Patent Document

FIELD OF THE INVENTION 
       [0001]    The invention relates to the field of image processing, and in particular, to color printing systems. 
       BACKGROUND 
       [0002]    When color images are printed in grayscale at a print system, the images undergo a color to gray transformation. Various algorithms exist that are be implemented to convert color to grayscale. The most commonly used method obtains lightness/luminance and disregards chroma/hue information. The drawback of this approach is that colors with the same lightness/luminance, but different chroma/hue, are converted to the same gray value. This is most noticeable and objectionable for a job with a red, green and blue pie chart of similar lightness for instance. 
         [0003]    Another known method incorporates color difference equations into the transformation from color to grayscale. This method involves more color attributes during the conversion than that of the lightness preserving method. However, this method often causes discontinuity or low contrast in some color regions. 
         [0004]    Accordingly, a monochrome profile generation mechanism that preserves perceptual differences in lightness, chroma and hue with smooth transitions when converting color to grayscale is desired. 
       SUMMARY 
       [0005]    In one embodiment, a method includes receiving color data, converting the color data to grayscale data by analyzing color gamut and perceptual color differences in the color data and generating a profile based on the conversion 
         [0006]    In another embodiment, a printer is disclosed. The printer includes a control unit to receive color data, convert the color data to grayscale data by analyzing color gamut and perceptual color differences in the color data and generate a profile based on the conversion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    A better understanding of the present invention can be obtained from the following detailed description in conjunction with the following drawings, in which: 
           [0008]      FIG. 1  illustrates one embodiment of a data processing system network; 
           [0009]      FIG. 2  illustrates one embodiment of a control unit; 
           [0010]      FIG. 3  is a flow diagram illustrating one embodiment for performing color conversion; 
           [0011]      FIG. 4  is a flow diagram illustrating one embodiment for generating a monochrome profile; 
           [0012]      FIGS. 5A, 5B and 5C  illustrate a pie chart implement to illustrate embodiments for generating a monochrome profile; and 
           [0013]      FIG. 6  illustrates one embodiment of a computer system. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    A monochrome profile generation mechanism is described that enables colors with different lightness to be distinguishable, as well as the colors with the same lightness and different chroma/hue to be discernible. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some of these specific details. In other instances, well-known structures and devices are shown in block diagram form to avoid obscuring the underlying principles of the present invention. 
         [0015]    Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment. 
         [0016]      FIG. 1  illustrates one embodiment of a printing system  100 . Printing system  100  includes a print application  110 , a server  120  and printer  130 . Printer  130  includes a control unit  150  and a print engine  160 . Print application  110  makes a request for the printing of a document. In one embodiment, print application  110  provides data in the form of a page description language (PDL) (e.g., Advanced Function Presentation (AFP), PostScript (PS), Portable Document Format (PDF), etc.) file for printing to print server  120 . 
         [0017]    According to one embodiment, control unit  150  processes and renders objects received from print server  120  and provides raster maps for printing to print engine  160 .  FIG. 2  illustrates one embodiment of a control unit  150 . Control unit  150  includes a rasterizer  200  having color management unit  210 , as well as other units that will not be described herein. 
         [0018]    Rasterizer  200  is implemented to process image objects received at control unit  150  by performing a raster image process (RIP) to convert an image described in a vector graphics format (e.g., shapes) into a raster image (e.g., pixels) for output to print engine  160 . Color management unit  210  provides a color mapping from a source to a destination color space. 
         [0019]    In such an embodiment, color management unit  210  uses ICC profiles to perform the mapping to determine CMYK values for each pixel in a particular object to be printed at print engine  160 . Further, color management unit  210  may convert a print job file from an input color space to printer device space using an input ICC profile and printer ICC profile. 
         [0020]    According to one embodiment, color management unit  210  includes monochrome mapping unit  220  provides color conversion mapping of a print job to black and white. Thus, monochrome mapping unit  220  implements a monochrome printer profile to enable the color conversion of a print job in any color space to black and white. In a further embodiment, monochrome mapping unit  220  performs the color conversion mapping based on an operator selecting a monochrome mode via a Graphical User Interface (GUI)  170  at printer  130 . 
         [0021]    In one embodiment, monochrome mapping unit  220  optimizes color to grayscale conversion by taking into account color gamut and perceptual color differences. In such an embodiment, monochrome mapping unit  220  maps colors to a desired color gamut, compresses chroma and lightness to the most visible and differentiable ranges, maximizes color differences in hue and the most sensitive areas in perception and optimizes the conversion with different weighting functions of a combination of lightness, chroma and hue. 
         [0022]      FIG. 3  is a flow diagram illustrating one embodiment for performing color conversion in a print file. Process  300  may be performed by processing logic that may comprise hardware (e.g., circuitry, dedicated logic, programmable logic, etc.), software (such as instructions run on a processing device), or a combination thereof. In one embodiment, method  300  may be performed by control unit  150 . The processes of method  300  are illustrated in linear sequences for brevity and clarity in presentation; however, it is contemplated that any number of them can be performed in parallel, asynchronously, or in different orders. For brevity, clarity, and ease of understanding, many of the details discussed with reference to  FIGS. 1 and 2  are not discussed or repeated here. 
         [0023]    At processing block  310 , a print job file is received at control unit  150 . At block  320 , it is determined whether monochrome mode is enabled. In one embodiment, the monochrome mode may be enabled or disabled by the operator at GUI  170 . If the monochrome mode is not enabled, color management unit  210  performs color mapping to convert the color of each pixel of the received image to a corresponding output color based on the selected ICC printer profiles, processing block  330 . However if the monochrome mode is enabled, monochrome mapping unit  220  performs the mapping, processing block  340 . 
         [0024]      FIG. 4  is a flow diagram illustrating one embodiment a process  400  for performing color to grayscale conversion in order to achieve monochrome mapping. Process  400  may be performed by processing logic that may comprise hardware (e.g., circuitry, dedicated logic, programmable logic, etc.), software (such as instructions run on a processing device), or a combination thereof. In one embodiment, method  400  may be performed by monochrome mapping unit  220 . The processes of method  400  are illustrated in linear sequences for brevity and clarity in presentation; however, it is contemplated that any number of them can be performed in parallel, asynchronously, or in different orders. For brevity, clarity, and ease of understanding, many of the details discussed with reference to  FIGS. 1-3  are not discussed or repeated here. 
         [0025]    At processing block  410 , color data is received. At processing block  420 , color range compression is performed. In one embodiment, color range compression includes gamut compression, lightness compression and chroma compression in order to create sufficient spaces for more used colors. Lightness is a property of a color (or a dimension of a color space) that is defined in a way to reflect a subjective brightness perception of a color for humans along a lightness-darkness axis. Chroma is a perceived colorfulness in proportion to the brightness of a reference white patch. 
         [0026]    In one embodiment, L, a*,b* grid points are mapped into a gamut of a standard RGB (sRGB) color space, and coordinates are changed to (L*, c*, h*). Subsequently, L is scaled by an scaling curve (S-curve), such that: 
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         [0027]    After L scaling, C is scaled by an increasing curve such that: 
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         [0028]    In one embodiment, the scaling of L and C may be performed manually. At processing block  430 , color difference is assessed. In one embodiment the assessment includes lightness, chrome and hue. Hue is defined as a degree to which a stimulus can be described as similar to or different from stimuli that are described as red, green, blue, and yellow (e.g., the unique hues). 
         [0029]    According to one embodiment, greater lightness (e.g., higher L value) colors correspond to less black in human eye. Monochrome level correspondence for different chroma may be complicated. Thus, given color patches with the same lightness, same hue angle, but with different chrome values, observers may have different opinions regarding which color appears to be blacker or whiter. Thus embodiments where larger—chroma values are chosen will result in “whiter” color. 
         [0030]    Psychological experiments show that for high lightness and low lightness regions, monochrome level correspondence for different hue angles is different. Thus, embodiments feature two different hue weighting functions, which rely on human responses with different hue angle colors. In such an embodiment, one weighting function is implemented for L&gt;L 0  and a second weighting function is implemented for L&lt;L 0 . 
         [0031]    Hue weighting for high lightness (L≦30) corresponds to: 
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         [0032]    Similarly, hue weighting for high lightness (L&gt;30) corresponds to: 
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         [0033]    At processing block  440 , a model is built. According to one embodiment, an output function will determine the K values that will be written in a look up table in the monochrome profile. In such an embodiment, the output function is represented by: 
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         [0034]    As discussed above, the L and C values have been scaled in processing block  430 . Wt_H is the hue weighting function defined with hue angle as input, while wLo is a weighing function with lightness as input. The remaining parameters (a, b, c, d, e, wC and wH) are to be determined by generating training data by using wt=L+wL 0 *wt_H*C. Subsequently, the parameters are optimized using a nonlinear least square fit algorithm. This approach enables the use of any specified training data to obtain the optimized parameters that correspond to the data. 
         [0035]      FIGS. 5A, 5B and 5C  illustrate a pie chart implement to illustrate embodiments for generating a monochrome profile.  FIG. 5A  illustrates a color version of the pie chart showing red, green and blue components.  FIG. 5B  illustrates a grayscale version of the pie chart in which convention color to grayscale has been performed. As shown in  FIG. 5B , the grayscale components corresponding to each pie chart color are indistinguishable.  FIG. 5C  illustrates a grayscale version of the pie chart performed by method  400 . As shown in  FIG. 5C , the grayscale components corresponding to each pie chart color is distinguishable, which permits analysis of a grayscale version of the pie chart. 
         [0036]      FIG. 6  illustrates a computer system  600  on which server  120  and/or printer  130  may be implemented. Computer system  600  includes a system bus  620  for communicating information, and a processor  610  coupled to bus  620  for processing information. 
         [0037]    Computer system  600  further comprises a random access memory (RAM) or other dynamic storage device  625  (referred to herein as main memory), coupled to bus  620  for storing information and instructions to be executed by processor  610 . Main memory  625  also may be used for storing temporary variables or other intermediate information during execution of instructions by processor  510 . Computer system  600  also may include a read only memory (ROM) and or other static storage device  626  coupled to bus  620  for storing static information and instructions used by processor  610 . 
         [0038]    A data storage device  625  such as a magnetic disk or optical disc and its corresponding drive may also be coupled to computer system  600  for storing information and instructions. Computer system  600  can also be coupled to a second I/O bus  650  via an I/O interface  630 . A plurality of I/O devices may be coupled to I/O bus  650 , including a display device  624 , an input device (e.g., an alphanumeric input device  623  and or a cursor control device  622 ). The communication device  621  is for accessing other computers (servers or clients). The communication device  621  may include a modem, a network interface card, or other well-known interface device, such as those used for coupling to Ethernet, token ring, or other types of networks. 
         [0039]    Embodiments of the invention may include various steps as set forth above. The steps may be embodied in machine-executable instructions. The instructions can be used to cause a general-purpose or special-purpose processor to perform certain steps. Alternatively, these steps may be performed by specific hardware components that contain hardwired logic for performing the steps, or by any combination of programmed computer components and custom hardware components. 
         [0040]    Elements of the present invention may also be provided as a machine-readable medium for storing the machine-executable instructions. The machine-readable medium may include, but is not limited to, floppy diskettes, optical disks, CD-ROMs, and magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, magnetic or optical cards, propagation media or other type of media/machine-readable medium suitable for storing electronic instructions. For example, the present invention may be downloaded as a computer program which may be transferred from a remote computer (e.g., a server) to a requesting computer (e.g., a client) by way of data signals embodied in a carrier wave or other propagation medium via a communication link (e.g., a modem or network connection). 
         [0041]    Whereas many alterations and modifications of the present invention will no doubt become apparent to a person of ordinary skill in the art after having read the foregoing description, it is to be understood that any particular embodiment shown and described by way of illustration is in no way intended to be considered limiting. Therefore, references to details of various embodiments are not intended to limit the scope of the claims, which in themselves recite only those features regarded as essential to the invention.

Technology Category: 5