Abstract:
A method and an arrangement for improving the digital-signal-generated grayscale resolution of a monochrome visual display unit ( 3 ) to which the digital signals from an image source ( 1 ) can be supplied over n-bit wide RGB channels ( 2 ). Measures are proposed that make it possible to display distinguishable grayscale gradations on the visual display unit ( 3 ) regardless of whether a grayscale signal ( 6; 10 ) or RGB color signals ( 12, 13, 14 ) are transmitted to the visual display unit ( 3 ).

Description:
[0001]    This application claims priority under 35 U.S.C. §119(a) to German Patent Application No. 10 2007 025 504.9, filed on Jun. 1, 2007, the entire contents of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a method and arrangement for improving the digital-signal-generated grayscale resolution of a monochrome visual display unit to which the digital signals from an image source can be supplied over an n-bit wide RGB wire pair. 
         [0004]    2. Description of the Related Art 
         [0005]    In the medical field, monochrome visual display units, which must meet very high requirements in terms of grayscale resolution, are used particularly to interpret X-ray images. For this type of use, monochrome visual display units are superior to color units. The current requirements in terms of grayscale resolution call for 10-bit wide grayscale signals, enabling 1024 grayscale gradations on a monochrome visual display unit. 
         [0006]    If such a monochrome visual display unit is connected to a 24-bit color-image source by a DVI cable (Digital Video Interface cable), which has one wire pair for each 8-bit wide RGB channel, it is not possible to visually represent all the RGB color information transmitted to the monochrome visual display unit in a “correct” grayscale on that visual display unit. This means that information is lost, which can have a disturbing effect on a viewer. For example, RGB signals with color information (0, 255, 0), (255, 255, 0) or (0, 255, 255), which a color visual display unit displays as the colors green, yellow and turquoise, appear white on a monochrome visual display unit. 
       SUMMARY OF THE INVENTION 
       [0007]    An aspect of the present invention is to provide a method and arrangement of the above-described type, which displays distinguishable grayscale gradations on a monochrome visual display unit regardless of whether a grayscale signal or RGB color signals are transmitted to that monochrome visual display unit. 
         [0008]    According to one formulation, the method includes generating n-bit-wide RGB color signals for transmission of an input m-bit-wide grayscale signal with an encoding device of the image source and generating an output m-bit-wide grayscale signal from the received n-bit-wide RGB color signals with a decoding device of the visual display unit. According to a further formulation, the arrangement includes a monochrome visual display unit, an image source, which supplies digital signals to the monochrome visual display unit over n-bit-wide RGB channels, an encoding device of the image source generating n-bit-wide RGB color signals for transmission of an input m-bit-wide grayscale signal and a decoding device of the visual display unit for generating an output m-bit-wide grayscale signal from the received n-bit-wide RGB color signals. 
         [0009]    The advantage is that no color information is lost and for each piece of color information, a grayscale gradation is displayed on the monochrome visual display unit that corresponds to that piece of color information. 
         [0010]    Advantageous embodiments of the invention are set forth in the dependent claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Embodiments and advantages of the invention will now be described in greater detail with reference to non-limiting embodiments depicted in the drawings, in which: 
           [0012]      FIG. 1  schematically shows an arrangement with an image source and a monochrome visual display unit, and 
           [0013]      FIGS. 2 and 3  illustrate process steps for encoding and decoding a digital signal. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0014]    An image source  1  in the form of a personal computer with a suitable graphics card is connected to a monochrome visual display unit  3  in the form of an LCD display module by means of a DVI cable  2 , which is known in the art. The DVI cable  2  has three 8-bit wide RGB channels over which the image source  1  transmits a digital RGB signal to the monochrome visual display unit  3 . 
         [0015]    An image source  1  runs an application program  4  to process and display a black and white X-ray image and a Windows application  5  to display, for example, icons on the visual display unit  3 . The Windows application generates digital RGB color information, which the image source  1  transmits via an encoding device  7  to the visual display unit  3  in the form of 8-bit wide RGB signals. In contrast, the application program  4  generates a 10-bit wide grayscale signal  6 . The encoding device  7  of the image source  1  processes this grayscale signal  6  as well as the 8-bit wide RGB signals and supplies them to a decoding device  8  of the visual display unit  3  over the three 8-bit wide RGB channels of the cable  2 . The decoding device  8  processes the signals transmitted by the encoding device  7  and generates a 10-bit wide grayscale signal  9  to display corresponding monochrome image information on a display of the visual display unit  3 . 
         [0016]    To make it possible to display distinguishable grayscale gradations on the visual display unit  3  regardless of whether a grayscale signal or an RGB color signal is transmitted to the visual display unit  3  over the RGB channels, the signals are suitably processed by the encoding and decoding devices. In the following we refer to  FIGS. 2 and 3 , which illustrate an encoding and decoding of a grayscale signal or of RGB color signals. 
         [0017]    An encoding device processes a 10-bit wide grayscale signal  10  generated by an application program in such a way that the encoding device uses, respectively, seven bit locations D 3 , D 4 , . . . D 9  with associated bit values of the grayscale signal  10  and, further, one of the bit locations D 0 , D 1 , D 2  of the grayscale signal  10  with associated bit value to form an RGB signal ( FIG. 2 ). This means that the bit values of the bit locations R 7 , R 6 , . . . , R 1  of the R signal, the bit values of the bit locations G 7 , G 6 , . . . , G 1  of the G signal and, further, the bit values of the bit locations B 7 , B 6 , . . . , B 1  of the B signal match and only the respective bit value of the bit locations R 0 , G 0 , B 0  differ. In the present example, the encoding device generates an R signal “01111111,” a G signal “01111110” and a B signal “01111111” and transmits the R signal over the R channel, the G signal over the G channel and the B signal over the B channel of a decoding device of a visual display unit, which uses these RGB color signals to generate a grayscale signal  11 . 
         [0018]    The decoding of RGB color information in the form of 8-bit wide RGB color signals  12 ,  13 ,  14  ( FIG. 3 ) will now be discussed in detail. It is assumed that a Windows application supplied the RGB color signals  12 ,  13 ,  14  to an encoding device, and the encoding device transmitted these signals  12 ,  13 ,  14  to a decoding device over RGB channels. The decoding device uses these RGB color signals  12 ,  13 ,  14  to generate a grayscale signal  20  by first generating a respective reference value, for example, in the form of a color decimal value FR, FG, FB, from the bit values  15  of the bit locations R 7 , R 6 , . . . , R 1 , the bit values  16  of the bit locations G 7 , G 6 , . . . , G 1  and the bit values  17  of the bit locations B 7 , B 6 , . . . , B 1 . In the present example, the resulting decimal color values are FR=127, FG=127 and FB=0. The decoding device adds these decimal color values FR, FG, FB using weighted addition, according to the following formula: 
         [0000]    
       
      
       Y=a*FR+b*FG+c*FB  
      
     
         [0000]    to form the associated binary value DW. In a practical example of the invention, the factor a is selected as 2/8, the factor b as ⅝ and the factor c as ⅛, so that the result of the weighted addition Y is the decimal number 111. The associated binary number DW is 1101111, the bit combination of which forms the bit values  18  of the seven bit locations D 9 , D 8 , . . . , D 3  of the 10-bit wide grayscale signal  20  to be generated. These seven bit values  18  are supplemented by the respective bit values  19  of the bit locations R 0 , G 0 , B 0 , such that the grayscale signal  20  is generated by decoding the RGB color signal  12 ,  13 ,  14 . 
         [0019]    The decoding device decodes the RGB color signals according to  FIG. 1  in the same manner and generates the grayscale signal  11 , which corresponds to the grayscale signal  10  from which the encoding device generated the RGB color signals. 
         [0020]    The above description of the preferred embodiments has been given by way of example. From the disclosure given, those skilled in the art will not only understand the present invention and its attendant advantages, but will also find apparent various changes and modifications to the structures and methods disclosed. The applicant seeks, therefore, to cover all such changes and modifications as fall within the spirit and scope of the invention, as defined by the appended claims, and equivalents thereof.