Abstract:
An image process comprising inputting image data, performing block selection of objects in the input image data, discriminating whether each block of the input image data is character or non-character image data, detecting a feature of each block of the character data without utilizing edge portions of the character data, performing an image process on each block of the character data based on the detected feature of the character data, and performing an image process on the non-character image data, and outputting the processed image data. The detected feature of the character data may be a foreground or background color of the character data. The block selection detects edge portions of the character data and utilizes portions of the character data internal to the edge portions in detecting the feature of the character data. The foreground color detection process may comprise converting input color component values of the character data to color space values, determining an average color space value from the converted color space values, comparing the average color space value to a threshold value, and determining whether or not the character data is black based on the comparison result. Additionally, the input step may comprise selecting a processing mode of the image data based on a type of image being input, wherein each block of the input image data is discriminated based on the selected processing mode. The processing mode may include one of a text mode, a photo/illustration mode, a magazine mode and a mixed document mode.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to image processing in digital color copiers. More specifically, the present invention relates to image processing to discriminate whether input image data is character data or non-character image data by performing block selection and performing an image process on the character data. 
   2. Description of the Related Art 
   Copy machines contain an image processing unit that includes a scanner which scans an input image. When the input image is scanned, the conventional processing unit detects, on a pixel-by-pixel basis, whether input data is text or a continuous tone image by detecting edges of text objects as well as the color of the text objects. The image processing unit then applies an appropriate image process to the contents of the input image based on the type of image data detected. For example, if black text is detected, the edge detection process may result in application of an edge enhancement process that applies only black toner in order to sharpen the output image by making the edge clearer. If a continuous tone image area is detected, a smoothing process may be applied to smooth the rich colored output image. 
   However, such conventional image processes have drawbacks in that, since the color and edge detection processes are performed on a pixel-by-pixel basis, it is not easy to detect the color of text objects. For instance, the edge portion of a text object is generally neither black nor white in detail, but rather, generally appears to have some chroma, i.e. it looks like a colored pixel. Thus, some black text objects may be misjudged as being non-black. In order to address this misjudgment, conventional systems apply a threshold test for determining whether or not an object is black. The threshold value can be adjusted to reduce the misjudgment, depending on the precision of the scanner. However, one drawback with this technique is that low saturation colored text is often detected as black text. 
   Another drawback of performing the processing on a pixel-by-pixel basis is that the image processing unit generally assumes that dark colors are foreground colors and light colors are background. However, where the text is actually white with a dark background color, conventional copiers have trouble performing text detection. 
   Additionally, in performing the image processing, conventional copiers provide pre-set functions for a user to select the type of original document being scanned so as to set a type of image recognition process to be used in scanning the input image. That is, based on the pre-set function selected, the image recognition process will be pre-set to detect text only, continuous tone images, or a combination of both, thereby reducing misjudgment of text and non-text data during the detection process. However, the conventional functions generally result in enabling or disabling text detection, preparing appropriate parameters for text detection, preparing appropriate parameters of an image filter and RGB to CMYK conversion, and selecting printout resolution which are not conducive for performing image processing by block selection. 
   SUMMARY OF THE INVENTION 
   The present invention addresses the foregoing by utilizing an image processing technique that processes input image data by performing block selection rather than performing a process on a pixel-by-pixel basis. According to the invention, the objects of the input image are detected by block selection and are discriminated as being text or not-text. Then, for each text object, the foreground color is determined using the non-edge foreground text data. After collecting the foreground data, the average foreground color is calculated in a color space such as Lab color space. Utilizing the average color information, a determination is made whether the text object is black or not. 
   As a result of the foregoing, the misjudgment of color text as black text, and vice versa, is reduced. Moreover, since the foreground and background colors are detected, a different image process can be applied depending upon which background and foreground colors are detected. 
   Thus, according to one aspect, the invention processes image data by inputting image data, performing block selection of objects in the input image data, discriminating whether each block of the input image data is character or non-character image data, detecting a feature of each block of the character data without utilizing edge portions of the character data, performing an image process on each block of the character data based on the detected feature of the character data, and performing an image process on the non-character image data, and outputting the processed image data. The block selection may be performed by an algorithm that detects edge portions of the character data and utilizes portions of the character data internal to the edge portions in detecting the feature of the character data. The detected feature of the character data may be a foreground color of the character data or a background color of the character data. The foreground color detection process may be performed by converting input color component values of the character data to color space values, determining an average color space value from the converted color space values, comparing the average color space value to a threshold value, and determining whether or not the character data is black based on a result of the comparison. 
   As a result of the foregoing, the misjudgment of low saturation color text as black, and the misjudgment of black text as color text is reduced since the unreliable edge portions of the character data are not considered in the color detection process. That is, where the edge portions may normally exhibit some chroma due to printing with process black ink, the process of the present invention removes the edge portions having chroma from the color detection process and instead, utilizes the more reliable internal portions. Additionally, since the foreground and background colors are detected, a different image process can be applied depending upon the detected background and foreground colors. 
   In another aspect, the process of inputting the image data may comprise selecting a processing mode of the image data based on a type of image being input. Each block of the input image data is discriminated based on the processing mode selected. The processing mode selected may be one of a text mode, a photo/illustration mode, a magazine mode and a mixed document mode. The foregoing modes assist in the block selection processing of image data and can accelerate the processing of the image data by pre-setting the processes to be performed on the image data. 
   In a further aspect, the invention may apply a more intelligent rule by performing block detection on a word-by-word basis. Thus, the character data may comprise each of a plurality of characters of a word and the detected feature of each character in the word may be compared with one another. This process provides for correcting the detected color of some of the letters based on the detected color of other letters. For instance, if some letters in a word are detected as being black text while other letters are detected as being low saturation color text, an image process to correct the low saturation color text to be black text may be applied. 
   This brief summary has been provided so that the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the following detailed description of the preferred embodiment thereof in connection with the attached drawings. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a sectional view of a color copier according to an embodiment of the present invention. 
       FIG. 2  is a block diagram showing an image processing unit according to the present invention. 
       FIG. 3  depicts a display panel for setting image processing options according to the invention. 
       FIGS. 4A  to  4 D depict examples of various types of documents. 
       FIG. 5  depicts process steps of an image process according to the invention. 
       FIG. 6  depicts process steps of a text color detection process according to the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  shows a sectional view of an image processing apparatus according to one embodiment of the present invention. In the apparatus of FIG.  1 , image scanner  201  reads an original document, and digitally processes read pixel data of the original document into digital signals. Printer  200  then prints out an image corresponding to the original document read by image scanner  201  on a printing sheet in full color. 
   In image scanner  201 , original document  204  is set on a platen glass, covered with a document cover  202 , and exposed by halogen lamp  205 . Reflected light from original document  204  is further reflected by mirrors  206  and  207 , then focuses on CCD  210  for identifying R, G, and B signals after passing through the lens  208 . It should be noted that lens  208  is covered by infrared filter  231 . 
   In the preferred embodiment, each row of sensors in CCD  210  for reading respective color components is composed of 5000 pixels, thus CCD  210  an read across the shorter side of an A3-sized original, namely 297 mm, at 400 dpi resolution. CCD  210  separates color information of original document  204  into full-color information of R, G and B components, and converts the full-color information into color signals. 
   In addition, standard white board  211  generates correction data for correcting read data by R, G, B photo sensors  210 - 1  to  210 - 3  of CCD  210 . Standard white board  211  has uniform reflection characteristics in the visible light range, and appears white. After correcting the data, CCD  210  then sends the signals to signal processing unit  209 . 
   It should be noted that, halogen lamp  205  and mirror  206  move at speed v, and mirror  207  moves at speed (½)v in a perpendicular direction with respect to an electrical scanning direction of CCD  210  (a main scanning direction). The entire area of original document  204  is scanned in this manner. 
   Further, in signal processing unit  209 , the read signals are electrically processed and separated into color components of magenta (M), cyan (C), yellow (Y), and black (Bk), then sent to printer  200 . for each scanning operation by image scanner  201 , one of the color component data of M, C, Y, and Bk is sent to printer  200 . Thus, by scanning original document  204  four times, one color image is formed. 
   Image scanner  201  also includes control panel  228 . Control panel  228  includes various buttons as well as a display panel that provides a user with the ability to select and set various image processing options. The display panel may be a touch panel display from which the user can select processing options by touching a desired option on the display. An example of such a touch panel display depicting various processing options is shown in FIG.  3 . 
   As seen in  FIG. 3 , touch panel display  300  may include an option to reduce  301 , enlarge  302 , or to fit the image on the output paper size (fit image  303 ). Additionally, using zoom  304 , a user can set the output image to a specified percentage of the original document. Options to select an original document size  305  (e.g. A3, A4, Letter, Legal, etc.), select an output document size  306 , and to select a color image  307  or a greyscale image  308  may also be included in display  300 . Further, finishing options  310  such as collating and stapling, and two sided copying  311  may be included. 
   In the present invention, additional processing options may include selecting the type of image contained in the input document (i.e. text mode  315 , mixed image mode  316 , photo mode  317  or magazine mode  318 ). In  FIG. 3 , processing modes  315  to  318  provide a way for the user to preset an image process in image scanner  201 . That is, depending on the type of data contained on the original document, the user can select an image processing mode that assists in the block selection processing of the document. For instance, if the document contains only text such as document  325  shown in  FIG. 4A , the user can select text mode  315  so that image scanner  201  is preset to perform block selection of text only. In the absence of selecting text mode  315 , image scanner  201  normally performs a block selection recognition process to detect the type of data contained in the document and then processes text blocks and image blocks accordingly. However, the recognition portion of the block selection process increases the processing time. Therefore, selecting a text only option expedites the recognition portion of the block selection process by informing image scanner  201  that the original document only contains text. As a result, the image scanner performs the block selection knowing that the original document only contains text and therefore the image scanner does not have to perform processes that are required for images. 
   As stated above, in addition to text mode  315 , the present invention also provides for mixed document mode  316 . An example of a mixed document is shown in FIG.  4 B. As seen in  FIG. 4B , mixed document  326  contains text data  327  and  329 , and image data  328 . When mixed mode  316  is selected, image scanner  201  knows that the original document contains both text data and image data and therefore, when the block selection process is performed, image scanner  201  will process the text blocks and the image blocks accordingly. As stated above, the invention provides for processing text having a black foreground and a light background as well as text having a light foreground and a dark background.  FIG. 4B  depicts the both types of text data, the former being text data  327  and the latter being text data  329 . 
   Two additional processing modes provided for are photo mode  317  and magazine mode  318 .  FIG. 4C  depicts an example of an original document comprising a photograph for which photo mode  317  may be selected. When photo mode  317  is selected, image scanner  201  is preset to process an original document that contains an image only and does not contain any text. Therefore, the block selection process is not needed since image scanner  201  is set to process only an image and does not detect text data. 
     FIG. 4D  depicts an example of an original document for which magazine mode  318  may be selected. As seen in  FIG. 4D , a magazine type original document may be multilayered in the sense that text data may be included within different background colors. For instance, document  330  of  FIG. 4D  may include text  331  and image  334  on a large blue background  332 , as well as text  335  on a smaller yellow background  333 . To detect such a multilayered document, selecting magazine mode  318  causes image scanner  201  to first detect the large blue background area  332  and then to detect the smaller yellow background area  333 . Thus, utilizing magazine mode  318  of the present invention reduces the misjudgment of text and images in multilayered magazine type original documents. 
   Returning to  FIG. 1 , in printer  200 , each image signal of M, C, Y, and BK from image scanner  201  is sent to laser driver  212 . Laser driver  212  drives semi-conductor laser  213  by signals modulated on the basis of the image signals. The laser beam scans electrostatic drum  217  via polygon mirror  214 , f-θ lens  215 , and mirror  216 . 
   The developer unit is composed of magenta developer  219 , cyan developer  220 , yellow developer  221 , and black developer  222 . These four drums touch electrostatic drum  217 , are configured to turn therewith, and develop latent images of M, C, Y and Bk formed on electrostatic drum  217  with the corresponding color toner. Further, transfer drum  223  attracts a paper sheet fed from paper cassette  224  or  225 , and a toner image developed on electrostatic drum  217  is transferred onto the paper sheet. The paper sheet is then ejected after passing through fixing unit  226 . 
     FIG. 2  is a block diagram showing an image processing flow according to the present invention. As shown in  FIG. 2 , image signals output from a CCD are input to analog signal processing unit  101 , wherein the signal is processed with gain and offset adjustment. Next, each of the R, G and B signals is converted into an 8-bit digital image signal, R 1 , G 1 , and B 1 , respectively, by A/D converter  102 . These signals are then input to shading correction circuit  103  for application of shading correction to each signal. Line delay circuits  104  and  105  are used to compensate for spacing of sensors within the CCD so as to match timing between each of the R 1 , G 1  and B 1  signals such that, after line delay circuit  105 , values of the R, G and B signals at a same point in time represent a same pixel. 
   Input masking unit  106  converts a reading color space, determined by color decomposition characteristics of the CCD, into a standard color space, and log converter  107  converts luminance signals R 4 , G 4  and B 4  into density signals C 0 , M 0  and Y 0 . The density signals are delayed by line delay memory  108  until determination signals UCR (under color removal), FILTER and SEN can be generated. 
   After delay of the signals by line delay memory  108 , masking UCR circuit  109  extracts black signals from the density signals using the UCR signal and variable magnification circuit  110  expands and compresses an image signal and a black character determination signal in the main scanning direction. Space filter processing unit  111  performs filtering using the FILTER signal and the resulting frame-sequential image signals M 4 , C 4 , Y 4  and Bk 4  are sent to reproduction engine  112  along with the SEN signal, which determines the resolution at which the image is output. 
   The UCR, FILTER and SEN signals are output from black character determination unit  115 . Specifically, the UCR signal generated by black character determination unit  113  has a value from 0 to 7 indicating, from more black to less black, an amount of black component which should be removed from signals Y 1 , M 1  and C 1  by masking UCR circuit  109  to produce signal Bk 2 . The FILTER signal produced by black character determination unit  113  is a 2-bit value in which values 0, 1, 2 and 3 indicate smoothing, strong edge enhancement, medium edge enhancement, and weak edge enhancement, respectively. Accordingly, the FILTER signal is input to space filter processing unit  111  to control an amount and type of filtering applied to signals Y 3 , M 3 , C 3  and Bk 3 . 
   The SEN signal is output from black character determination unit  113  to reproduction engine  112 , and is a 1-bit signal in which a 0 value indicates to engine  112  that printing should proceed at 200 lines per inch resolution, and the value 1 indicates that 400 lines per inch printing is required. 
   The values of UCR, FILTER and SEN are outputs of look-up table (LUT)  117 , which receives signals indicating a width of a character containing a subject pixel, a proximity of the subject pixel to an edge of a character, and a chromaticity of the subject pixel. Therefore, the output values of UCR, FILTER, and SEN are calculated for each subject pixel and are determined based on a detected character width, edge proximity and chromaticity corresponding to the pixel according to relationships specified by the LUT. 
   For example, a FILTER signal value of 1 is used for a subject pixel which is located near to an edge and is within a small, black character. In another example, the SEN signal is assigned a value of 0 (corresponding to 200 lines per inch resolution) in a case that the subject pixel is not near an edge and is included in a very thick area, since larger toner dots, which provide more toner per unit area than larger dots, generate a better halftone image. 
   Block selection unit  114  outputs signals representative of font size and attribute. Although block selection unit  114  appears in  FIG. 2  as a hardware unit, it should be noted that the block selection processing described herein and in the applications incorporated by reference herein may be embodied in software or in a combination of software and hardware. Moreover, block selection unit  114  need not be an element of black character determination unit  113 . 
   In operation, block selection unit  114  performs block selection processing on input image data to determine a font size of text in the data as well as attributes of objects within the data. More particularly, for each pixel in input image data, block selection unit  114  assigns a font size of text, if any, in which the pixel is located and an attribute for an object in which the pixel is located. 
   LUT  117  takes as input signals font size, attribute, edge and col, and outputs signals UCR, FILTER and SEN. The detailed contents of LUT  117  are described in more detail in co-pending U.S. patent application Ser. No. 09/458,941, entitled “Block Selection-Based Image Processing”, filed Dec. 10, 1999, the contents of which are incorporated by reference as set forth in full herein. 
     FIG. 5  depicts process steps for performing an image process in a color digital copier according to the invention. In step S 501 , image scanner  201  performs a low resolution scan of an original document and stores the scanned data. The low resolution scanned data is then subjected to a block selection process (step S 502 ) to detect the various type of data contained in the original document and to assign attributes to the blocks. That is, the block selection process detects and identifies blocks of text data and blocks of image data and assigns attributes to each block. The block selection process may be similar to that described in co-pending U.S. patent application Ser. No. 09/458,941, entitled “Block Selection-Based Image Processing”, or any other type of block selection process that identifies text, including edge portions, as well as image data. 
   In step S 503 , a text color detection process is performed on the text blocks. That is, the text blocks detected in the block selection process of step S 502  are subjected to the text color detection process of step S 503 .  FIG. 6  depicts process steps for the color detection process of step S 503 . In step S 601 , the color detection process collects the red (R), green (G) and blue (B) data read by the CCD in the low resolution scan of step S 501  for each pixel in the text character. The edge portions of the text characters detected in the block selection process are discarded (step S 602 ) from the remainder of the color detection process and only the remaining interior pixels of the text character are processed. The RGB values of the remaining interior pixels of the text characters are converted to color space values, such as Lab color space (step S 603 ). The converted color space values for each text character are averaged (step S 604 ) to calculate an average color space value for each text character. In step S 605 , and the average value of each text character is compared to a threshold value. If the average color space value of the text character is below the threshold (determination made in step S 606 ), then the text character is detected as black data (step S 607 ). If the average color space value of the text character is above the threshold, then the text character is detected as color text (step S 608 ). Where the text data is detected as black, then a process to apply only black toner to the text data can be performed and processes to sharpen the text data can also be applied. 
   As can be seen from the process steps of  FIG. 6 , the text color detection process detects the color of the text character on a character by character basis. This in contrast to conventional methods which process text characters on a pixel by pixel basis. That is, in conventional text color detection processes, the process determines whether each pixel in the text character is black or not. Such conventional processes may result in some of the pixels in a single text character being detected as being black, while other pixels in the same text character being detected as low saturation color text. This color detection process results in artifacts being depicted in the text characters due to the discrepancy in the color detection process. In contrast, the text color detection process of the present invention determines color space values for all of the interior pixels in the text character (discarding the edge portions), then averages the color space values of the interior pixels to arrive at an average color space value for the entire text character. Then, utilizing the average color space value, the present invention detects whether the entire character is black or not. Thus, if the character is detected as being black, each pixel in the text character will be processed as a black pixel and therefore artifacts that occur in the conventional process are removed. 
   Returning to  FIG. 5 , after the color detection process of step S 503 , a second high resolution scan is performed for the copying process (step S 504 ). Then, in step S 505 , a color conversion process is performed to convert the high resolution data from RGB values to CMYK values for printing by printer  200 . Finally, the image is processed and output by printer  200  as described above (step S 506 ). 
   As can be seen from the process steps of  FIG. 6 , a more accurate detection of white text on a black background, such as text data  329  of  FIG. 4B , is provided for since the edge portions are not considered in the text color detection process. Additionally, since the edge portions are discarded, a more accurate detection of the text color in magazine type original documents is provided for since the error caused by the blending of the background image with the edge portions is removed. 
   The present invention may also apply a more intelligent text color detection rule. In this regard, the process steps of  FIG. 6  may include additional steps to compare the detected color of each character in a word with one another. That is, once the process has detected that a character is either color text or black text, additional steps to compare each character in a word with one another for consistency among the letters could be applied. This process comprises performing block selection on a word-by-word basis and comparing the individual characters in the word block with one another. Thus, if individual characters of the word are detected as having different colors (i.e. some letters are detected as black while others are detected as low saturation color), the low saturation color characters can be corrected to be black text so that only black toner is applied to all of the letters in the word. 
   The invention has been described with particular illustrative embodiments. It is to be understood that the invention is not limited to the above-described embodiments and that various changes and modifications may be made by those of ordinary skill in the art without departing from the spirit and scope of the invention.