Hardware implementation of a color image decoder for remote database access

Database client hardware and associated algorithms that can be used to call a remote database server using commercial ISDN lines for retrieval of image information are described. Compressed images are stored in the server and transferred over the ISDN channel at 64 kb/s. This information is reconstructed at the client using a single 50-MHz AT&T WE DSP32C signal processor and auxiliary display hardware. Compression is accomplished using a 4 by 4 subband filterbank and a perceptual error measure operating in the subband domain. The perceptual measure determines what information can be discarded, with the rest quantized using differential pulse code modulation (DPCM), Huffman encoded and stored at the server. When retrieved, the client performs the inverse operations. A color image of 512 by 480 pixels can be compressed to 0.7 b/pixel, transferred to the client in 3 s, and reconstructed in 6 s, with results nearly indistinguishable from the original