Abstract:
In an image forming apparatus, a control section performs a control to compress/decompress at least one of first image data and second image data by one of a first compression/decompression method and a second compression/decompression method on the basis of the determination of the kind of an original, and to perform one of a first printing operation and a second printing operation.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an image forming apparatus and method, and more particularly to an image forming apparatus and method for performing printing by subjecting image data of an original obtained by a scanner, etc. to image processing. 
   2. Description of the Related Art 
   In these years, some types of color digital copying machines have automatic color select functions (ACS). 
   Jpn. Pat. Appln. KOKAI Publication No. 2002-165101, for instance, discloses an image forming apparatus having a color determination section that determines whether an original scanned by a color CCD sensor is a black-and-white one or a color one, and a setting section that sets a black-and-white/color mode for image formation on the basis of the determination. In the prior-art techniques including this one, the black-and-white/color determination can be made by the ACS. However, it is not possible to subject a black-and-white character original and a black-and-white photo original to different processes. As regards a photo original, a gray-scale process is important for the image quality. However, a gray-scale process is not important for the image quality in the case of a character original. Accordingly, if a character original is subjected to a process that places priority on speed, and not on gray-scale processing, productivity will be enhanced. 
   BRIEF SUMMARY OF THE INVENTION 
   There is a need for an image forming apparatus and method that can achieve suppression in degradation of image quality and enhancement of productivity at the same time, by performing automatic determination of the kind of an original and processing image data through an image processing section provided in accordance with the determined kind of original. 
   According to an aspect of the present invention, there is provided an image forming apparatus comprising: a first processing section that subjects image data to a first process, and outputs first image data that has been subjected to the first process; a second processing section that subjects image data to a second process, and outputs second image data that has been subjected to the second process; a compression/decompression section that compresses/decompresses at least one of the first image data and the second image data by one of a first compression/decompression method and a second compression/decompression method; a printer section that performs one of a first printing operation and a second printing operation; a determination section that determines a kind of an original; and a control section. The control section performs a control to compress/decompress at least one of the first image data and the second image data by one of the first compression/decompression method and the second compression/decompression method on the basis of the determination by the determination section, and to perform one of the first printing operation and the second printing operation. 
   Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention. 
       FIG. 1  is a control block diagram of a control panel section according to an embodiment of the invention; 
       FIG. 2  is a control block diagram of a scanner section according to the embodiment; 
       FIG. 3  is a control block diagram of a printer section according to the embodiment; 
       FIG. 4  is a control block diagram of a basic processing unit according to the embodiment; 
       FIG. 5  schematically shows the structure of an image processing section according to the embodiment; 
       FIG. 6  shows a compression/decompression section and a page memory according to the embodiment; 
       FIG. 7  is a histogram showing a density and a frequency relating to a color original in the embodiment; 
       FIG. 8  is a histogram showing a density and a frequency relating to a monochromatic character original in the embodiment; 
       FIG. 9  is a histogram showing a density and a frequency relating to a monochromatic photo original in the embodiment; and 
       FIG. 10  is a flow chart illustrating a process of a copying operation in the embodiment. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   An embodiment of the present invention will now be described with reference to the accompanying drawings. In the embodiment, this invention is applied to a color digital copying machine. 
     FIGS. 1 to 4  show control blocks of the color digital copying machine. The color digital copying machine has a main CPU  40  (control unit), a control panel CPU  10 , a scanner CPU  20  and a printer CPU  30 . These CPUs control a basic processing unit  4 , a control panel section  1 , a scanner section  2  and a printer section  3 , respectively. The main CPU  40  communicates with the control panel CPU  10 , scanner CPU  20  and printer CPU  30  and controls the same. 
   The control panel CPU  10  is connected to a ROM  11  and a RAM  12 . Based on data stored in the ROM  11  and RAM  12 , the control panel CPU  10 , for example, detects operations of switches on the control panel  13 , turns on/off LEDs on the control panel  13 , and controls a display on the control panel  13 . 
   Based on data stored in a ROM  21  and RAM  22 , the scanner CPU  20  controls a mechanism section  23  including a motor, a solenoid, etc. (not shown), and also controls an automatic document feeder (ADF)  24 , a coordinate input device (editor)  25 , an analog/digital converter circuit (A/D)  26 , a shading correction circuit (SHD)  27  and a line memory  28 . A CCD section  29  is connected to the A/D converter  26 . The CCD section  29  scans an image by means of a monochromatic CCD sensor and a color CCD sensor. As is shown in  FIG. 4 , an image scanned by the monochromatic CCD sensor is processed by a monochromatic CCD scan processing section  291 , and an image scanned by the color CCD sensor is processed by a color CCD scan processing section  292 . The monochromatic CCD sensor that scans an original to produce a corresponding monochromatic image has a higher scan speed and a higher resolution than the color CCD sensor that scans an original to produce a corresponding color image. 
   On the basis of data stored in a ROM  31  and a RAM  32 , the printer CPU  30  controls a mechanism section  33  including a motor, a solenoid, etc. (not shown), and also controls a sorter  34 , a large cassette feeder (LCF)  35 , a laser conversion circuit  36 , and a laser drive circuit  38  that controls a semiconductor laser  37 . 
   The main CPU  40  controls the entirety of the color digital copying machine according to control programs stored in a ROM  41  and a RAM  42 . The ROM  41  stores various parameters to be used at the time of image processing. 
   A data switch/buffer memory section  43  effects switching as to where data scanned by the scanner section  2  is to be sent, and which data is to be sent to the printer section  3 . In addition, the data switch/buffer memory section  43  performs buffering. Details of the structure and operation of an imaging processing section  44  will be described later. The imaging processing section  44  is provided with, for example, circuits for generating histograms from image data and correcting the image data based on the histograms. A compression/decompression section  45  compresses/decompresses image data. A page memory  46  stores image data in units of a page. A display memory  47  stores image data to be displayed on a display  48 . A printer controller  49  develops code data from a personal computer  50  into image data. A display font ROM  51  develops code data onto the display memory  47 . A print font ROM  52  develops code data onto the page memory  46 . A compression memory  53  stores data compressed by the compression/decompression section  45 . 
   The main CPU  40  is also connected via an I/F controller  54  to a hard disk drive (HDD)  55 , an optical disk drive  56  and a facsimile processing section  57 . The HDD  55  stores various programs, such as OCR automatic recognition software, for performing character recognition on the basis of the data stored in the page memory. The facsimile processing section  57  forwards processed image data to an external communication line (not shown) connected to the present copying machine, or receives image data from the external communication line. 
   In the color digital copying machine with the above structure, image data scanned by the scanner section  2  is subjected to image processing in the image processing section  44 . Based on the processed image data, the printer section  3  performs image formation. 
   The image processing section  44  will now be described with reference to the control block diagram of  FIG. 5 . In  FIG. 5 , double-line arrows indicate flows of image data scanned by the scanner section  2 , which is to be output to the printer section  3  via the image processing section  44 . 
   Image data scanned by the monochromatic CCD sensor and subjected to correction processing in the monochromatic CCD scan processing section  291 , or image data scanned by the color CCD sensor and subjected to correction processing in the color CCD scan processing section  292 , is input to a first selection section  441 . At the time of scan, the image data selected by the first selection section  441  is delivered to either a first scan data processing section  442  or a second scan data processing section  443 . At the time of pre-scan, the image data selected by the first selection section  441  is delivered to a histogram calculation section  444 . How the first selection section  441  selects output image data at the time of scan will be described later. 
   The first scan data processing section  442  (first processing section) subjects the monochromatic image data input from the monochromatic CCD scan processing section  291  to filtering processing, to density adjustment processing, and to gray-scale processing using an error diffusion process that is a pseudo-half tone process. In other words, the first scan data processing section  442  performs processes that place priority on a processing speed (V 1 ). For this purpose, the processing section  442  decreases the amount of image data to a lower bit (M bit) than in the second scan data processing section  443  in front of the compression/decompression section  45 . These processes achieve handling for shortening an access time to the page memory  46  to realize electronic sorting, and achieve effective use of OCR automatic recognition software. 
   The second scan data processing section  443  (second processing section) subjects RGB color image data input from the color CCD scan processing section  292  to color conversion processing, filtering processing and density adjustment processing. The processing section  443  also subjects monochromatic image data input from the monochromatic CCD scan processing section  291  to color conversion processing, filtering processing and density adjustment processing. In other words, the second scan data processing section  443  performs processes that place priority on image quality, and not on a processing speed (V2, V1&gt;V 2 ). Specifically, the processing section  443  prioritizes gray-scale reproducibility as in the case of color images and monochromatic photo images, and makes the amount of image data greater than in the first scan data processing section  442  (N bit, N&gt;M) in front of the compression/decompression section  45 . 
   Various parameters used for the color conversion, filtering and density adjustment in the second scan data processing section  443  are stored in the ROM  41  in association with monochromatic image data and color image data, respectively. Such parameters are selected, as needed, by the main CPU  40  on the basis of, e.g. the kind of each page of original documents. As regards the processing sections other than the processing section  443 , various parameters are similarly stored in the ROM  41  and selected by the main CPU  40 , as needed. 
   Image data processed by the first scan data processing section  442  and second scan data processing section  443  is output to a second selection section  445 . How the second selection section  445  selects output image data will be described later. Image data from the second selection section  445  is output to the compression/decompression section  45 . 
   As is shown in  FIG. 6 , when monochromatic-character image data has been input to the compression/decompression section  45 , a variable-length compression/decompression processing section  451  is selected to process the image data. When color image data and monochromatic-photo image data has been input to the compression/decompression processing section  45 , a fixed-length compression/decompression processing section  452  for color data and the variable-length compression/decompression processing section  451  are both selected to process the image data. For example, color image data is compressed by the fixed-length compression/decompression processing section  452  and then further compressed by the variable-length compression/decompression processing section  451 . The selection of each processing section  451 ,  452  is made by the control of the main CPU  40  in accordance with the kind of each page of originals. 
   Data compressed by the compression/decompression section  45  is temporarily stored in the page memory  46 . Then, the data is decompressed by the compression/decompression section  45 . The decompressed data is input to a first print data processing section  446  and a second print data processing section  447 . 
   The first print data processing section  446  (third processing section) performs a gray-scale process that places priority on a processing speed and is suitable for low-bit (M-bit) image data from the first scan data processing section  442 . The first print data processing section  446  subjects the input image data to a smoothing process and a monochromatic multi-value process and outputs the resultant image data to the printer section  3 . 
   The second print data processing section  447  (fourth processing section) performs a gray-scale process that places priority on an image quality and is suitable for greater-number bit (N-bit, N&gt;M) data than in the first print data processing section  446 . The second print data processing section  447  subjects the input image data to a black-adding process and a gray-scale process and to a color multi-value process and outputs the resultant image data to the printer section  3 . 
   Various parameters used for the black-adding process and gray-scale process performed in the second print data processing section  447  are stored in the ROM  41 . The various parameters are selected by the control of the main CPU  40 . In the case of image data of a monochromatic photo original, the main CPU  40  sets parameters for monochromatic processing. In the case of image data of a color original, the main CPU  40  sets parameters for color processing. 
   The image data processed by the first print data processing section  446  and second print data processing section  447  is output to a third selection section  448 . How the third selection section  448  selects output image data will be described later. The image data from the third selection section  448  is output to the printer section  3 . 
   The printer section  3  performs a color printing operation in the case of color image data and monochromatic photo image data, and performs a monochromatic printing operation in the case of monochromatic character image data. This selection is effected by a communication control from the main CPU  40  to the printer CPU  30  in accordance with the kind of each page of originals. 
   The histogram calculation section  444  calculates histogram information of an original on the basis of image data pre-scanned by the color CCD scan processing section  292 . For example, input image data (0 to 255) is divided by a predetermined number, e.g. 8, and the frequency of RGB data in each divided data area is calculated. The frequency in each divided data area is read by the main CPU  40  to determine the kind of original. The determination of the kind of original is determined on the basis of the frequency variance of RGB data and the frequency ratio among the respective divided data areas. For example, the determination is effected as follows. 
     FIG. 7  illustrates a determination result of a color original, which is obtained by the main CPU  40 . In  FIG. 7 , the variance in frequency of RGB data in each divided data area is greater than a predetermined threshold A.  FIG. 8  illustrates a determination result of a monochromatic character original, which is obtained by the main CPU  40 . In  FIG. 8 , the variance in frequency of RGB data in each divided data area is not greater than the threshold A. In addition, the frequency in a high-density side divided data area (8th divided data area) is greater than a threshold B and the frequency in the other divided data areas is not greater than the threshold.  FIG. 9  illustrates a determination result of a monochromatic photo original, which is obtained by the main CPU  40 . In  FIG. 9 , the variance in frequency of RGB data in each divided data area is not greater than threshold A, and there are a plurality of divided data areas, which have a frequency greater than a threshold C. 
   Based on the determination result of each page of originals, which is obtained by the histogram calculation section  444 , the main CPU  40  controls the first selection section  441 , second selection section  445  and third selection section  448  and makes selection of output image data from each selection section. In addition, based on the determination result of each page, the main CPU  40  selects parameters to be set in the second scan data processing section  443 , compression/decompression section  45  and second print data processing section. 
   When the main CPU  40  has determined a color original, it sets a first image-quality preference mode as an image data processing mode, which places priority on color reproduction. In the first image-quality preference mode, the selection sections  441 ,  445  and  448  are operated to make effective the output results from the color CCD scan processing section  292 , second scan data processing section  443  and second print data processing section  447 . In this case, the main CPU  40  controls the printer CPU  30  to effect full-color printing in a color operation mode. 
   When the main CPU  40  has determined a monochromatic photo original, it sets a second image-quality preference mode as an image data processing mode, which places priority on monochromatic-photo reproduction. In the second image-quality preference mode, the selection sections  441 ,  445  and  448  are operated to make effective the output results from the monochromatic CCD scan processing section  291 , second scan data processing section  443  and second print data processing section  447 . In this case, the main CPU  40  controls the printer CPU  30  to effect monochromatic printing in a color operation mode. 
   In the second image-quality preference mode, the output from the monochromatic CCD sensor is used. Thus, the scan of the original may be performed in accordance with the scan speed of the monochromatic CCD sensor. Thereby, the scan time can be made shorter than in the first image-quality preference mode using the output of the color CCD sensor. In addition, in this case, since the image data obtained from the monochromatic CCD scan section  291  is used, it is possible to prevent disadvantages in resolution, such as thinning in characters and lines, which may occur when using the image data obtained by the color CCD scan processing section  292 . 
   When the main CPU  40  has determined a monochromatic character original, it sets a speed preference mode as an image data processing mode, which places priority on a processing speed with the amount of data reduced. In the speed preference mode, the selection sections  441 ,  445  and  448  are operated to make effective the output results from the monochromatic CCD scan processing section  291 , first scan data processing section  442  and first print data processing section  446 . In this case, the main CPU  40  controls the printer CPU  30  to effect monochromatic printing in a monochromatic operation mode. 
   In this case, like the second image-quality preference mode, the output from the monochromatic CCD sensor is used. Thus, a high-speed scan operation can be achieved. 
   Referring to a flow chart of  FIG. 9 , a description will now be given of an example of control at the time the color digital copying machine produces a copy in an automatic original determination mode. 
   To start with, in step ST 101 , the main CPU  40  sets the first selection section  441  such that an output destination of image data is selected to be the histogram calculation section  444 . In step ST 102 , the main CPU  40  performs prescan. Specifically, an image of an original is scanned by the color CCD sensor, and the scanned image data is processed by the color CCD scan processing section  292 . The resultant data is output to the histogram calculation section  444 . 
   In step ST 103 , the histogram calculation section  444  calculates the frequency of RGB pixels of the input image data in a predetermined number of divided image data areas. The predetermined number is 8, for instance. 
   In step ST 104 , the main CPU determines the kind of original on the basis of the result from the histogram calculation section  444 . As mentioned above, the determination is made based on the frequency variance of RGB data and the frequency ratio among the divided areas. If a color original is determined, the process advances to step ST 105 . If a monochromatic photo original is determined, the process advances to step ST 107 . If a monochromatic character original is determined, the process advances to step ST 109 . 
   In step ST 105 , the above-described first image-quality preference mode is set as an image processing mode. Based on this setting, output image data from the respective selection sections and parameters are selected, and image processing is carried out. In step ST 106 , the main CPU  40  controls the printer CPU  30  based on the processed image data, and the printer section  3  is operated to effect full-color printing in a color operation mode. 
   In step ST 107 , the above-described second image-quality preference mode is set as an image processing mode. Based on this setting, output image data from the respective selection sections and parameters are selected, and image processing is carried out. In step ST 108 , the main CPU  40  controls the printer CPU  30  based on the processed image data, and the printer section  3  is operated to effect monochromatic printing in the color operation mode. Then, the process is completed. 
   In step ST 109 , the above-described speed preference mode is set as an image processing mode. Based on this setting, the respective selection sections are operated, and image processing is carried out. In step ST 110 , the main CPU  40  controls the printer CPU  30  based on the processed image data, and the printer section  3  is operated to effect monochromatic printing in a monochromatic operation mode. Then, the process is completed. 
   In this example of control, one copy has been produced. When originals are to be successively scanned and copied by means of the ADF  24 , the above-described operation may be repeated in accordance with the number of originals. 
   A description will now be given of the operation of the color digital copying machine at the time a monochromatic photo original is to be copied in the automatic original determination mode. 
   The user places a monochromatic photo original on an original table (not shown). The user then operates the control panel  13  to start a prescan operation in the automatic original determination mode. 
   The monochromatic photo original is determined by a calculation result of the histogram calculation section  444  based on the image data scanned by the prescan operation. The calculation result is that the variance in frequency of RGB data in each of divided data areas divided by a predetermined number (e.g. 8) is not greater than the threshold A and there are divided data areas, which have a frequency greater than threshold C. 
   Since the monochromatic photo original has been determined, the second image-quality preference mode is set. Specifically, the first selection section  441  selects the output result from the monochromatic CCD scan processing section  291 , the second selection section  445  selects the output result of the second scan data processing section  443 , and the third selection section  448  selects the output result of the second print data processing section  447 . At this time, the main CPU  40  selects parameters corresponding to monochromatic image data. 
   Specifically, such setting is effected that the image data from the monochromatic CCD scan processing section  291  is subjected to a color conversion process for monochromatic data in the second scan data processing section  443 , and the data, which has been subjected to filtering and density adjustment, is compressed and decompressed in both the variable-length compression/decompression processing section  451  and fixed-length compression/decompression processing section  452  of the compression/decompression section  45 . The processed data is then stored in the page memory  46 . 
   The image data from the page memory  46 , which has been decompressed by the compression/decompression section  45 , is subjected to monochromatic multi-value processing such as black-adding processing and grayscale processing in the second print data processing section  447  in which parameters for monochromatic processing have been set. The processed data is then output to the printer section  3 . 
   The printer section  3  performs monochromatic printing in the color operation mode on the basis of the input image data. Thereby, a copy of the monochromatic photo original is produced. Accordingly, the color digital copying machine can realize copying of a monochromatic image with high image quality, without sacrificing the resolution for thin characters, thin lines, etc. 
   The color digital copying machine of this embodiment performs the prescan in order to determine the kind of each page of originals to be one of a color original, a monochromatic photo original and a monochromatic character original. Based on the determination result, the copying machine sets one of the first image-quality preference mode, second image-quality preference mode and speed preference mode. In addition, in accordance with the kind of original, the copying machine selects the processing sections provided in the image processing section  44 , thereby carrying out an image data process and a compression/decompression process, and reducing the amount of data in the page memory  46 . Therefore, this copying machine can enhance productivity while suppressing degradation in image quality. 
   For example, where the image processing section is constructed such that the second scan data processing section  443  performs the image processing using both image data from the monochromatic CCD scan processing section  291  and color CCD scan processing section  292 , the following structure may be adopted. That is, when the original has been determined to be a color one or monochromatic photo one, the first selection section  441  may output both image data from the monochromatic CCD scan processing section  291  and color CCD scan processing section  292  to the second scan data processing section  443 . In short, unlike the embodiment, the image data to be output from the first selection section  441  and second selection section  445  may not be selected to be one image data. 
   Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.