TROBIC: two-row buffer image compression

We describe a color image compression and decompression scheme suitable for high resolution printers. The proposed scheme requires only two image rows in memory at any time, and hence is suitable for low-cost, high-resolution printing systems. The compression ratio can be specified and is achieved exactly. Compound document images consisting of continuous-tone, natural regions mixed with synthetic graphics or text are handled with uniformly high quality. While the target compression ratios are moderate, the quality requirements are extremely high: the compressed and decompressed printed image needs to be virtually indistinguishable from the original printed image. The scheme combines a lossless block coding technique with a wavelet block codec. The wavelet block codec uses a new and simple entropy coding technique that is more suitable for the specific block-structure, compression target, and discrete wavelet transform used.