Downscaled inverses for M-channel lapped transforms

Compressed images may be decompressed for devices using different resolutions. Full decompression and rescaling in the space domain is a very expensive method. We studied downscaled inverses where the image is decompressed partially and a reduced inverse transform is used to recover the image. We studied the design of fast inverses, for a given forward transform. General solutions are presented for M-channel FIR filter banks of which block and lapped transforms are a subset.