Abstract:
The present invention is directed to methods and devices to increase the brightness of images in display devices. A white signal component is generated according to an input color signal, comprising primary signal components Red, Green and Blue. The generated white signal component and the primary signal components will be manipulated by methods and devices disclosed in the invention to generate adjusted primary signal components. Then the white signal component and the adjusted primary signal components will form a display signal for displaying brightness controlled images. Compared with the input color signal, the brightness of the display signal is increased while the color saturation thereof is almost kept.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to methods and devices for image processing and more particularly, to methods and devices for brightness control of images in display devices. 
     2. Description of Related Art 
     In a color display monitor or a color television, if a flat-panel display is used, it is easier to increase the screen size. But the brightness of displayed images is decreased in comparison with the use of a cathode-ray tube. To overcome such a drawback, a four-color output device in which a white color component is added to the three primary colors of RGB (Red, Green, and Blue) is employed. The white color component can be obtained by having a white light transmitted or reflected onto a white filter, which increases the overall brightness of the images in display devices. 
     A side effect of adding the white color component to the original three primary colors to increase the brightness of images is the decrease in color saturation. To overcome the side effect, the original three primary colors need to be adjusted, so that when these adjusted RGB colors and the white color component are outputted together, the brightness can be increased while the color saturation is almost kept. 
     SUMMARY OF THE INVENTION 
     Accordingly, one of the aspects of the invention is to provide methods to increase the brightness of images in display devices while the color saturation is almost kept. 
     Another aspect of the invention is to provide image processing devices to increase the brightness of images in display devices while the color saturation is almost kept. 
     The present invention is directed to methods and devices to increase the brightness of images in display devices. A white signal component is generated first according to an input color signal, comprising primary signal components Red, Green and Blue. The primary signal components, which carry image data, are inputted from an external device, such as a host computer, pixel by pixel. The generated white signal component and the primary signal components will be manipulated by methods and devices disclosed in the invention to generate adjusted primary signal components. Then the white signal component and the adjusted primary signal components will form a display signal for displaying brightness controlled images. Compared with the input color signal, the brightness of the display signal is increased while the color saturation thereof is almost kept. 
     A method for controlling brightness of an image comprises steps of: determining a coefficient; generating a white signal component from an input color signal; suppressing the input color signal according to the coefficient and the white signal component, to generate adjusted primary signal components of a display signal; and displaying a brightness controlled color image according to the display signal, which further comprises the white signal component; wherein the coefficient affects brightness of the brightness controlled color image. 
     Another method for controlling brightness of an image comprises steps of: generating a conversion parameter from primary signal components of an input color signal; generating a white signal component according to the primary signal components; generating adjusted primary signal components of a display signal according to the conversion parameter, the white signal component and the primary signal components; and displaying a brightness controlled color image according to the display signal, which further comprises the white signal component. 
     An image processing device related to the invention comprises: a detector, generating a white signal component according to primary signal components of an input color signal; a multiplier, multiplying the white signal component with a coefficient to produce a multiplication result; and a subtracting unit, subtracting the multiplication result from the primary signal components to generate adjusted primary signal components of a display signal, which further includes the white signal component. 
     Another image processing device related to the invention comprises: a detector, generating a white signal component from primary signal components of an input color signal; a non-linear converter, outputting a conversion parameter according to the primary signal components; a multiplying unit, multiplying the primary signal components with the conversion parameter to produce a multiplication result; and a subtracting unit, subtracting the white signal component from the multiplication result to generate adjusted primary signal components of a display signal, which further includes the white signal component. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a block diagram of an image processing device in accordance with a first embodiment of the present invention. 
         FIG. 2  is a block diagram of an image processing device with a non-linear converter in accordance with a second embodiment of the present invention. 
         FIG. 3  is a block diagram of the non-linear converter in accordance with the second embodiment of the present invention. 
         FIGS. 4   a ˜ 4   c  show the input color signal (R/G/B) and the display signal (R″/G″/B″/W) in the image processing device in accordance with the second embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     First Embodiment 
       FIG. 1  is a block diagram of an image processing device in accordance with a first embodiment of the present invention. As shown in  FIG. 1 , the image processing device comprises a minimum value detector  101 , a multiplier  103 , and a subtracting unit  105 . The subtracting unit  105  comprises three subtracters  105   a ˜ 105   c . An input color signal to the device includes primary signal components R (red), G (green) and B (blue). 
     The minimum value detector  101  finds the minimum value from the primary signal components and uses the minimum value to generate a white signal component W. For example, the value of the white signal component W may be equal to the minimum value. 
     The white signal component is multiplied by the multiplier  103  with a predetermined coefficient k to produce a multiplication result. 
     The subtracting unit  105  subtracts the multiplication result from the primary signal components to generate adjusted primary signal components R′, G′ and B′. Wherein the subtracter  105   a  subtracts the multiplication result from the primary signal component R to generate the adjusted primary signal component R′; the subtracter  105   b  subtracts the multiplication result from the primary signal component G to generate the adjusted primary signal component G′; and the subtracter  105   c  subtracts the multiplication result from the primary signal component B to generate the adjusted primary signal component B′. The adjusted primary signal components may be expressed by R′=R−kW, G′=G−kW, and B′=B−kW. Four signal components R′, G′, B′ and W are sent, as a display signal, to a display  107 . 
     TABLE 1 shows the experiment results of the above embodiment when different values of k are used and the comparison of brightness and chrominance of the display signal with the brightness and chrominance of the original input color signal. 
     
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                   
                 NTSC % CIE1976 
                   
               
               
                 k 
                 White (WH) 
                 Black (BL) 
                 CR 
                 WH′/WH 
                 (C) 
                 C′/C 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Display 
                 23.453 
                 0.124 
                 189.137 
                 1.332 
                 33.48 
                 0.874 
               
               
                 Signal 
               
               
                 (R′/G′/B′/W), 
               
               
                 k = 0.1 
               
               
                 Display 
                 22.677 
                 0.143 
                 158.580 
                 1.288 
                 33.22 
                 0.867 
               
               
                 Signal 
               
               
                 (R′/G′/B′/W), 
               
               
                 k = 0.2 
               
               
                 Display 
                 18.969 
                 0.134 
                 141.560 
                 1.078 
                 33.26 
                 0.868 
               
               
                 Signal 
               
               
                 (R′/G′/B′/W), 
               
               
                 k = 0.3 
               
               
                 Display 
                 18.198 
                 0.142 
                 128.155 
                 1.034 
                 33.29 
                 0.869 
               
               
                 Signal 
               
               
                 (R′/G′/B′/W), 
               
               
                 k = 0.4 
               
               
                 Input Color 
                 17.604 
                 0.099 
                 177.818 
                 1 
                 38.31 
                 1 
               
               
                 Signal 
               
               
                 (R/G/B) 
               
               
                   
               
               
                 Wherein: 
               
               
                 k: the predetermined coefficient; 
               
               
                 White (WH): the brightness of a white image; 
               
               
                 Black (BL): the brightness of a black image; 
               
               
                 CR: contrast ratio of White (WH) to Black (BL), i.e. WH/BL; 
               
               
                 WH′/WH: ratio of the brightness of the white image of the display signal to the input color signal; 
               
               
                 NTSC % CIE1976 (C): the chrominance of a signal; and 
               
               
                 C′/C: ratio of the chrominance of the display signal to the input color signal. 
               
             
          
         
       
     
     As seen from TABLE 1, by the above embodiment, the brightness of the display signal, comprising R′, G′, B′ and W, is increased compared with the brightness of the input color signal, comprising only R, G and B, while the chrominance of the display signal may be kept to around 87% of the chrominance of the input color signal. When, for example, k is 0.1, the brightness of the white image of the display signal is 33% higher than the brightness of the white image of the input color signal. 
     Second Embodiment 
       FIG. 2  is a block diagram of an image processing device with a non-linear converter in accordance with a second embodiment of the present invention. As shown in  FIG. 2 , the image processing device comprises a minimum value detector  201 , a non-linear converter  203 , a multiplying unit  205 , and a subtracting unit  207 . The multiplying unit  205  comprises three multipliers  205   a ˜ 205   c . The subtracting unit  207  comprises three subtracters  207   a ˜ 207   c . The input color signal to the device includes primary signal components R (red), G (green) and B (blue). 
     The minimum value detector  201  finds the minimum value from the primary signal components and uses the value to generate the white signal component W. For example, the value of the white signal component W may be equal to the minimum value. 
     The non-linear converter  203  uses the primary signal components to generate a conversion parameter α. 
     The multiplying unit  205  multiplies the primary signal components with the conversion parameter α to produce multiplication results. Wherein the multiplier  205   a  multiplies the primary signal component R with the conversion parameter α to produce a multiplication result αR; the multiplier  205   b  multiplies the primary signal component G with the conversion parameter α to produce a multiplication result αG, and the multiplier  205   c  multiplies the primary signal component B with the conversion parameter α to produce a multiplication result αB. 
     The subtracting unit  207  subtracts the white signal component W from the multiplication results to generate the adjusted primary signal components R″, G″ and B″. Wherein the subtracter  207   a  subtracts the white signal component W from the multiplication result αR to generate R″; the subtracter  207   b  subtracts the white signal component W from the multiplication result αG to generate G″; and the subtracter  207   c  subtracts the white signal component W from the multiplication result αB to generate B″. 
     The adjusted primary signal components may be expressed by R″=αR−W, G″=αG−W, and B″=αB−W. Four signal components R″, G″, B″ and W are sent, as a display signal, to a display  209 . 
     The block diagram of the non-linear converter  203  is shown in  FIG. 3 . The non-linear converter  203  comprises a maximum value detector  301  and a conversion parameter outputting unit  303 . The maximum value detector  301  finds a maximum value from the primary signal components R, G and B. The conversion outputting unit  303  will generate the conversion parameter α by, for example, using the formula, α=[UP/MAX] β , wherein MAX is the maximum value found from the maximum value detector  301 ; UP is the upper limit of the primary signal components, for example, 255; and β is a predetermined coefficient, ranging from 0 to 1 and preferred 0.5. 
     The conversion parameter outputting unit  303  in  FIG. 3  may be implemented by a look-up table (LUT) with a predetermined coefficient β. The LUT provides a one-to-one mapping of its input value from the maximum value detector  301  and its output value, the conversion parameter α. Or the conversion parameter outputting unit  303  may be implemented by multiple look-up tables, each with a different coefficient β. Different coefficients β may be used by multiple LUTs to provide greater flexibility for designers to choose one LUT from multiple LUTs to output the conversion parameter α. 
     The conversion parameter outputting unit  303  in  FIG. 3  may also be implemented by a microprocessor. The microprocessor may calculate the conversion parameter α. The value of the predetermined coefficient β may be changed by designers easily to provide even greater flexibility. 
       FIG. 4   a ˜ 4   c  show the values of the primary signal components R, G and B of the input color signal, the adjusted primary signal components R″, G″ and B″ and the white signal component W at different processing stages in an image processing device in accordance with the second embodiment of the present invention. In  FIG. 4   a , the values of the primary signal components R, G and B are shown, as an example, and the value of the white signal component W is set to be the same as the value of the primary signal component G, the one with the minimum value among the primary signal components R, G and B. In  FIG. 4   b , each of the primary signal components is multiplied by the conversion parameter α to produce αR, αG, and αB. In  FIG. 4   c , the values of the adjusted primary signal components R″, G″ and B″ are shown, wherein R″=αR−W, G″=αG−W, and B″=αB−W. The value 255 on the vertical axis represents the upper limit UP of the primary signal components. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing descriptions, it is intended that the present invention covers modifications and variations of this invention if they fall within the scope of the following claims and their equivalents.