse quantization tables having different inverse quantization coefficients corresponding to each frequency coefficient are stored. When specifying whether or not to save compressed image data obtained by compressing an image, and when receiving a specification for converting an expanded image to a low resolution or a specification for reducing the image, conversion of the resolution corresponding to the received specification One inverse quantization table is selected from the stored inverse quantization tables based on the magnification or the image reduction magnification.

For example, an inverse quantization table having a smaller inverse quantization coefficient corresponding to a high-frequency component is selected as the resolution conversion magnification or the image reduction magnification is smaller. When the inverse quantization coefficient is added to the quantized data and inverse quantization is performed, by using an inverse quantization table having a small inverse quantization coefficient corresponding to the high frequency component, the restored frequency coefficient after the inverse quantization is When the frequency coefficient of the high frequency component is reduced and converted to a pixel value (pixel luminance signal, color difference signal, etc.) by inverse transformation of predetermined frequency transformation (for example, inverse discrete cosine transformation), the high frequency component in the image is attenuated. . As a result, the smaller the conversion magnification of the resolution or the reduction ratio of the image, the more moiré that occurs more conspicuously, thereby improving the image quality.
Specifically, when the designation not to save the compressed image data is received, a predetermined inverse quantization table is selected from the stored inverse quantization tables. For example, a predetermined inverse quantization table having the largest inverse quantization coefficient corresponding to the high-frequency component is selected from the stored inverse quantization tables regardless of the conversion resolution of the designated resolution or the image reduction magnification. As a result, the restoration amount of the high frequency component is changed according to the conversion magnification of the designated resolution or the reduction magnification of the image, and the deterioration in image quality due to the occurrence of moire in the image after scaling is suppressed.
When a designation for saving the compressed image data is received, an inverse quantization table corresponding to the resolution conversion magnification or the image reduction magnification is selected. For example, an inverse quantization table having a smaller inverse quantization coefficient corresponding to a high-frequency component is selected as the resolution conversion magnification or the image reduction magnification is smaller. As a result, the smaller the conversion magnification of the resolution or the reduction ratio of the image, the more moiré that occurs more conspicuously, thereby improving the image quality .

In the present invention, the designation of whether or not to save the compressed image data obtained by compressing the image is accepted, the designation for converting the decompressed image to low resolution or the designation for reducing the image is accepted, and the designation designated One quantization information is selected from a plurality of quantization information having different quantization coefficients in order to quantize the frequency coefficient based on the corresponding resolution conversion magnification or image reduction magnification, and the selected quantization information is selected. By using and quantizing the frequency coefficient, it is possible to suppress deterioration in image quality due to the occurrence of moire, improve the compression rate, and reduce the necessary storage area.
In addition, when a designation not to store compressed image data is accepted, quantization information corresponding to the resolution conversion magnification or image reduction magnification is selected, and the frequency coefficient is quantized using the selected quantization information. In addition, it is possible to suppress deterioration in image quality due to the occurrence of moire, improve the compression rate, and reduce the necessary storage area.
In addition, when the designation to save the compressed image data is accepted, the predetermined compressed information is selected, and the frequency coefficient is quantized using the selected quantized information, so that the saved compressed image data is used again. In this case, conversion to a desired low resolution or image reduction can be supported .

In the present invention, a plurality of dequantization information having different dequantization coefficients for dequantizing the quantized data based on the conversion magnification of the resolution or the image reduction magnification corresponding to the received designation. By selecting one inverse quantization information from the above, and dequantizing the quantized data using the selected inverse quantization information to expand the image, it is possible to suppress degradation in image quality due to the occurrence of moire.
In addition, when the designation not to save the compressed image data is accepted, the predetermined inverse quantization information is selected from the stored inverse quantization information, and the quantized data is inversely quantized using the selected inverse quantization information. By doing so, it is possible to suppress image quality deterioration due to the occurrence of moire.
In addition, when an instruction to save the compressed image data is received, the inverse quantization information corresponding to the resolution conversion magnification or the image reduction magnification is selected, and the quantized data is inversely quantized using the selected inverse quantization information. Therefore, it is possible to suppress deterioration in image quality due to the occurrence of moire.

  Hereinafter, the present invention will be described with reference to the drawings illustrating embodiments. FIG. 1 is a block diagram illustrating a configuration of an image forming apparatus 100 including an image processing apparatus according to the present invention. An image forming apparatus 100 (for example, a digital multi-function peripheral) includes an image input unit 1, an image processing unit 2 (image processing device), an image output unit 4 as an image forming unit, and the like. Image data of analog signals of RGB (R: red, G: green, B: blue) obtained by reading an original with the image input unit 1 is output to the image processing unit 2, and the image processing unit 2 performs a predetermined process. The process is performed and output to the image output unit 4 as a digital color signal of CMYeK (C: cyan, M: magenta, Ye: yellow, K: black).

  The image input unit 1 includes, for example, a CCD (Charged Coupled Device), reads a reflected light image from a document image as an RGB analog signal, and outputs the read RGB signal to the image processing unit 2. The image output unit 4 is a printer such as an electrophotographic system or an inkjet system that outputs image data of a document image onto a recording sheet. The image output unit 4 may be a display device such as a display.

  The digital multi-function peripheral according to the present invention stores once used image data in a data storage unit 27 described later, and is stored in the data storage unit 27 after the next time even if no image data is input from the image input unit 1. It has a function of generating image forming data using the obtained image data and outputting it to the image output unit 4.

  There are two types of storage of image data in the data storage unit 27: temporary storage for outputting a plurality of images, and permanent storage (storing) in anticipation of reuse at a later date. is there. The user can explicitly specify whether to save (permanently store) the image data. The user can store (save) the image data in the data storage unit 27 by designating “Filing valid”. In the digital multi-function peripheral of the present invention, the image data is temporarily stored in the data storage unit 27 even when the user does not designate “filing valid” (that is, “filing invalid”). Thereby, even when there is no image data input from the image input unit 1 a plurality of times, a plurality of image outputs can be realized using the image data stored in the data storage unit 27.

  The image processing unit 2 includes an A / D conversion unit 21, a shading correction unit 22, an input tone correction unit 23, a color space conversion unit 24, a quantization coefficient calculation unit 25, an image compression unit 26, a data storage unit 27, an inverse quantum A conversion coefficient calculation unit 28, an image expansion unit 29, a scaling processing unit 30, a color correction unit 31, a region separation processing unit 32, a black generation and under color removal unit 33, a spatial filter processing unit 34, and a halftone output tone processing unit 35 , An operation unit 36, a control unit 37, and the like.

  The operation unit 36 is a touch panel type operation panel, and includes various keys and switches that accept user operation designations, a liquid crystal display that displays information to be notified to the user, and the like. For example, the user's operation can be specified as a scaling factor in increments of 1% from 25% to 400% specified independently in the horizontal and vertical directions, whether data storage is necessary (effective filing Invalid), image data to be output, and the number of copies to be output. The user operation designation may include parameters for designating the operation of each processing unit in addition to the above. When the image output unit 4 is a display device, the user operation designation includes resolution conversion and the like. In addition, instead of the operation unit 36, when a digital multifunction peripheral is connected to an external device such as a personal computer via a network or the like, a configuration realized by an operation on the external device may be used. .

  The A / D conversion unit 21 converts the RGB reflectance signal (reflectance data) input from the image input unit 1 into a digital signal, and outputs the converted RGB reflectance signal to the shading correction unit 22.

  The shading correction unit 22 performs a shading correction process on the A / D converted reflectance signal. The shading correction process is performed to remove various distortions that occur in the image signal due to the configuration of the illumination system, the imaging system, and the imaging system of the image input unit 1. The shading correction unit 22 outputs the corrected reflectance signal to the input tone correction unit 23.

  The input tone correction unit 23 performs input tone correction processing on the reflectance signal that has been subjected to the shading correction processing. The input tone correction process is a process for converting the reflectance signal into a signal that can be easily handled by the image processing unit 2, such as a density signal. The input tone correction unit 23 may further perform color balance processing on the reflectance signal. The input tone correction unit 23 outputs the processed reflectance signal (RGB signal) to the color space conversion unit 24.

  The color space conversion unit 24 converts the RGB signal into a YCbCr (Y: luminance signal, Cb: b color difference signal, Cr: r color difference signal) signal so that the subsequent image compression unit 26 can easily perform the compression process.

  The quantization coefficient calculation unit 25 stores a plurality of quantization tables. As will be described later, when the image compression unit 26 compresses the image data, the quantization table converts the YCbCr signal by frequency conversion applied to the image data, for example, Discrete Cosine Transform (DCT). Used to quantize the frequency coefficient. The quantization coefficient calculation unit 25 is input based on the scaling factor independently specified for the horizontal direction and the vertical direction input from the operation unit 36 and the necessity of storing image data (validation / invalidity of filing). Then, one required quantization table is selected from the plurality of quantization tables, and the selected quantization table is output to the image compression unit 26.

  The image compression unit 26 performs a process of compressing image data using, for example, the JPEG method. The image compression unit 26 performs discrete cosine transform (frequency conversion) on the YCbCr signal (pixel value of the image data) input from the color space conversion unit 24 for each block composed of 8 × 8 pixels, for example. Discrete Cosine Transform (DCT) is applied to convert the pixel value into a frequency coefficient that is a coefficient for each frequency component of each basis function.

  The image compression unit 26 performs quantization processing on the converted frequency coefficient using the quantization table input from the quantization coefficient calculation unit 25. More specifically, the image compression unit 26 divides each coefficient of the frequency coefficient configured by the 8 × 8 array by each quantization coefficient of the quantization table configured by the 8 × 8 array. Approximate the converted frequency coefficient.

  The image compression unit 26 performs a predetermined encoding process (for example, run-length encoding, Huffman encoding, entropy encoding) on the quantized quantized data (quantization index that is an integer part of the quantized result). Image data is compressed, and the compressed image data is stored in the data storage unit 27.

  The data storage unit 27 includes a semiconductor memory or a hard disk drive (HDD), and stores compressed image data compressed by the image compression unit 26 and information related to user designation input from the operation unit 36.

  In addition, the data storage unit 27, based on the designation of the image data to be output from the user and the designation of the number of output copies, once if the number of output copies is “1”, and multiple times corresponding to the number of copies if the number of copies is plural. The target compressed image data and user designation are output to the subsequent processing unit. Further, among the user designations, the handling of the compressed image data stored in the data storage unit 27 and the user-designated retention period differs depending on the designation of whether or not to save data (validation / invalidity of filing). For example, when filing is set to be invalid, the compressed image data and user designation stored at the stage where the compressed image data and user designation to be output are output to the processing unit in the subsequent stage for the designated number of output copies. Erased. In addition, when filing is set to be effective, the compressed image data to be output and the user designation are stored in the data storage unit 27 as long as they are not explicitly erased by the user. Treated as static data. The permanent data in the data storage unit 27 outputs the compressed image data to be output and the user designation to the subsequent processing unit without the re-input of the image data from the image input unit 1 by the user designation from the operation unit 36. be able to.

  As will be described later, the inverse quantization coefficient calculation unit 28 performs inverse quantization on the quantized data obtained by decoding the encoded data when the image decompression unit 29 decompresses the compressed image data. A plurality of inverse quantization tables are stored. The inverse quantization coefficient calculation unit 28 performs image decompression based on the filing validity / invalidity included in the user designation output from the data storage unit 27 and the scaling factor designated independently in the horizontal and vertical directions. An inverse quantization table (for example, an inverse quantization table to be applied to a luminance signal, an inverse quantization table to be applied to an r color difference signal, and a b color difference signal) to be used sometimes is output to the image expansion unit 29.

  The image decompression unit 29 decodes the data output from the data storage unit 27, and converts the quantized data composed of the 8 × 8 array obtained by the decoding into the inverse quantum composed of the 8 × 8 array. Multiply by each inverse quantization coefficient of the quantization table to convert to a frequency coefficient.

  The image decompression unit 29 performs an inverse discrete cosine transform (IDCT), which is an inverse transform of the frequency transform, for each block composed of 8 × 8 pixels with respect to the transformed frequency coefficient, and YCbCr The image data composed of these signals is expanded.

  The scaling processing unit 30 performs scaling in the main scanning direction and sub-scanning direction on the YCbCr signal expanded by the image expansion unit 29, and changes the image resolution and image size.

  The color correction unit 31 converts the YCbCr signal into a CMYe (C: cyan, M: magenta, Ye: yellow) density signal, and the CMYe density for realizing color reproduction in the image output unit 4. Color correction processing is performed on the signal. Specifically, the color correction process is a process of removing color turbidity based on the spectral characteristics of CMYe toner and ink each containing an unnecessary absorption component from the CMYe density signal. The color correction unit 31 outputs the converted CMYe density signal to the region separation processing unit 32 and the black generation and under color removal unit 33.

  The region separation processing unit 32 performs region separation processing based on the CMYe density signal input from the color correction unit 31. The region separation processing unit 32 outputs the separation result to the black generation and under color removal unit 33, the spatial filter processing unit 34, and the halftone output tone processing unit 35.

  The black generation and under color removal unit 33 performs black generation processing for generating a black (K) color signal based on the CMYe color signal constituting the density signal input from the color correction unit 31. Further, the black generation and under color removal unit 33 performs under color removal processing on the CMYe color signal. The under color removal process is a process of obtaining a new CMYe color signal by subtracting the black color signal generated by the black generation process from the CMYe color signal. As a result of these processes, the CMYe density signal is converted into image data composed of CMYeK color signals.

  The spatial filter processing unit 34 performs spatial filter processing using a digital filter on the CMYeK image data obtained by the black generation and under color removal unit 33. As a result, the spatial frequency characteristic of the image is corrected, so that it is possible to prevent the image output from the image output unit 4 from being blurred or causing deterioration in graininess.

  The halftone output tone processing unit 35 performs tone correction processing and halftone generation processing on the CMYeK image data. The halftone generation process is a process for dividing an image into a plurality of pixels so that gradation can be reproduced. A binary or multi-value dither method, an error diffusion method, or the like can be used. Further, the halftone output gradation processing unit 35 may perform processing for converting the density value of the image data into a halftone dot area ratio that is a characteristic value of the image output unit 4. The halftone output gradation processing unit 35 outputs the processed CMYeK image data to the image output unit 4.

  The control unit 37 is configured by a CPU and controls each process of the image processing unit 2.

  Next, the quantization coefficient calculation unit 25 will be described more specifically. The quantization coefficient calculation unit 25 outputs a quantization table used at the time of image compression to the image compression unit 26. For example, JPEG compression processing requires a quantization table composed of a total of 64 quantization coefficients of 8 rows and 8 columns, one for the luminance signal, common to the r color difference signal and the b color difference signal. A total of two used quantization tables are output to the image compression unit 26.

  The quantization coefficient calculation unit 25 holds, for example, a total of nine quantization tables, one set for a luminance signal and one set commonly used for an r color difference signal and a b color difference signal. Select which set is appropriate for output to the image compression unit 26 according to the necessity of saving (validation / invalidity of filing), the horizontal scaling factor and the vertical scaling factor specified by the user. The selected quantization table is output to the image compression unit 26.

  FIG. 2 is an explanatory diagram illustrating an example of a quantization table for luminance signals, and FIG. 3 is an explanatory diagram illustrating an example of a quantization table for r color difference signals and b color difference signals. Each quantization table is an array of 8 rows and 8 columns, the quantization coefficient for the frequency coefficient of the DC component in the upper left, and the quantization for the frequency coefficient corresponding to the basis function having a higher frequency in the horizontal direction from the upper left to the right. Coefficient, quantization coefficient for the frequency coefficient corresponding to the basis function with high frequency in the vertical direction from the top left to the bottom, and the quantization coefficient for the frequency coefficient corresponding to the basis function with high frequency in the horizontal and vertical directions at the bottom right Have

  As shown in the figure, each of the quantization tables corresponds to, for example, three states of 34% or more and less than 50% and 50% or more when the scaling factor designation in the horizontal direction and vertical direction is 25% or more and less than 34% Thus, each of nine states, which is a combination of three states in the horizontal direction and three states in the vertical direction, has a different quantization coefficient. These quantization tables are set so that the quantization coefficient corresponding to the high frequency increases as the scaling factor decreases. Note that the conversion ratio is not limited to the scaling factor, and may be a resolution conversion rate.

  When the user designation acquired from the operation unit 36 indicates that data storage is not required (filing is set to invalid), the quantization coefficient calculation unit 25 acquires the user-specified horizontal direction and vertical direction acquired from the operation unit 36. Based on the scaling factor with respect to the direction, one of the nine quantization tables is selected and output to the image compression unit 26.

  Further, when the user designation acquired from the operation unit 36 requires data storage (when filing is set to be effective), the quantization coefficient calculation unit 25 and the horizontal scaling factor designated by the user and A predetermined quantization table is selected regardless of the vertical scaling factor. This predetermined quantization table is the same as the quantization table selected when the scaling factor in the horizontal direction and the vertical direction is 50% or more when filing is disabled. 2 and 3 are examples when the sampling ratio of the YCbCr signal at the time of compression is uniform.

  Next, the inverse quantization coefficient calculation unit 28 will be described more specifically. The inverse quantization coefficient calculation unit 28 outputs an inverse quantization table used at the time of image expansion to the image expansion unit 29. For example, in the decompression process of the JPEG system, an inverse quantization table composed of a total of 64 inverse quantization coefficients of 8 rows and 8 columns is required, one for the luminance signal, one for the r color difference signal, and the b color difference signal. A total of two inverse quantization tables used in common are output to the image expansion unit 29.

  The inverse quantization coefficient calculation unit 28 holds, for example, a total of nine sets of two inverse quantization tables, one for the luminance signal and one commonly used for the r color difference signal and the b color difference signal. Which set is appropriate to be output to the image decompression unit 29 in accordance with designation of necessity of data storage (validation / invalidity of filing), horizontal scaling factor and vertical scaling factor designated by the user The selected inverse quantization table is output to the image decompression unit 29.

  FIG. 4 is an explanatory diagram illustrating an example of a dequantization table for luminance signals, and FIG. 5 is an explanatory diagram illustrating an example of an inverse quantization table for r color difference signals and b color difference signals. Each of the inverse quantization tables is an array of 8 rows and 8 columns, with the inverse quantization coefficient corresponding to the frequency coefficient of the DC component at the upper left, and the frequency coefficient corresponding to the basis function having a higher frequency in the horizontal direction from the upper left to the right. Inverse quantization coefficient, as it goes from top left to bottom, the inverse quantization coefficient for the frequency coefficient corresponding to the basis function whose frequency is high in the vertical direction, and the frequency coefficient corresponding to the base function whose frequency is high in both the horizontal direction and the vertical direction at the bottom right With inverse quantization coefficients.

  As shown in the figure, each of the inverse quantization tables has, for example, three states of 34% or more and less than 50% and 50% or more when the scaling factors in the horizontal direction and the vertical direction are 25% or more and less than 34%, respectively. Correspondingly, each of 9 states, which is a combination of 3 states in the horizontal direction and 3 states in the vertical direction, has different inverse quantization coefficients. These inverse quantization tables are set so that the inverse quantization coefficient corresponding to the high frequency decreases as the scaling factor decreases. Note that the conversion ratio is not limited to the scaling factor, and may be a resolution conversion rate.

  When the user designation obtained from the operation unit 36 requires data storage (when filing is set to be effective), the inverse quantization coefficient calculation unit 28 determines the user-specified horizontal direction obtained from the operation unit 36 and Based on the scaling factor with respect to the vertical direction, one of the nine inverse quantization tables is selected and output to the image expansion unit 29.

  In addition, when the user designation acquired from the operation unit 36 indicates that data storage is unnecessary (filing is set to be invalid), the inverse quantization coefficient calculation unit 28 determines the horizontal scaling factor designated by the user. A predetermined inverse quantization table is selected regardless of the vertical scaling factor. The predetermined inverse quantization table is the same as the inverse quantization table selected when the scaling factor in the horizontal direction and the vertical direction is 50% or more when filing is enabled. . 4 and 5 are examples in which the sampling ratio of the YCbCr signal at the time of compression is equal.

  As shown in FIG. 2 and FIG. 4, the quantization coefficient of the quantization table for the luminance signal selected when the scaling factors in the horizontal direction and the vertical direction are 50% or more are respectively in the horizontal direction and the vertical direction. This is the same as the inverse quantization coefficient of the inverse quantization table for the luminance signal that is selected when the scaling factor is 50% or more. Also, as shown in FIGS. 3 and 5, the quantization coefficient of the quantization table for the r color difference signal and the b color difference signal selected when the scaling factors in the horizontal direction and the vertical direction are 50% or more are: This is the same as the inverse quantization coefficient of the inverse quantization table for the r color difference signal and the b color difference signal selected when the scaling ratio in the horizontal direction and the vertical direction is 50% or more.

  Next, image compression processing and decompression processing will be described. First, a case where data storage is not designated, that is, a case where filing is invalid will be described. The image processing unit 2 selects and uses a quantization table used for image compression from nine sets held by the quantization coefficient calculation unit 25 in accordance with the scaling factors in the horizontal direction and the vertical direction. . As shown in FIGS. 2 and 3, these quantization tables are set so that the quantization coefficient corresponding to the high frequency increases as the scaling factor decreases. For this reason, when the frequency coefficient after DCT is quantized, the quantized data in the high-frequency part becomes smaller than the quantized data on the DC component side when the horizontal and vertical scaling factors are small. .

  The inverse quantization table used for image expansion is a predetermined (constant) inverse quantization table regardless of the scaling factor in the horizontal direction and the vertical direction when data storage is not designated, that is, when filing is disabled. Therefore, the frequency coefficient restored by inverse quantization has a smaller value corresponding to the high frequency of the basis function of the DCT as the scaling factor is smaller than when the scaling factor is larger. As a result, when the variable magnification is small, the high frequency component in the image after the image expansion is attenuated.

  In scaling processing performed after image expansion, scaling is performed according to the respective scaling factors in the horizontal and vertical directions specified by the user. At this time, if the decompressed image data includes a high-frequency component that cannot be expressed by the resolution after the reduction process, aliasing moire (moire) due to aliasing distortion occurs in the reduction process. By selecting the quantization table to be used at the time according to the scaling factor in the horizontal and vertical directions, the high-frequency components that cannot be expressed with the reduced resolution included in the decompressed image data are attenuated. The occurrence of aliasing moire (moire) due to aliasing distortion is suppressed, and as a result, the image quality can be improved. Conventionally, it has been necessary to perform low-pass filter processing to attenuate the high-frequency component. In the present embodiment, attenuation of high frequency components can be realized without performing low pass filter processing, and image quality can be improved with relatively low resources.

  Next, an image compression process and an expansion process when data storage is designated, that is, when filing is valid will be described. The image processing unit 2 performs image compression by selecting a predetermined (constant) quantization table as a quantization table used for image compression, regardless of the scaling factors in the horizontal direction and the vertical direction. After that, the inverse quantization table used for image expansion is selected from 9 sets held by the inverse quantization coefficient calculation unit 28 according to the respective scaling factors in the horizontal direction and the vertical direction. use. As shown in FIGS. 4 and 5, the inverse quantization table shows that when the scaling factor is small, the corresponding inverse quantization coefficient is smaller as the basis function frequency is higher than when the scaling factor is large. Is set to For this reason, the restored frequency coefficient after inverse quantization has a smaller frequency coefficient in the high frequency part as the scaling factor is smaller. When the scaling factor is small, the inverse quantization coefficient of the inverse quantization table is set smaller in the high frequency part than the quantization coefficient of the quantization table at the time of image compression. The high frequency component in the later image is attenuated.

  In scaling processing performed after image expansion, scaling is performed according to the respective scaling factors in the horizontal and vertical directions specified by the user. At this time, if the decompressed image data includes a high-frequency component that cannot be expressed by the resolution after the reduction process, aliasing moire (moire) due to aliasing distortion occurs in the reduction process. By changing the inverse quantization table used in the image according to the scaling factor in the horizontal and vertical directions, the high-frequency components that cannot be expressed with the resolution after reduction included in the decompressed image data are attenuated. The occurrence of aliasing moire (moiré) due to aliasing distortion is suppressed, and image quality can be improved. Conventionally, it has been necessary to perform low-pass filter processing to attenuate the high-frequency component. In the present embodiment, attenuation of high frequency components can be realized without performing low pass filter processing, and image quality can be improved with relatively low resources.

  When data storage is not specified, that is, when filing is disabled, it is only necessary to be able to output an image based on user specification at the image input stage, so the smaller the required data storage area, the better . In this case, depending on the horizontal and vertical scaling factors specified by the user, the smaller the scaling factor, the larger the quantization factor used, thereby removing the high-frequency component and reducing the smaller quantization factor. A relatively large compression ratio can be achieved as compared with the case where it is used. As a result, there is an advantage that the capacity of the data storage area required when the scaling factor is small is reduced.

  On the other hand, if data storage is specified, that is, if filing is enabled, the image data to be stored in the data storage area is not only the scaling factor that is specified by the user at the image input stage, but also after the data is stored. It must be able to accommodate any scaling factor that can be specified at a later date. For this reason, when compressing the stored compressed image data again, it is possible to cope with the reduction of the desired image by compressing with the quantization table composed of the smallest quantization coefficient at the time of image compression.

  6 and 7 are flowcharts showing the procedure of the compression process and the expansion process of the image processing unit 2. The image processing unit 2 determines whether or not there is an operation from the user (S11). If there is no operation (NO in S11), the image processing unit 2 continues the process of step S11 and waits until there is an operation from the user.

  When there is an operation from the user (YES in S11), the image processing unit 2 accepts the designation of conversion to low resolution or image reduction (S12), the number of output copies of the output image, the data of the input image data The designation of necessity of storage is accepted (S13).

  The image processing unit 2 determines whether or not the filing output is specified (S14). When the filing output is not specified (NO in S14), the image processing unit 2 is based on the image data input from the image input unit 1 instead of the stored data. Then, image input processing (for example, shading correction, input tone correction, etc.) is performed (S15), and it is determined whether or not data storage is designated for the input image data (S16).

  When data storage is specified (YES in S16), the image processing unit 2 selects a predetermined quantization table (S17), and performs discrete cosine transform on the input image data (S19). When data storage is not designated (NO in S16), the image processing unit 2 selects a quantization table corresponding to the conversion magnification to low resolution or the image reduction magnification (magnification) (S18), and in step S19. Process.

  The image processing unit 2 quantizes the frequency coefficient converted by the discrete cosine transform (S20), encodes the quantized quantized data (S21), and stores the compressed image data that has been compressed (S22).

  The image processing unit 2 reads the stored compressed image data (S23), and determines whether data storage is designated (S24). When data storage is specified (YES in S24), the image processing unit 2 selects an inverse quantization table corresponding to the conversion ratio to low resolution or the image reduction ratio (magnification ratio) (S25), and the compressed image Data is decrypted (S27). When data storage is not designated (NO in S24), the image processing unit 2 selects a predetermined inverse quantization table (S26), and performs the process of step S27.

  The image processing unit 2 inversely quantizes the decoded data (S28), performs inverse discrete cosine transform on the frequency coefficient converted by the inverse quantization (S29), and performs image processing based on the decompressed image data. Output processing (for example, scaling processing, color correction processing, etc.) is performed (S30). On the other hand, when filing output is specified in step S14 (YES in S14), the image processing unit 2 continues the processing from step S23 onward, assuming that processing is performed based on the stored data.

  The image processing unit 2 determines whether or not the designated number of images have been output (S31). If the designated number of images have not been output (NO in S31), the processing from step S23 is continued. When the designated number of images have been output (YES in S31), the image processing unit 2 determines whether data storage is designated (S32). When data storage is not designated (NO in S32), the image processing unit 2 deletes the compressed image data (S33) and ends the process. If data storage is designated (YES in S32), the image processing unit 2 stores the stored compressed image data as it is and ends the process.

  As described above, in the present invention, based on the conversion magnification of the resolution or the reduction magnification of the image, one of the quantization tables having different quantization coefficients corresponding to the magnification is selected and the frequency is selected. By quantizing the coefficients, it is possible to suppress image quality degradation due to the occurrence of moire, improve the compression rate, and reduce the necessary storage area. Also, moiré is generated by selecting and dequantizing one of the inverse quantization tables having different inverse quantization coefficients corresponding to the variable magnification based on the resolution conversion magnification or the image reduction magnification. Image quality degradation due to

  In the present invention, when a designation not to save compressed image data is accepted (when filing is disabled), a compression table is selected according to the resolution conversion magnification or the image reduction magnification during compression. When compressing and decompressing, by selecting and decompressing a predetermined (constant) inverse quantization table, it is possible to suppress degradation in image quality due to the occurrence of moire, improve the compression rate, and reduce the required storage area. it can. In addition, when a designation to save compressed image data is accepted (when filing is enabled), a predetermined (constant) quantization table is selected and compressed during compression, and a resolution conversion magnification or image reduction is performed during expansion. By selecting and expanding the inverse quantization table according to the magnification, when the stored compressed image data is used again, it is possible to cope with conversion to a desired low resolution or image reduction and moire. The deterioration of image quality due to the occurrence of the

  In the above embodiment, when filing is disabled, a constant inverse quantization table is selected regardless of the horizontal and vertical scaling factors specified, and when filing is enabled, horizontal and vertical are selected. This is a configuration that selects a fixed quantization table regardless of the direction scaling factor, but is not limited to this, and even when filing is disabled, each scaling factor in the horizontal and vertical directions The inverse quantization table can be selected according to the designation, and even when filing is enabled, the quantization table can be selected according to the respective scaling factors in the horizontal direction and the vertical direction. This also makes it possible to select a set of inverse quantization tables or a set of quantization tables that can achieve the purpose of removing high-frequency components.

  In the above-described embodiment, the JPEG method is exemplified as the image compression and image expansion method. However, by converting the pixel value to the frequency coefficient for each frequency component of the basis function, and quantizing the frequency coefficient, In the case of the irreversible method for compressing the data amount, it can be applied to other image compression and image expansion methods. For example, the present invention can be applied to the JPEG2000 system. The frequency coefficient after DWT at the time of image compression can be explicitly quantized by a quantization step for each code block. This quantization step is applied to each of filing valid / invalid, horizontal and vertical directions. In accordance with the scaling factor specification, the quantization coefficient calculation unit selects the inverse quantization step to be used in the inverse quantization when expanding the image, the filing valid / invalid, horizontal and vertical scaling factors respectively. Depending on the designation, it can be selected by the inverse quantization coefficient calculator. Also, it can be applied to post-quantization in the JPEG2000 system. In this case, information on the bit plane that should be regarded as “0” when compressing the image is selected by the quantization coefficient calculation unit in accordance with the filing validity / invalidity and the horizontal and vertical scaling factors. Then, the information of the bit plane that should be regarded as “0” at the time of image expansion is selected by the inverse quantization coefficient calculation unit according to the filing validity / invalidity and the respective scaling factors in the horizontal direction and the vertical direction. be able to.

  In the above-described embodiment, the quantization coefficient of the quantization table, the inverse quantization coefficient of the inverse quantization table, the division of the scaling factor, and the like are examples, and are not limited thereto. Further, the number of quantization tables and inverse quantization tables held is not limited to nine.

  The present invention is not limited to application to signals converted from RGB to YCrCb, but can also be applied to signals converted from RGB to YIQ.

  In the above-described embodiment, as the image input unit 1, for example, a flat bed scanner, a film scanner, a digital camera, a mobile phone, or the like is used. Further, as the image output unit 4, for example, an image display device such as a CRT display or a liquid crystal display, an electrophotographic system or an ink jet system printer that outputs a processing result to a recording paper or the like is used. Further, the image forming apparatus 100 may include a modem as a communication unit for connecting to a server apparatus or the like via a network. Further, instead of acquiring the image data from the image input unit 1, the image data may be acquired from an external storage device, a server device, or the like via a network.

  The present invention relates to a computer program for performing processing for selecting an appropriate quantization table and inverse quantization table when compressing and expanding an image on a computer-readable recording medium on which a computer program to be executed by a computer is recorded. Can also be recorded. As a result, it is possible to provide a portable recording medium on which a computer program for performing the image processing is recorded. The recording medium may be a non-illustrated memory, for example, a program medium such as a ROM because processing is performed by a microcomputer, and a program reading device as an external storage device (not illustrated) is provided, and the recording medium is stored therein. It may be a program medium that can be read by being inserted. In any case, the stored computer program may be configured to be accessed and executed by the microprocessor, or the computer program read out may be a program (not shown) of the microcomputer. A method may be used in which the computer program is downloaded to the storage area and executed. In this case, it is assumed that the computer program for download is stored in the main device in advance. Here, the program medium is a recording medium configured to be separable from the main body, such as a tape system such as a magnetic tape or a cassette tape, a magnetic disk such as a flexible disk or a hard disk, and a CD-ROM / MO / MD / DVD. Semiconductors such as optical discs, IC cards (including memory cards) / optical cards, etc., or mask ROM, EPROM (Erasable Programmable Read Only Memory), EEPROM (Electrically Erasable Programmable Read Only Memory), flash ROM, etc. It may be a medium that carries a computer program fixedly including a memory. Further, in this case, since the system configuration is connectable to a communication network including the Internet, the medium may be a medium that fluidly carries the computer program so as to download the computer program from the communication network. When the computer program is downloaded from the communication network in this way, the computer program for download may be stored in the main device in advance or installed from another recording medium.

1 is a block diagram illustrating a configuration of an image forming apparatus including an image processing apparatus according to the present invention. It is explanatory drawing which shows an example of the quantization table for luminance signals. It is explanatory drawing which shows an example of the quantization table for r color difference signals and b color difference signals. It is explanatory drawing which shows an example of the dequantization table for luminance signals. It is explanatory drawing which shows an example of the inverse quantization table for r color difference signals and b color difference signals. It is a flowchart which shows the procedure of the compression process of an image process part, and an expansion process. It is a flowchart which shows the procedure of the compression process of an image process part, and an expansion process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image input part 2 Image processing part 4 Image output part 25 Quantization coefficient calculation part 26 Image compression part 27 Data storage part 28 Inverse quantization coefficient calculation part 29 Image expansion part 36 Operation part 37 Control part

Claims (8)

Performs a predetermined frequency conversion on each pixel of the image, converts the pixel value into a frequency coefficient, quantizes the converted frequency coefficient, encodes the quantized quantized data, compresses the image, and compresses the image In an image processing apparatus for decompressing
Storage means for storing a plurality of pieces of quantization information having a larger quantization coefficient corresponding to a high frequency component as a resolution conversion magnification or an image reduction magnification is smaller in order to quantize the frequency coefficient;
Accepting means for accepting designation for converting the decompressed image to low resolution or designation for reducing the image;
First selection means for selecting stored quantization information based on a conversion magnification of a resolution or an image reduction magnification corresponding to the designation received by the reception means ;
Means for accepting designation as to whether to save compressed image data obtained by compressing an image ,
When the designation not to store the compressed image data is received, the first selection unit is configured to select quantization information corresponding to the conversion magnification of the resolution or the image reduction magnification corresponding to the received designation,
The first selecting means is configured to select predetermined quantization information regardless of the resolution conversion magnification or the image reduction magnification when the designation to save the compressed image data is received ,
An image processing apparatus, wherein the frequency coefficient is quantized using the quantization information selected by the first selection means. Storage means for storing a plurality of inverse quantization information in which the inverse quantization coefficient corresponding to the high frequency component is smaller as the resolution conversion magnification or the image reduction magnification is smaller in order to inverse quantize the quantized data;
Second selection means for selecting the stored inverse quantization information based on the conversion magnification of the resolution or the image reduction magnification corresponding to the designation received by the reception means;
When the designation not to store the compressed image data is received, the second selection means is configured to select predetermined dequantization information regardless of the conversion ratio of the resolution or the reduction ratio of the image corresponding to the received designation. And
When the designation to save the compressed image data is received, the second selection means is configured to select inverse quantization information according to the resolution conversion magnification or the image reduction magnification,
The image processing apparatus according to claim 1, characterized in that is arranged to stretch the image by inverse quantizing the quantized data using the inverse quantization information selected by said second selection means. An image processing apparatus according to claim 1 or claim 2, the image forming apparatus, and forming a decompressed image in the image processing apparatus. The computer performs a predetermined frequency conversion on each pixel of the image, converts the pixel value into a frequency coefficient, quantizes the converted frequency coefficient, encodes the quantized quantized data, compresses the image, and compresses the image In a computer program for decompressing a recorded image,
A plurality of computers having different quantization coefficients for quantizing the frequency coefficient based on a conversion conversion factor of a resolution corresponding to a specification for converting an expanded image to a low resolution or a specification for reducing the image, or a reduction magnification of the image first selecting means and to thereby function to select one of the quantization information from the quantization information,
When the designation not to store the compressed image data is received, the first selection means determines the quantization coefficient corresponding to the high-frequency component as the conversion magnification of the resolution corresponding to the designation of conversion or the designation of reduction or the image reduction magnification is smaller. Is configured to select quantization information with a large
The first selecting means is configured to select predetermined quantization information regardless of the resolution conversion magnification or the image reduction magnification when the designation to save the compressed image data is received,
A computer program for causing a computer to further function as means for quantizing a frequency coefficient using selected quantization information. The computer, on the basis of the reduction magnification of the corresponding resolution of the conversion ratio or image designation to specify or reduced to convert, from the inverse quantization information having different inverse quantization coefficients for inverse quantizing the quantized data 1 One of the to to function second selecting means for selecting an inverse quantization information,
When a designation not to store compressed image data is received, the second selection means selects predetermined dequantization information regardless of the conversion magnification of the resolution or the reduction magnification of the image corresponding to the designation to convert or the designation to reduce Configured to
When the designation to save the compressed image data is received, the second selection unit selects the inverse quantization information having a smaller inverse quantization coefficient corresponding to the high frequency component as the conversion factor of the resolution or the reduction factor of the image is smaller. It is configured as
5. The computer program according to claim 4 , further causing the computer to function as means for dequantizing the quantized data using the selected dequantization information and decompressing the image. Recording medium readable on a computer, characterized in that are recorded thereon a computer program according to claim 4 or claim 5. Performs a predetermined frequency conversion on each pixel of the image, converts the pixel value into a frequency coefficient, quantizes the converted frequency coefficient, encodes the quantized quantized data, compresses the image, and compresses the image In an image processing method for decompressing
Frequency coefficients stores the plurality of quantization information quantization coefficient is large, corresponding to the high-frequency component as the reduction ratio of the resolution conversion magnification or image for quantizing is small,
Accepts a designation to convert the decompressed image to low resolution or a designation to reduce the image,
Accepts whether to save compressed image data compressed image,
When the designation not to save the compressed image data is received, the conversion information of the resolution corresponding to the designation to convert or the designation to reduce, or the quantization information according to the reduction magnification of the image,
When receiving the designation to save the compressed image data , select predetermined quantization information regardless of the conversion magnification of the resolution or the reduction magnification of the image ,
An image processing method characterized in that a frequency coefficient is quantized using selected quantization information. Stores the plurality of inverse quantization information dequantized coefficient smaller corresponding more to the high-frequency component reduction magnification of resolution conversion magnification or image is smaller for inversely quantizing quantized data,
When the designation not to save the compressed image data is received, the predetermined inverse quantization information is selected regardless of the conversion magnification of the resolution or the image reduction magnification corresponding to the designation to convert or the designation to reduce,
When receiving the designation to save the compressed image data , select the inverse quantization information according to the conversion magnification of the resolution or the reduction magnification of the image ,
The image processing method according to claim 7 , wherein the image is expanded by dequantizing the quantized data using the selected dequantization information.

Images