PURPOSE: To restore picture data of plural color components with one block as the unit by extracting code data related to the lightness, the structure, and the color of each block from received code data and restoring respective code data.

CONSTITUTION: An inputted RGB signal is temporarily stored in a 4-line buffer 301 and is read out in the 4×4 size to segment blocks. An L*a*b* transforming unit 302 transforms the signal from the RGB system to the L*a*b* system based on a prescribed transformation formula. Blocks of L* are orthogonally transformed by an orthogonal transformation part 304 to output a lightness signal L and a structure signal S through quantizers 307 and 309. Blocks of a* and b* are averaged in average circuits 311 and 312, and they are collectively quantized to color information C by a quantizer 313. A multiplexer 315 collects signals L, S, and C into one code to output an efficiently compressed encoded code. This encoded picture data is decoded to restore picture data of plural color components with one block as the unit.