FAST DOWNSCALED INVERSES FOR IMAGES COMPRESSED WITH M-CHANNEL LAPPED TRANSFORMS

Compressed images may be decompressed and displayed or printed using d ifferent devices at different resolutions, Full decompression and resc aling in space domain is a very expensive method, We studied downscale d inverses where the image Is decompressed partially, and a reduced in verse transform is used to recover the image. In this fashion, fewer t ransform coefficients are used and the synthesis process is simplified , We studied the design of fast inverses, for a given forward transfor m, General solutions are presented for M-channel finite impulse respon se (FIR) filterbanks, of which block and lapped transforms are a subse t, Designs of faster inverses are presented for popular block and lapp ed transforms.