Image Range Expansion Control Methods and Apparatus

Abstract

Image data is adjusted for display on a target display. Maximum safe expansions for one or more attributes of the image data are compared to maximum available expansions for the attributes. An amount of expansion is selected that does not exceed either of the maximum safe expansion and the maximum available expansion. Artifacts caused by over expansion may be reduced or avoided.

1 . A method for image processing, the method comprising:
 obtaining image data and metadata associated with the image data;   processing the metadata with information characterizing a target display to determine a maximum safe expansion for an attribute of the image data and a maximum available expansion for the attribute of the image data; and,   processing the image data to expand the attribute of the image data by the lesser of the maximum safe expansion and the maximum available expansion.   
     
     
         2 . A method according to  claim 1  wherein the attribute is dynamic range and processing the image data comprises applying a tone mapping curve to the image data. 
     
     
         3 . A method according to  claim 2  wherein the metadata comprises metadata indicative of a bit depth of the image data and the method comprises determining the maximum safe expansion based at least in part on the bit depth. 
     
     
         4 . A method according to  claim 3  wherein the metadata comprises metadata indicative of an encoding quality level of the image data and the method comprises determining the maximum safe expansion based at least in part on the encoding quality level. 
     
     
         5 . A method according to  claim 3  wherein determining the maximum safe expansion comprises using the bit depth as a key to look up a value for the maximum safe expansion in a lookup table. 
     
     
         6 . A method according to  claim 2  wherein the metadata comprises metadata indicative of a dynamic range of a source display and determining the maximum available expansion comprises computing a ratio of a dynamic range of the target display and the dynamic range of the source display. 
     
     
         7 . A method according to  claim 1  wherein the attribute comprises a color gamut. 
     
     
         8 . A method according to  claim 1  wherein the metadata comprises metadata directly indicative of the maximum safe expansion. 
     
     
         9 . A method according to  claim 8  wherein the attribute is one of a plurality of attributes and the metadata comprises metadata directly indicative of the maximum safe expansion for each of the plurality of attributes. 
     
     
         10 . A method according to  claim 9  wherein the plurality of attributes comprises dynamic range and color gamut. 
     
     
         11 . Image processing apparatus comprising:
 a decoder configured to extract image data and metadata associated with the image data from a signal;   a controller configured to process the metadata with information characterizing a target display to determine a maximum safe expansion for an attribute of the image data and a maximum available expansion for the attribute of the image data and to set an expansion amount equal to the smaller of the maximum safe expansion and the maximum available expansion; and   an expander configured to expand the attribute of the image data by the expansion amount to yield modified image data.   
     
     
         12 . Apparatus according to  claim 11  integrated with the target display wherein the target display is connected to display the modified image data. 
     
     
         13 . Apparatus according to  claim 12  wherein the target display comprises a television or a digital cinema projector. 
     
     
         14 . Apparatus according to  claim 11  comprising an interface for data communication with the target display wherein the controller is configured to access the information characterizing the target display by way of the interface.