Dynamic contrast on displays using average picture level and histogram analysis

Abstract

Average picture level (APL) of a display and, in examples, histogram information is used to dynamically adjust the display contrast, or “gamma”, using an exponential function. APL can also be used for DC transmission adjustment and black/white stretch.

1 . Display system, comprising:
 video display;   processor circuitry receiving demanded image information and adjusting the demanded image information for output on the display, the processor circuitry executing logic comprising:
 obtaining average picture level (APL) associated with the demanded image; 
 using the APL to alter a gamma associated with the demanded image; 
 using the APL to alter a DC transmission characteristic associated with the demanded image; and 
 using the APL to alter a black stretch and white stretch characteristic associated with the demanded image. 
   
     
     
         2 . The system of  claim 1 , wherein the processor circuitry alters the gamma, then alters the DC transmission characteristic, then alters the black stretch and white stretch characteristic. 
     
     
         3 . The system of  claim 1 , wherein the processor circuitry uses histogram information associated with the demanded image to alter the gamma. 
     
     
         4 . The system of  claim 1 , wherein the gamma is altered using an exponential function. 
     
     
         5 . The system of  claim 4 , wherein the exponential function includes a factor related to the APL. 
     
     
         6 . The system of  claim 5 , wherein the exponential function includes a control factor of the form (first gain plus (user-established dynamic gain factor)) multiplied by a gain from a histogram, wherein the first gain, dynamic gain factor, and gain from a histogram are different from each other. 
     
     
         7 . (canceled) 
     
     
         8 . The system of  claim 1 , wherein the exponential function is 10 −(gain(w)+rate(w))*wgain*index(APL)  for APL higher than the threshold, wherein gain(w) is a second range conversion factor, rate(w) represents a linear relationship between APL and a received gain multiplied by a user-established dynamic gain factor, wgain is a white gain as indicated by the histogram, and index(APL) is a parameter representative of a received APL. 
     
     
         9 . A display system comprising:
 a display; and   a processor circuitry receiving an input signal representing a demanded image for the display and automatically altering a gamma of the input by applying an S-shaped transfer function to the input to produce an output used by the display to present the demanded image.   
     
     
         10 . The system of  claim 9 , wherein a positive exponential gain function is used to establish a portion of the curve below an average picture level (APL) threshold and a negative exponential gain function is used to establish a portion of the curve above the threshold. 
     
     
         11 . The system of  claim 10 , wherein the threshold dynamically changes as the APL of the input signal changes. 
     
     
         12 . The system of  claim 11 , wherein if APL is relatively high, black gain is established to be relatively high and white gain is established to be relatively low, and if APL is relatively low, black gain is established to be relatively low and white gain is established to be relatively high. 
     
     
         13 . The system of  claim 12 , wherein histogram information associated with the input signal is used in the transfer function to establish the output. 
     
     
         14 . The system of  claim 13 , wherein a gain output of the transfer function is inversely proportional to a width of a histogram range distribution of brightness levels. 
     
     
         15 . Machine-implemented method comprising:
 receiving a demanded image for a visual display, an input contrast being associated with the demanded image;   altering the input contrast using at least one exponential function to produce an output contrast;   implementing the output contrast in the demanded image; and   presenting the demanded image on the display.   
     
     
         16 . The method of  claim 15 , wherein the exponential function includes a factor representative of an average picture level (APL) associated with the demanded image. 
     
     
         17 . The method of  claim 15 , wherein the exponential function includes a factor representative of histogram information associated with the demanded image. 
     
     
         18 . The method of  claim 15 , comprising using APL to apply a DC transmission adjustment to the demanded image after altering the input contrast using the exponential function. 
     
     
         19 . The method of  claim 18 , comprising using APL to apply a black/white stretch adjustment to the demanded image after applying the DC transmission adjustment. 
     
     
         20 . The method of  claim 15 , comprising using an S-shaped transfer function including the exponential function to dynamically alter the input contrast.