Line-based compression for digital image data

Abstract

A method of compressing digital image data is provided that includes selecting an entropy code for encoding a line of pixels in the digital image data, wherein the entropy code is selected from a plurality of variable length entropy codes, using spatial prediction to compute a pixel predictor and a pixel residual for a pixel in the line of pixels, and selectively encoding the pixel residual using one of the entropy code or run mode encoding.

1 . A method comprising:
 receiving reference frame data from storage;   decompressing the reference frame data by at least:
 selecting an entropy code for decoding; 
 computing a pixel predictor; and 
 selectively decoding a pixel residual based on the pixel predictor using the entropy code or using run mode decoding. 
   
     
     
         2 . The method of  claim 1 , wherein receiving the reference frame data comprises retrieving compressed data from the storage. 
     
     
         3 . The method of  claim 2 , further comprising reading an indicator of the entropy code from the compressed data,
 wherein selecting the entropy code is based on reading the indicator of the entropy code.   
     
     
         4 . The method of  claim 1 , wherein receiving the reference frame data comprises retrieving the reference frame data from off-chip memory. 
     
     
         5 . The method of  claim 4 ,
 wherein the reference frame data is first reference frame data,   wherein receiving the first reference frame data comprises retrieving compressed reference frame data from the off-chip memory, and   wherein the method further comprises, before retrieving the first reference frame data:
 compressing second reference frame data to generate the compressed reference frame data; and 
 storing the compressed reference frame data to the off-chip memory. 
   
     
     
         6 . The method of  claim 1 , wherein computing the pixel predictor comprises:
 computing a minimum absolute sample difference (MASD) for a current pixel based on neighboring pixels; and   computing the pixel predictor for the current pixel based on the MASD for the current pixel.   
     
     
         7 . The method of  claim 1 ,
 wherein selectively decoding the pixel residual comprises selectively decoding a first pixel residual of a current pixel, and   wherein the method further comprises:
 determining that a second pixel residual of a previous pixel equals zero; and 
 decoding the first pixel residual based on the pixel predictor using run mode decoding in response to determining that the second pixel residual equals zero. 
   
     
     
         8 . The method of  claim 1 , further comprising reconstructing a current pixel based on the pixel predictor and the pixel residual after decoding the pixel residual using the entropy code. 
     
     
         9 . The method of  claim 1 , further comprising:
 generating a picture based on the decompressed reference frame data; and   displaying the picture.   
     
     
         10 . A system comprising:
 a memory; and   one or more processors operable to:
 retrieve reference frame data from the memory; 
 decompress the reference frame data by at least:
 select an entropy code for decoding; 
 compute a pixel predictor; and 
 selectively decode a pixel residual based on the pixel predictor using the entropy code or using run mode decoding. 
 
   
     
     
         11 . The system of  claim 10 , wherein the reference frame data retrieved from the memory includes compressed data. 
     
     
         12 . The system of  claim 11 ,
 wherein the one or more processors are further operable to read an indicator of the entropy code from the compressed data, and   wherein the one or more processors are operable to select the entropy code based on reading the indicator of the entropy code.   
     
     
         13 . The system of  claim 10 , wherein the memory includes off-chip memory that is external to the one or more processors. 
     
     
         14 . The system of  claim 13 ,
 wherein the reference frame data is first reference frame data,   wherein to retrieve the first reference frame data, the one or more processors are operable to comprises retrieve compressed reference frame data from the off-chip memory, and   wherein the one or more processors are further operable to, before retrieving the first reference frame data:
 compress second reference frame data to generate the compressed reference frame data; and 
 store the compressed reference frame data to the off-chip memory. 
   
     
     
         15 . The system of  claim 10 , wherein to computing the pixel predictor, the one or more processors are operable to:
 compute a minimum absolute sample difference (MASD) for a current pixel based on neighboring pixels; and   compute the pixel predictor for the current pixel based on the MASD for the current pixel.   
     
     
         16 . The system of  claim 10 ,
 wherein to selectively decode the pixel residual, the one or more processors are operable to selectively decode a first pixel residual of a current pixel, and   wherein the one or more processors are further operable to:
 determine that a second pixel residual of a previous pixel equals zero; and 
 decode the first pixel residual based on the pixel predictor using run mode decoding in response to determining that the second pixel residual equals zero. 
   
     
     
         17 . The system of  claim 10 , wherein the one or more processors are further operable to reconstruct a current pixel based on the pixel predictor and the pixel residual after decoding the pixel residual using the entropy code. 
     
     
         18 . The system of  claim 10 ,
 wherein the one or more processors are operable to generate a picture based on the decompressed reference frame data, and   wherein the system further comprises a display configured to display the picture.   
     
     
         19 . A non-transitory computer-readable medium having executable instructions stored thereon, configured to be executable by one or more processors for causing the one or more processors to:
 compress first reference frame data to generate compressed reference frame data;   store the compressed reference frame data to off-chip storage;   retrieve the compressed reference frame data from the off-chip storage;   decompress the compressed reference frame data by at least:
 selecting an entropy code for decoding; 
 computing a pixel predictor; and 
 selectively decoding a pixel residual based on the pixel predictor using the entropy code or using run mode decoding. 
   
     
     
         20 . The non-transitory computer-readable medium of  claim 19 , wherein the instructions are executable by the one or more processors for further causing the one or more processors to:
 read an indicator of the entropy code from the compressed reference frame data, wherein the instructions to select the entropy code include instructions to select the entropy code based on the indicator;   generate a picture based on the decompressed reference frame data; and   display the picture.