High dynamic range image signal generation and processing

Abstract

An apparatus generates an image signal in which pixels are encoded in N-bit words which encode at least a luma per pixel. A receiver ( 201 ) obtains high dynamic range pixel values in accordance with a first color representation in M-bitwords. A first generator ( 203 ) includes the high dynamic range pixel values in the image signal in the N-bit words according to a second color representation. A second generator ( 205 ) includes in the image signal an indicator that high dynamic range pixel values are encoded. In some examples, the high dynamic range pixel values may be provided in a segment that can alternatively contain high or low dynamic range pixel values, and the indicator may indicate which type of data is included. The approach may e.g. facilitate introduction of high dynamic range capability into e.g. HDMI systems.

The invention claimed is: 
     
       1. An apparatus for generating an image signal in which pixels are encoded in N-bit words, the apparatus comprising:
 a memory; 
 at least one processor circuit coupled to the memory, wherein the at least one processor being circuit is configured to: 
 decode receivedreceive high dynamic range pixel values; 
 store the high dynamic range pixel values in the memory, wherein the high dynamic range pixel values are arranged in accordance with a first color representation in M-bit words; 
 encode the high dynamic range pixel values in into the image signal of N-bit words according to a second color representation; and 
 compute an indicator in the image signal of a type of high dynamic range encoding, wherein the indicator is transmitted for specifying which high dynamic range pixel values are encoded and how the high dynamic range pixel values are transformed for display comprises a luminance at which a maximum luma code is to be displayed; and 
 output the image signal, wherein the image signal comprises the encoded high dynamic range pixel values and the indicator. 
 
     
     
       2. The apparatus of  claim 1 , wherein the first color representation is different from the second color representation. 
     
     
       3. The apparatus of  claim 2 , wherein the at least one processor circuit is further configured to transform the high dynamic range pixel values from the first color representation to the second color representation. 
     
     
       4. The apparatus of  claim 2 ,
 wherein the high dynamic range pixels comprise M-bit words, 
 wherein the encoded pixels comprise N-bit words  
 wherein the at least one processor circuit is further configured to compress M-bit words into N-bit words, where M is larger than N. 
 
     
     
       5. The apparatus of claim  4  1, wherein the at least one processor circuit is further configured to use a different quantization scheme for the pixel values in accordance with the second color representation than for the pixel values in accordance with the first color representation to compress the M-bit words into the N-bit words. 
     
     
       6. The apparatus of  claim 1 , wherein the first color representation is the same as the second color representation. 
     
     
       7. The apparatus of  claim 1 , wherein the indicator comprises an indication of a peak white of the second color representation. 
     
     
       8. The apparatus of  claim 1 ,
 wherein the indicator specifies a distribution of luma or color values, 
 along a rangewherein the distribution describes a mapping of a first set of codeable colors in the M-bitfirst color representation alongto a second set of codeable range of the N-bit signalcolors in the second color representation. 
 
     
     
       9. The apparatus of  claim 1 ,
 wherein the first color representation employs comprises a separate color value for each color component of the first color representation, and 
 wherein the second color representation employscomprises a set of color values for each color component of the second color representation together with a common exponential factor. 
 
     
     
       10. The apparatus of  claim 1 ,
 wherein the image signal comprises a segment,  
 forwherein the segment comprises pixel image data, and 
 wherein the at least one processor circuit is further configured to alternatively either include low dynamic range pixel values, or the high dynamic range pixel values according to the second color representation in the segment, and 
 wherein the indicator specifies whether a firstthe segment comprises low dynamic range color values or high dynamic range color values. 
 
     
     
       11. The apparatus of claim  10  1,
 wherein the at least one processor circuit is further configured to include a second indicator in the image signals signal, 
 wherein the second indicator statingindicates that the segmentimage signal is encoding low dynamic range pixel values both when the segment image signal comprises low dynamic range pixel values and when the segment comprises high dynamic range pixel values. 
 
     
     
       12. The apparatus of  claim 1 , wherein the at least one processor circuit is further configured to include the high dynamic range pixel values in a Deep Color data segment according to an HDMI standard. 
     
     
       13. The apparatus of  claim 1 , wherein the at least one processor circuit is further configured to include the indicator in an Auxiliary Video Information InfoFrame. 
     
     
       14. A method of generating an image signal in which pixels are encoded in N-bit words, the method comprising:
 decoding receivedreceiving high dynamic range pixel values in accordance with a first color representation in M-bit words; 
 encoding the high dynamic range pixel values in the image signal of N-bit words according to a second color representation; and 
 computing an indicator in the image signal of a type of high dynamic range encoding, 
 wherein the indicator is transmitted for specifying which high dynamic range pixel values are encoded and how the high dynamic range pixel values are transformed for display comprises a luminance at which a maximum luma code is to be displayed; and 
 transmitting the image signal and the indicator. 
 
     
     
       15. An apparatus for processing an image signal, the apparatus comprising:
 a memory; 
 at least one processor circuit coupled to the memory, wherein the at least one processor being circuit is configured to:
 receive the image signal, a data segment of the image signal comprising one of 
 wherein the image signal comprises high dynamic range pixel values in N-bit wordsencoded according to a firstsecond color representation and,  
 low dynamic range pixel values according to a second color representation, and for receiving 
 wherein the image signal comprises an indicator indicative of a type of high dynamic range encoding of the high dynamic range pixel values, 
 wherein the indicator specifies which high dynamic range pixel values are encoded and how the high dynamic range pixel values are to be transformed for display 
 wherein the indicator comprises a luminance at which a maximum luma code is to be displayed; 
 extract data of the data segment; and 
 process the data of the data segment as high dynamic range pixel values dependent on the value of the indicator image signal according to the luminance at which a maximum luma code is to be displayed. 
 
 
     
     
       16. The apparatus as claimed in  claim 15 , wherein at least one processor circuit is configured to map the N-bit words high dynamic range pixel values to display renderable output signals in dependence on a coding used in the N-bit words as indicated by the indicator. 
     
     
       17. The apparatus as claimed in  claim 15 ,
 wherein the at least one processor circuit is configured to apply a color transformation implementing at least a mapping of grey values along a first luminance range associated with the N-bit words, first color representation to a second third luminance range, 
 wherein the third luminance range is associated with a display, 
 in whichwherein the color transformation is dependent on a peak white, or any white level indication characterizing a scene luminance level of the maximum luminance codeable with the N-bits wordsthe luminance at which a maximum luma code is to be displayed. 
 
     
     
       18. The apparatus of  claim 15 ,
 wherein the image signal is in accordance with an HDMI standard, and the at least one processor is further configured to transmit an indication of a capability to process high dynamic range pixel values in an HDMI vendor specific data block. 
 
     
     
       19. A method of processing an image signal, the method comprising:
 receiving the image signal, a data segment of the image signal comprising one of high dynamic range pixel values in N-bit words according to a first second color representation and low dynamic range pixel values according to a second color representation; 
 receiving an indicator indicative of a type of high dynamic range encoding that specifies which high dynamic range pixel values are encoded and how the high dynamic range pixel values are transformed for display, wherein the indicator comprises a luminance at which a maximum luma code is to be displayed; and 
 processing the data of the data segment as high dynamic range pixel values or as low dynamic range pixel values dependent based on the value of the luminance at which a maximum luma code is to be displayed as indicated in the indicator. 
 
     
     
       20. A method of processing an image signal as claimed in claim 19, wherein the high dynamic range pixel values are received in N-bit words, and wherein the method comprises mapping the N-bit words to display renderable output signals in dependence on a coding used in the N-bit words as indicated by the indicator. 
     
     
       21. A method of processing an image signal as claimed in claim 19, further comprising applying a color transformation implementing at least a mapping of grey values along a first luminance range associated with the first color representation to a third luminance range,
 wherein the third luminance range is associated with a display,   wherein the color transformation is dependent on the luminance at which a maximum luma code is to be displayed.   
     
     
       22. The method of generating an image signal as claimed in claim 14, further comprising including a second indicator in the image signals, wherein the second indicator specifies that the image signal is encoding low dynamic range pixel values when the image signal comprises the high dynamic range pixel values. 
     
     
       23. The apparatus of claim 1, wherein the indicator specifies which type of the high dynamic range pixel values are encoded. 
     
     
       24. The method of claim 14, wherein the indicator specifies which type of the high dynamic range pixel values is encoded. 
     
     
       25. The method of claim 19, wherein the indicator specifies which type of the high dynamic range pixel values is encoded.