Method and computer program product for compressing and decompressing imagery data

Abstract

Techniques are provided for compressing and decompressing image data which may reduce the distortion that may otherwise be created by the compression of data values representative of null posts, overlays or other features that differ from the underlying image. In compression, a coefficient generated by a forward wavelet transform may be replaced with respective replacement coefficients. The transformed image data is then subjected to an inverse wavelet transform to generate modified image data in which the data values which differ from the underlying image have been replaced by interpolated or extrapolated values. The modified image data may be compressed in accordance with wavelet-based image compression. Alternatively, wavelet image compression may be applied directly to the coefficients resulting from the modified forward wavelet transform. In decompression, the compressed image data may be decompressed and data values representative of null posts or other features may be replaced with their original values.

That which is claimed is: 
     
         1 . A method of decompressing image data comprising a plurality of data values, the method comprising:
 identifying original data values for a first subset of data values;   decompressing a compressed representation of the image data in accordance with a wavelet-based decompression technique;   identifying respective locations of one or more data values of the first subset; and   replacing the one or more data values of the first subset with respective original data values.   
     
     
         2 . A method according to  claim 1  wherein identifying original data values for a first subset comprises providing a map of the original data values for the first subset as well as the respective locations of the original data values within the image data. 
     
     
         3 . A method according to  claim 2  wherein providing the map of the original data values comprises providing an encoded representation of the map and decoding the encoded representation of the map. 
     
     
         4 . A computer program product for decompressing image data comprising a plurality of data values, the computer program product comprising at least one computer-readable storage medium having computer-readable program code portions stored therein, the computer-readable program code portions comprising:
 a first executable portion for identifying original data values for a first subset of data values;   a second executable portion for decompressing a compressed representation of image data in accordance with a wavelet-based decompression technique;   a third executable portion for identifying respective locations of one or more data values of the first subset; and   a fourth executable portion for replacing the one or more data values of the first subset with respective original data values.   
     
     
         5 . A computer program product according to  claim 4  wherein the first executable portion includes instructions for providing a map of the original data values for the first subset as well as the respective locations of the original data values within the image data. 
     
     
         6 . A computer program product according to  claim 5  wherein the first executable portion includes instructions for decoding an encoded representation of the map.