Abstract:
Although dither processing is a high-speed process, it raises conflicts in improvement of resolution and improvement of tonality because of the structure of the dither matrix. Dither processing which is an image-matching-type is available to solve the above problem by analyzing frequency components in a partial area of an image, however, this method further causes a problem in long processing time. The present invention is provided to solve the above problems. When compressed image data  411  is expanded and processing to match an output device is performed, plural types of binarization processes are selectively utilized in accordance with the frequency component data of an image obtained at the time of the expansion process.

Description:
BACKGROUND OF THE INVENTION 
     Present invention relates to an image processing apparatus and method thereof and, more particularly, to an image processing apparatus and method for expanding coded image data and performing a process appropriate for the characteristics of an image, as well as a computer-readable memory. 
     Various methods have been suggested lately for realizing effective image compression by mapping an image in a frequency region and performing appropriate quantization and encoding for each frequency component. Particularly popular method of image compression is image-matching-type image compression which is a combination of discrete cosine transformation (DCT) and Huffman coding, and which is adopted as an international standard. The “image-matching-type image compression” performs image processing suitable for an image type (e.g., natural image, CG, character-oriented/line-oriented image or the like). Along with recent penetration of color image systems, such technique for image compression is often utilized for compressing a color image with high quality (high resolution). 
     Among the general color image systems, particularly, the wide-use of a color printing system adopting an ink-jet color printer is known. Such color image system often applies color printing operation where a high-resolution color image is compressed and stored in a disk device (file system), and the compressed data is expanded as necessary, resulting in rapid improvement in the color printing system. Since memory capacity of the file system is limited, image compression processing is essential to color image system so long as increase in memory capacity leads to increase in cost. 
     However, the above described technique raises the following problems. 
     One of the factors which determines quality of an output image in a color image system, including a binary color output device such as the above described ink-jet color printer or the like, is the method of processing full-color image data into pseudo half-tone image data, that is, a binarization method. 
     For binarization methods, a dither method, an error diffusion method and the like are available, each of which is utilized depending upon the desired image quality or the processing speed. Generally, the error diffusion method is used for generating a high quality (high resolution) image but notorious for long processing time. The dither method is capable of high-speed processing, but known to provide a problem of conflicts in improvement of resolution and improvement of tonality because of the structure of the dither matrix. Although an image-matching-type dither processing for analyzing frequency components in a partial area of an image is provided to solve the foregoing problem raised by the dither method, the problem of long processing time still remains. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in consideration of the above situation, and has as its object to solve the foregoing problems. 
     It is an object of the present invention to provide an image processing apparatus and method thereof which can obtain high-quality image data in a short period of time. 
     Particularly, it is an object of the present invention to perform resolution conversion or quantization processing in high quality and high speed. 
     According to the present invention, the foregoing object is attained by providing an image processing apparatus comprising: expansion means for expanding coded image data; storage means for storing data indicative of characteristics of an image obtained at the time of the expansion processing performed by said expansion means; first conversion means for performing resolution conversion on the image data, expanded by said expansion means, in accordance with the data indicative of the characteristics; and second conversion means for quantizing the image data, on which the resolution conversion is performed, in accordance with the data indicative of the characteristics. 
     Moreover, according to the present invention, the foregoing object is attained by providing an image processing apparatus comprising: expansion means for expanding coded image data; storage means for storing data indicative of characteristics of an image obtained at the time of the expansion processing performed by said expansion means; and process means for performing quantization processing on the image data expanded by said expansion means, in accordance with the data indicative of the characteristics. 
     Another object of the present invention is to perform color conversion processing in high quality and high speed. 
     According to the present invention, the foregoing object is attained by providing an image processing apparatus comprising: expansion means for expanding coded image data; storage means for storing data indicative of characteristics of an image obtained at the time of the expansion processing performed by said expansion means; and process means for performing color conversion processing on the image data expanded by said expansion means, in accordance with the data indicative of the characteristics. 
     Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
     FIG. 1 is a block diagram showing an image processing apparatus which can employ the present invention; 
     FIG. 2A is a block diagram showing a processing procedure for outputting compressed color image data to a color output device for outputting binary information; 
     FIG. 2B is a block diagram describing the process shown in FIG. 2A further in detail; 
     FIG. 3 is a conceptualized block diagram showing an image processing procedure in a color image system utilizing an application software; 
     FIG. 4 is a drawing showing a structure of a color printer which employs the present invention; 
     FIG. 5 is a block diagram showing overall image processing in the color image system according to a first embodiment of the present invention; 
     FIG. 6 is a functional block diagram showing processing in the color image system according to the present embodiment; 
     FIG. 7A is a graph for describing an example of interpolation methods  542  and  543  shown in FIG. 6; 
     FIG. 7B is a conceptualized diagram showing that interpolation methods applied to each of the blocks differ from each other by changing a method of interpolation; 
     FIG. 8A is a diagram showing an example of error conveying directions in binarization process; 
     FIG. 8B is a conceptualized diagram showing that binarization methods applied to each of the blocks differ from each other by changing a method of binarization; 
     FIG. 9 is a conceptualized block diagram showing image processing in the color image system of the present embodiment utilizing an application software; 
     FIG. 10 is a block diagram showing overall image processing in the color image system according to a second embodiment of the present invention; 
     FIG. 11 is a conceptualized diagram showing an example of binarization processing of compressed image data in the image processing apparatus according to the present embodiment; 
     FIG. 12A is a block diagram showing generation of low resolution image data based on compressed image data; 
     FIG. 12B is a view showing generation of low resolution image data based on compressed image data; 
     FIG. 13 is a conceptualized block diagram showing a structure of an image processing system according to a third embodiment of the present invention and a process of compressed image data being expanded, binarized and outputted; 
     FIG. 14 is a functional block diagram showing an example of image processing by a color image system according to a fourth embodiment of the present invention; 
     FIG. 15A is a diagram for explaining binarization processing utilized in the present embodiment; 
     FIG. 15B is a diagram showing generation of the most appropriate image in each block by a dither pattern being selected and combined by utilizing the binarization processing shown in FIG. 15A; 
     FIG. 16 is a chart showing how the time required for image-matching processing is reduced in the present embodiment; and 
     FIG. 17 is a diagram showing an example of a memory map in a memory medium storing program codes according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described in detail in accordance with the accompanying drawings. 
     The image data processing described below is realized by a CPU in a computer executing a processing program stored in a memory medium such as a ROM in a computer or a diskette, with the use of a work memory such as a RAM or the like. The processing described below can also be executed by supplying the foregoing processing program to a personal computer or a work-station comprising a CPU and a RAM, as a matter of course. 
     An example of an image processing apparatus which can employ the present invention is shown in FIG.  1 . 
     In FIG. 1, reference numeral  1  denotes a computer e.g. a personal computer, a work-station or the like;  2 , a display unit connectable to the computer  1 ;  3 , a printer unit connectable to the computer  1 ;  4 , a page memory for storing at least one page of uncompressed image data;  5 , a band memory for storing uncompressed image data for the number of lines corresponding to recording operation of the printer;  6 , a display interface for supplying image data to be displayed on the display unit  2 ;  7 , a CPU for executing operations that realize image processing described later;  8 , a RAM utilized as a work memory;  9 , a printer interface for supplying image data to the printer unit  3  to be printed;  10 , a ROM for storing programs or the like for enabling the CPU  7  to execute image processing which will be described later;  11 , a communication interface for performing communication with other computers or the like;  12 , hard disk for storing programs executed by the CPU and data utilized by the CPU; and  13 , a disk drive for inputting data stored in a removable memory medium  14 , e.g. CD ROM or the like, into the computer  1 . 
     &lt;Basic Image Processing&gt; 
     Basic image processing performed by a color image system according to the present invention will be now described. 
     Generally, when compressed color image data is to be outputted to a color output device for outputting binary information (e.g., ink-jet color printer, LED color printer or the like), expansion processing is first necessary to expand the compressed color image data, whereupon further processing is necessary, where a large amount of the expanded color data is temporarily stored in a file system or the like and binarization processing which will be described later is performed, to obtain an output image. FIG. 2A shows a processing procedure of outputting compressed color image data to a color output device for outputting binary information. Compressed data  111  denoting compressed color image data is restored into color image data  113  by expansion process  112 . The color image data  113  is then binarized for each of color components and the pseudo half-tone process is performed by a pseudo half-tone process  114 , thereafter transformed into binarized color image data  115 . 
     FIG. 2B describes the process shown in FIG. 2A further in detail. The compressed data  111 , expansion process  112 , color image data  113 , pseudo half-tone process  114 , binarized color image data  115  indicated in FIG. 2A respectively correspond with compressed data  219 , expansion process  220 , expansion data  231 , pseudo half-tone process  240  and binarized data  251  indicated in FIG.  2 B. 
     In FIG. 2B, original image data  211  indicative of color image data is transformed into frequency component data (orthogonal transformation coefficients) in a unit of 8×8 pixel blocks, for each color-component plane by a DCT transformation process  212 , and quantized as appropriate by a quantization process  213  for each of the frequency components. A DC coefficient indicative of the direct current component of the frequency component data is converted to a difference value between a preceding block and the succeeding block by utilizing a DC coefficient process  214 . An AC coefficient indicative of the alternating current component of the frequency component data is subjected to entropy encoding by an AC coefficient process  215 . A group of the above described data constitutes the compressed data  219 . 
     Note that the compressed data  219  may be generated by the CPU  7  of the computer  1  shown in FIG. 1, or may be supplied externally via the communication interface  11  or disk drive  13 . 
     The compressed data  219  obtained as a result of the foregoing series of processing is expanded as necessary and outputted. More particularly, an AC coefficient for quantization is obtained by performing entropy decoding in an AC coefficient process  221  included in the expansion process  220 , and a DC coefficient of a block of interest is obtained from a preceding block and a succeeding block, by utilizing an inverse DC coefficient process  222 . The expansion data  231  denoting color image data is obtained from a group of the quantization data obtained in the foregoing manner, by utilizing an inverse quantization process  223  and an inverse DCT transformation process  224 . 
     The expansion data  231  obtained in the above described manner is mapped (e.g. transformed from R, G and B data into Y, M, C and K data) in a color space suitable for printing by utilizing a color conversion process  232 , enlarged (or reduced) by resolution conversion process  241  to match with a print resolution, and transformed into binarized data  251  by an binarization process  242 . 
     FIG. 3 is a conceptualized diagram showing an image processing procedure in a color image system utilizing an application software. 
     In FIG. 3, a file operation menu (File-Menu)  310  in a window displayed on a display unit includes a file-open designation menu (FileOpen)  311  and a file-print designation menu (FilePrint)  312 . When the file open designation menu  311  is selected, a file-open dialogue (FileOpen)  313  is opened, and the designated file is loaded from a file system  321  (corresponding to hard disk in FIG. 1) by designating a file name listed in the dialogue. Note that when a file is loaded, a window  315  indicating an image of the file appears on the display unit  2 . 
     The process taking place inside the system is indicated by reference numeral  322  to  325  in FIG.  3 . That is, the designated file “file1.jpg” loaded from the file system  321  is expanded by an expansion module  322 , and the expanded image data is temporarily stored in a page memory  323  (corresponding to the page memory  4  in FIG.  1 ). The image data stored in the page memory  323  is reduced (or enlarged) by a resolution conversion module  324  to match with resolution of the display unit  2 , and the reduced (or enlarged) image data is displayed in the window  315  by a display module  325 . The foregoing processing is executed by the CPU  7 . 
     When the image data is to be printed, the image data is displayed by the operation described above, whereupon a user selects the file-open designation menu  312  to open a file-print dialogue (FilePrint)  314  on the display unit  2 . Since the dialog  314  indicates a currently-open file name, depressing an OK button will immediately start printing operation of the image data (which has been expanded and stored in the page memory  323 ) corresponding to the open file. 
     The process taking place inside the system is indicated by reference numeral  322  to  327 . That is, the image data expanded and stored temporarily in the page memory  323  in the above described processing is enlarged (or reduced) by the resolution conversion module  324  to match with print resolution of a printer, binarized for each color component by a pseudo half-tone processing module  326  and stored in a band memory  327  (corresponding to the band memory  5  in FIG.  1 ). The image data stored in the band memory  327  is sequentially transmitted to an interface unit  331  in a printer unit  330  (corresponding to the printer unit  3  in FIG. 1) by an interface unit  328  (corresponding to the printer interface  9  in FIG.  1 ), and stored in a band memory  332  by the interface unit  331 . A printer engine  333  prints a color image print  341  by reading out the image data from the band memory  332  as necessary. 
     In the above described color image system, a binarization method utilized in the pseudo half-tone process  114  in FIG. 2A or in the binarization process  242  in FIG. 2B or in the pseudo half-tone processing module  326  in FIG. 3 would become the main factor to decide quality of an output image. 
     &lt;Color Printer&gt; 
     FIG. 4 is a schematic view showing a structure of a color printer (corresponding to the printer unit  3  in FIG. 1) which employs the present invention. 
     In FIG. 4, reference numeral  2200  to  2230  denote color ink cartridges each of which is filled with yellow ink (Y), magenta ink (M), cyan ink (C) and black ink (K) respectively. Each of the ink cartridge and a pressure pump  2160  are independently connected with a pipe for supplying ink so that each of the color ink is sent from the pressure pump  2160  to the printhead  2120  with a fixed pressure. 
     A recording sheet is supplied from the rear portion of the color printer  2010  being held with a platen  2110  and a front guide roller  2150 . 
     The operation of the color printer  2010  is performed by depressing keys on a control panel  2180 , and a control board  2190  controls all the operation taking place in the color printer  2010 . 
     When printing operation is to be performed by the color printer  2010 , a print control command and data to be printed are sent to the control board  2190  via an interface (not shown). For instance, assuming R, G and B are designated in a color designation command, the control board  2190  which has received the print control command and print data, converts the R, G and B data to Y, M, C and K data and drives the printhead  2120  for printing. 
     Hereinafter, an image processing apparatus according to the present invention will be described in detail with reference to the accompanying drawings. 
     [First Embodiment] 
     &lt;Overall Processing&gt; 
     Overall image processing in a color image system of the first embodiment according to the present invention will be described. 
     According to image processing of the first embodiment, when a compressed image is expanded and binarized, frequency component data generated at the time of image compression is utilized as a reference in binarization processing, thereby achieving high quality and high speed image outputting. 
     FIG. 5 shows overall image processing performed by the color system of the first embodiment. Compressed data  411  indicative of compressed color image data is restored into color image data  413  by an expansion process  412 , and frequency component data  415  is generated. The frequency component data  415  is input to a unit executing an analyzing process  421 , and a binarization process  422  or a binarization process  423  is selectively performed for a specified region (block or the like) in accordance with the analysis result. 
     By virtue of the binarization process selected as appropriate in the above manner, the most appropriate processing for each region is performed on the restored color image data  413 . The image data being processed in a unit of a region is combined by a combine process  424 , and outputted as binarized color image data  425  corresponding to one page. 
     FIG. 6 is a functional block diagram showing an example of processing performed by the color image system according to the present embodiment, and illustrating the procedure of input color image data being compressed, binarized and output. 
     In FIG. 6, original image data  511  where each of the color components has 8 bit is transformed into frequency component data in a unit of, for instance, 4×4 pixel blocks, for each color-component plane, by a DCT transformation process  512 . Assuming that a function indicating the original image is i(x, y) and a corresponding DCT function is I(u, v), the transformation equation can be defined as follows:                I        (     u   ,   v     )       =         2        c        (   u   )         N            2        c        (   v   )         N            ∑     x   =   0     N            ∑     y   =   0     N              i        (     x   ,   y     )       ·   cos            {       (       2      x     +   1     )        u                   π   /   2        N     }     ·   cos          {       (       2      y     +   1     )        v                   π   /   2        N     }                     (   1   )                                
     where 
     0≦u,v≦N−1 
     c(u)=c(v)=1{square root over (2)}where u,v=0 
     c(u)=c(v)=1 where u,v=1,2, . . . , N−1 
     Next, the data is quantized for each of the frequency components by a quantization process  513 . Note the quantization process includes scaling where, for example, 8 bit are quantized to 4 bit. A DC coefficient indicative of the direct current component of the frequency component data is converted to a difference value between a preceding block and the succeeding block by utilizing a DC coefficient process  514 . An AC coefficient indicative of the alternating current component of the frequency component data is subjected to entropy encoding by an AC coefficient process  515 . A group of the above described data constitutes compressed data  519 . 
     The compressed data  519  obtained in the foregoing process is stored in a memory device, or expanded, or output, as necessary. The expansion process is now described in detail. 
     The compressed data  519  input into a unit executing an expansion process  520  is subjected to entropy decoding by an inverse AC coefficient process  521  to obtain a quantization AC coefficient. A DC coefficient of a block of interest is then obtained by an inverse DC coefficient process  522  on the basis of a difference value of a preceding block and the succeeding block. A group of quantization data is inversely quantized (or inversely scaled) by an inverse quantization process  523 . A resultant frequency component for each region is outputted to a file as an image frequency component  533 . The group of frequency component data obtained by the inverse quantization processing is mapped in a spatial region by an inverse DCT transformation process  524  and expansion data  531  indicative of color image data is obtained. 
     The expansion data  531  obtained in the foregoing manner is mapped in, for instance, a color space (e.g., from a space for R, G and B colors to a space for Y, M, C, and K colors) suitable for printing by a color conversion process  532 , enlarged (or reduced) to match with e.g., a print resolution, by a resolution conversion process  541 , and transformed into binarized data  551  indicative of pseudo half-tone color image data by binarization process  545 . At this point, the resolution conversion process  541  and the binarization process  545 , which performs density-preserving type quantization processing, change an interpolation method and a binarization method for each region in accordance with the image frequency component data  533 . 
     If a memory (RAM  8 ) utilized for image processing is large enough, the speed of the image processing can be increased by storing the image frequency component  533  in the memory. 
     &lt;Changing of Interpolation Method&gt; 
     Next, changing of an interpolation method in the resolution conversion process  541  will be described. 
     Values Ilow and Imid defined in the following equation are calculated utilizing the above described image frequency component  533  (I(u,v)) in each block and weight coefficients W00 to W33 obtained as appropriately by a visual experiment. 
     
       
           Ilow=W 00 ·I (0,0)+ W 01 ·I (0,1)+ W 10 ·I (1,0)+ W 11 ·I (1,1)+ W 22 ·I (2,2)+ W 33· I (3,3)  (2)  
       
     
     
       
           Imid=W   02   ·I (0,2)+ W 12 ·I (1,2)+ W 03 ·I (0,3)+ W 13 ·I (1,3)+ W 20 ·I (2,0)+ W 30· I (3,0)+ W 21· I (2,1)+ W 31 ·I (3,1)+ W 32 ·I (3,2)+ W 23 ·I (2,3)  (3)  
       
     
     Comparing the two values Ilow and Imid, the state of an image in a subject block is estimated on the basis of its value. For instance, if Ilow≦Imid, it is determined that there is a sharp variance in a horizontal direction or a vertical direction in the image, therefore an interpolation method  542  is utilized to obtain a sharp image. Meanwhile, if Ilow&gt;Imid, it is determined that there is no sharp variance such as an edge or the like in the image, therefore an interpolation method  543  is utilized so that the tone of an entire image smoothly varies. 
     FIG. 7A shows an example of the interpolation methods  542  and  543 . The interpolation method  542  adopts a method (Nearest Neighbor) where a value of a neighboring pixel indicated by  is utilized as an interpolation pixel indicated by ◯. The interpolation method  543  adopts a method (linear approximation) where a value for pixel interpolation is obtained by linear approximation of a neighboring pixel value. 
     FIG. 7B is a conceptualized diagram illustrating that an interpolation method applied for each block is different by changing interpolation methods, wherein the interpolation method  542  is applied for the image blocks  12  and  21 , and the interpolation method  543  is applied for the blocks  11 ,  13 ,  22  and  23 . 
     &lt;Changing of Binarization Method&gt; 
     Next, changing of a binarization method in the binarization process  545  will be described. 
     In the binarization process  545 , a direct current component I(0,0) of the image frequency component  533  is referred to, and if a block of interest is a monotone block, a dither pattern  546  is selected, otherwise an error diffusion  547  is selected. 
     FIG. 8B is a conceptualized diagram illustrating that a binarization method applied for each block is different by changing a binarization method, wherein the dither pattern (DP)  546  is applied in the image blocks  11  and  13  since they are monotone blocks, and the error diffusion (ED)  547  is applied for the blocks  12 ,  21 ,  22  and  23 . 
     FIG. 8A shows an example of directions to which an error is conveyed. An error of a pixel of interest indicated by “*” is diffused to neighboring pixels in the right (main scanning) direction, the lower (sub scanning) direction, the lower left direction and the lower right direction. In this case, for example, an error in the block  12  where the ED method is applied as shown in FIG. 8B is not conveyed to the block  13  where the DP method is applied, and the error supposedly conveyed to the block  13  is discarded. Instead, the error is conveyed to the lower block  22 , the lower left block  21  and the lower right block  23  via a line error buffer. 
     Note that whether or not a block is a monotone block may be determined by the size of the alternating current component of the frequency component data. 
     &lt;System Structure&gt; 
     FIG. 9 is a conceptualized block diagram showing image processing in the color image system of the present embodiment utilizing an application software. 
     In FIG. 9, a file operation menu (File-Menu)  810  includes a file-open designation menu (FileOpen)  811  and a file print designation menu (filePrint)  812 . When the file-open designation menu  811  is selected, a file-open dialogue (FileOpen)  813  is opened, and the designated file is loaded from a file system  821  by designating a file name listed in the dialogue. Note that when a file is loaded, a window  815  showing an image of the file appears on the display unit. The file operation menu  810  further includes a file-save menu (FileSave), a file environment setting menu (FileEnvSet), a quit menu which instructs quitting of an application and so on. 
     The processing taking place inside the system is indicated by reference numeral  822  to  825 . That is, the designated file “file1.jpg” loaded from the file system  821  is expanded by an expansion module  822  corresponding to an expansion process  520  in FIG. 6, and the expanded image data is temporarily stored in a page memory  823 . In addition, frequency component data  829  of the image data is generated and temporarily stored in a memory (not shown). The image data stored in the page memory  823  is reduced (or enlarged) by a resolution conversion module  824  to match with resolution of a display unit, and the reduced (or enlarged) image data is displayed in the window  815  by a display module  825 . 
     Meanwhile, when the image data is to be printed, the image data is displayed by the operation described above, thereafter a user selects the file-open designation menu  812  to open a file-print dialogue (FilePrint)  814 . Since the dialog  814  indicates a currently-open file name, depressing an OK button will immediately start printing operation of the image data corresponding to the open file. 
     The process taking place inside the system is indicated by reference numeral  822  to  829 . That is, the image data expanded and stored temporarily in the page memory  823  in the above described processing is mapped in a color space (e.g., from a space for R, G and B to a space for Y, M, C, and K) suitable for printing by color conversion and resolution conversion module  824 , which correspond to the color conversion process  532  and the resolution conversion process  541 , then enlarged (or reduced) to match with a print resolution on the basis of the frequency component data  829 , binarized for each color component by a binarization processing module  826  equivalent to the binarization process  545  in FIG. 6, thereafter stored in a band memory  827 . 
     The image data stored in the band memory  827  is sequentially transmitted to an interface unit  831  in a printer unit  830  by an interface unit  828  and stored in a band memory  832  by the interface unit  831 . A printer engine  833  prints a color image print  841  by reading out the image data from the band memory  832  as necessary. 
     As set forth above, according to the present embodiment, when a compressed image is expanded and outputted, resolution conversion and binarization processing is performed based on the frequency component data of an image obtained in the process of expansion operation. Therefore, it is not necessary to perform an additional process (image-matching processing) such as analyzing of frequency component in a local region of an image, making it possible to obtain a high-quality output image in a short period of time. 
     Note that when a color output device for outputting binary information, e.g., a ferroelectric liquid crystal display (FLCD) or the like, is utilized as a display in the color image system of the present embodiment, image data expanded and temporarily stored in the page memory  823  by the above described processing is enlarged (or reduced) by the resolution conversion module  824  to match with a resolution of the display in accordance with the frequency component data  829 , binarized for each color component by the binarization processing module  826  based on the frequency component data  829  and transmitted to the display module  825 , whereby displaying a high quality image in a short period of time as similar to the case of printing operation. 
     [Second Embodiment] 
     Hereinafter, an image processing apparatus of a second embodiment according to the present invention will be described. In the second embodiment, the same reference numerals are assigned to compositions identical to those in the first embodiment and detailed descriptions thereof will be omitted. 
     In the foregoing color image system of the first embodiment, a module for expanding compressed image data, a module for converting resolution and a module for binarization are all independent. Therefore, in order to transfer data between these modules, it is necessary to temporarily generate a data file in a file system or the like. On the other hand, in the color image system according to the second embodiment, these modules are combined to obviate transferring of data between modules, thereby improving the processing speed. 
     &lt;Outline of Processing&gt; 
     FIG. 10 is a block diagram showing overall image processing in the color image system according to the second embodiment. Compressed data  911  indicative of compressed color image data is restored into color image data  913  by an expansion process  912 , and frequency component data  915  is generated. The frequency component data  915  is input to a unit executing an analyzing process  921 , and a binarization process  922  or a binarization process  923  is selectively performed for a specified region (block or the like) in accordance with the analysis result. 
     By virtue of the binarization process adaptively selected in the above manner, the most appropriate processing for each region is performed on the restored color image data  913 . The image data being processed in a unit of a region is combined by combine process  924  and outputted as binarized color image data  925  which corresponds to one page. 
     Herein, the expansion process  912 , analyzing process  921 , binarization processes  922  and  923  and combine process  924  are combined into one module as an output process  929 . 
     &lt;Preview Image&gt; 
     FIG. 11 is a conceptualized diagram showing an example of binarization processing procedure of compressed image data in the image processing apparatus according to the second embodiment. 
     In FIG. 11, a file conversion utility window  1011  includes a file list box  1012 . When a preview button (PreView)  1013  is depressed after selecting a file listed in the list box (in FIG. 11, “file2.jpg” is selected), the image file “file2.jpg” stored in a file system  1021  is sent to a preview image generation module  1041  and a preview image  1051  is displayed on a display unit. Note that the preview image  1051  includes detailed header information of the image file “file2.jpg” to facilitate selection of an image file. 
     A low resolution image or a reduced image would be sufficient enough for the quality of the preview image, however, the image must be displayed quickly. FIG. 12A shows generation of low resolution image data from compressed image data. The process shown as an example in FIG. 12A is where the DC component and a low-frequency component shown in FIG. 12B are extracted ( 1043 ) from compressed image data  1042  having 300 dpi to generate image data having one fourth (75 dpi) of the resolution. Hereinafter, this processing will be briefly explained. 
     Suppose a function denoting original image data is i(x, y) and the corresponding DCT function is I(u, v). A DCT conversion equation is defined as the above described equation (1). The following equation can be obtained by performing an inverse DCT conversion utilizing four coefficients I(0,0), I(0,1), I(1,0), and I(1,1) of the equation (4).                  I        (     x   ,   y     )       =       ∑     u   =   0     1            ∑     v   =   0     1            c        (   u   )            c        (   v   )              I        (     u   ,   v     )       ·   cos            {       (       2      x     +   1     )        u                   π   /   2        N     }     ·   cos          {       2      y     +   1     )        v                   π   /   2        N           }           (   4   )                                
     where 0≦u,v≦1 
     As a result of the above operation, an 8×8 pixel which constitutes the block is reduced to a 2×2 pixel whereby generating an image having one fourth of the original resolution. Note that the resolution of a display apparatus is generally about 75 dpi. Therefore, the low resolution image obtained in the foregoing manner is displayed without further processing. 
     &lt;Conversion Processing&gt; 
     In the file conversion utility window  1011 , when a conversion button (Convert→)  1014  is depressed after selecting a file, a file conversion dialogue (ConvertFile)  1061  is displayed. When an OK button of the dialogue  1061  is operated, the image file “file2.jpg” stored in the file system  1021  is sent to a conversion process module  1031  where processing for expansion, color conversion, resolution conversion, binarization and the like which is appropriate for a target output device are performed. An image file “file2.htn” obtained by processing the image “file2.jpg” is stored in a file system  1022 . By sending the image file “file2.htn” to an output device such as a printer or the like, a desired image is outputted. 
     Since a system printer (SystemPrinter) is selected as a default setting of the target output device, an image size, color conversion, the number of bit to be output and the like are automatically set to match with the system printer. To change the target output device, a “DestinationProfile” box  1062  in the file conversion dialogue  1061  is operated thereby selecting a desired output device. If a profile of the selected output device is registered in the system, an image size, color conversion, the number of bit to be output and the like are automatically set to match with the output device. 
     To change the image size, a “Size” box  1063  in the file conversion dialogue  1061  is operated to select a desired size; alternatively, a size is inputted from a keyboard (not shown) or the like. 
     [Third Embodiment] 
     An image processing apparatus of the third embodiment according to the present invention will now be described. In the third embodiment, the same reference numerals are assigned to compositions identical to those in the first embodiment and detailed descriptions thereof will be omitted. 
     The third embodiment is provided to improve the speed of the process, as similar to the second embodiment. In the apparatus of the third embodiment, each of the processes for expansion of compressed image data, color conversion, resolution conversion and binarization is performed by a single device. In the following description, a printer apparatus comprising processing units for performing the above processes will be described. It is however also possible to supply the processing units as a card mounted on a print circuit board to be embodied in a printer or a personal computer or the like, alternatively a dedicated image processing apparatus may be supplied. 
     &lt;Preview Image&gt; 
     FIG. 13 is a conceptualized block diagram showing a structure of an image processing system according to the third embodiment of the present invention and a process of compressed image data being expanded, binarized and outputted. 
     In FIG. 13, a file selection window  1211  includes a file list box  1212 . When a preview button (PreView)  1213  is depressed after selecting a file listed in the box, the image file e.g., “file2.jpg” stored in a file system  1221  is sent to a preview image generation module  1224  and a preview image  1225  is displayed. Note that the preview image  1225  includes detailed header information of the image file “file2.jpg” to facilitate selection of an image file. 
     &lt;Output Processing&gt; 
     In the file selection window  1211 , when a print button (Print)  1214  is depressed upon selection of a file, image file data e.g., “file2.jpg” stored in the file system  1221  is sequentially transferred to a band memory  1222  and further transferred to a printer unit  1230  via an interface unit  1223 . 
     An interface unit  1231  of the printer unit  1230  sequentially transmits the received data to a conversion process unit  1232 . The conversion process unit  1232  performs processing for expansion, color conversion, resolution conversion, binarization and the like on the inputted data in high speed, and stores the obtained binarized image data in a band memory  1233 . A printer engine  1234  generates a printout  1241  by reading image data out of the band memory  1233 . 
     [Fourth Embodiment] 
     An image processing apparatus of a fourth embodiment according to the present invention will be described below. In the fourth embodiment, the same reference numerals are assigned to compositions identical to those in the first embodiment and detailed descriptions thereof will be omitted. 
     In the fourth embodiment, not only the resolution conversion method and the binarization method, but also a color conversion method is changed in accordance with the image frequency component  533 , as shown in FIG.  14 . Moreover, in the binarization process, a plurality of different dither patterns are selectively utilized in accordance with the image frequency component  533 , instead of changing between the dither pattern method and the error diffusion method. 
     &lt;Changing of Color Conversion Method&gt; 
     Changing of a color conversion method in the color conversion process  532  is now described. 
     In the color conversion process  532 , four frequency components I(0,0), I(0,1), I(1,0) and I(1,1) are referred to, and a color conversion method (color matching method) is changed in accordance with a state of the pattern of the frequency components. For instance, in case of a monotone block, an image in the block is highly likely to be a computer graphic image (CG image). In consideration of the fact that the CG image is generated on a color monitor, a color conversion parameter-appropriate for a color monitor is utilized. When a user knows the characteristics of the color monitor used, a color conversion parameter which matches the characteristics is utilized, as a matter of course. 
     If density variance of pixels in the block is high (high-frequency components are included), the image is highly likely to be a natural image; therefore, a color conversion parameter appropriate for a natural image is utilized. 
     Although the changing of the color conversion parameter may be performed for each block, a region in which plural units of M×N (e.g., 4×4 block) blocks are combined may be newly defined to change the parameter. 
     Further, depending upon whether the image is a CG image or a natural image, the color space compression pursuing colorfulness or the color space compression pursuing perception may be selectively performed at the time of color space compressing operation. 
     &lt;Changing of Binarization Method&gt; 
     Next, changing of a binarization method in the binarization process  545  will be described. 
     As shown in FIG. 15A, four frequency components I(0,0), I(0,1), I(1,0) and I(1,1) are referred to in the binarization process  545 , whereupon an appropriate dither pattern is selected from dither patterns 1 to 4 in accordance with the state of the pattern of the frequency components to perform binarization. Note that the dither patterns are not limited to those four patterns shown in FIG. 15A, but an arbitrary number of arbitrary dither patterns can be utilized. 
     FIG. 15B is a diagram showing generation of the most appropriate image in each block by a dither pattern being selected and combined. 
     In FIG. 15B, since the blocks  11 ,  13  and  23  are monotone blocks, the dither pattern 1 is selected. Although the block  22  is not a monotone block, density variance is minor; thus the dither pattern 1 is selected. 
     Meanwhile, in the block  12 , a dither pattern is rearranged by combining a non-rectangular dither pattern  3  and a rectangular dither pattern 2, whereby generating a binarized image in the block  12 . In the block  21 , a dither pattern is rearranged by combining two dither patterns  2  and  4  whose sizes are different, whereby generating a binarized image in the block  21 . 
     &lt;Summary&gt; 
     As set forth above, in order to generate high quality image, an additional step (image-matching processing), such as analyzing of frequency component in a partial region of a processing image, is necessary. Although such step raises a problem of extremely long processing time, by virtue of the foregoing embodiments, quality of an output image can be improved and the processing time can be reduced at the time of expanding and outputting compressed image data. 
     According to each of the above described embodiments, the time necessary for the image-matching processing can be reduced by utilizing frequency component data obtained by the above described DCT conversion, thereby attaining a high quality image and achieving reduction of processing time. 
     FIG. 16 shows how the time required for image-matching processing is reduced. The chart shows the time required for executing each process. 
     As shown in FIG. 16, conventionally the series of processing have been sequentially performed in the order of expansion, resolution conversion, image-matching, and binarization. However in the present invention, processing for expansion, resolution conversion, and binarization is performed, omitting the image-matching process. Therefore, the time necessary for the image-matching process can be excluded, reducing the entire processing time. 
     Further, when each process of expansion, resolution conversion and binarization is independently executed, opening/closing operation of an image data file, input/output operation of the data and the like is necessary for each process. Therefore, the number of times the file system being accessed is increased, resulting in reducing the processing speed of the entire process. In the foregoing second and third embodiments, these processes are combined together so that opening/closing operation of the image data file is performed only once, and that input/output operation of the data is necessary only for the amount of data corresponding to one image. Accordingly, fast processing can be realized. 
     [Other Embodiments] 
     Note that the present invention can be applied to a system constituted by a plurality of devices (e.g., a host computer, an interface unit, a reader, a printer or the like) or to an apparatus comprising a single device (e.g., a copy machine, facsimile apparatus, or the like). 
     Furthermore, the object of the present invention can be attained by supplying a storing medium (e.g., disk  14  in FIG. 1) storing program codes of a software which realizes the function of the present embodiment, to a system or an apparatus (e.g., computer  1  in FIG.  1 ), and by the system or a computer (or CPU or MPU) of the apparatus reading and executing the program codes stored in the storing medium. In this case, the program codes read from the storing medium realize the above described functions of the present embodiments and the storing medium storing the program codes constitutes the present invention. As a storing medium for supplying program codes, for example, a floppy disk, hard disk, optical disk, magneto optical disk, CD-ROM, CD-R, a magnetic tape, a non-volatile memory card, a ROM and the like can be utilized. 
     Furthermore, by the computer executing the read-out program codes, not only the above described functions of the present embodiments are realized, but also an OS or the like operated on the computer executes a part of or the entire processing based on instructions of the program codes, thereby realizing the functions according to the present embodiments. 
     Moreover, after the program codes read from the storing medium is written in a function extension card inserted into a computer, or in a memory embodied in a function extension unit connected to the computer, a CPU included in the function extension card or the function extension unit performs a part of or the entire processing, thereby realizing the functions according to the present embodiments. 
     When the present invention is applied to the above described storing medium, a program code corresponding to the foregoing flowchart is stored in the storing medium. More particularly, each module shown in the memory map in FIG. 17 is stored in the storing medium. In other words, at least the program codes for each of the “expansion” module, “resolution conversion” module and “binarization” module needs to be stored in the storing medium. Note that each of the “expansion,” “color conversion,” “resolution conversion” and “binarization” modules may be combined to a “conversion processing module.” 
     Further, in application of the present invention, an image block is not limited to a rectangle, but may be a substantially hexagon, or each block may have an irregular size and a shape, and may overlap with neighboring blocks. A method of resolution conversion or binarization is not limited, as long as the method enables to generate a high-quality image by appropriately changing a method in accordance with a frequency component of an image. 
     Furthermore, the expansion means for expanding coded image data does not necessarily have to include a reproduction function of an original image, but may be configured such that necessary information is obtained from the coded data to perform the least-required processing. For instance, the image data may be decoded into an intermediate code without being reproduced. Therefore, the expansion means according to the present invention is not the type of processing means distinguished by whether or not an original image is partially or temporarily generated in the entire process (the expansion means according to the present invention does not necessarily produce an original image partially or temporarily, by its processing). In other words, even if an original image is not reproduced, as long as frequency data of an image is utilized in its processing, the concept of the present invention is adopted. For instance, instead of generating an image file by binarizing an image obtained by expanding a compressed file including a compressed original image, a case where a binarized image file is directly generated from a compressed file, is also considered as adoption of the concept according to the present invention. 
     Moreover, in each of the foregoing embodiment, the descriptions are given for an example where color image data is outputted to a color output device for outputting binary information (e.g. ink-jet color printer or ferroelectric liquid crystal display (FLCD)), therefore output data needs to be binarized. However in the present invention, it is not limited to binarization, but a color-depth of data can be changed to an arbitrary value. For instance, the present invention can be applied to a case where full-color coded image data is expanded, converted to index color data where each of the R, G, and B colors has 8 bit or 4 bit (i.e. octal representation or quaternary representation), based upon obtained image frequency component data, thereafter re-encoded as necessary and stored in a storing medium or transmitted via a transmission path. 
     The concepts exemplified in each of the above embodiments can be arbitrarily combined to realize an apparatus. 
     Accordingly, as set forth above, the present invention provides an image processing apparatus and method thereof which can obtain high-quality image data in short period of time. 
     The present invention is not limited to the above embodiments and various changes and modifications can be made within the spirit and scope of the present invention. Therefore, to appraise the public of the scope of the present invention, the following claims are made.