According to an embodiment of the invention, a high-speed and high-image-quality image decoding method and apparatus for a compressed signal including plural components or a block code in which different compression systems are combined. In an image decoding method in which compressed data of an image signal including plural components including a resolution component expressed by the n-th power of 2 (where n is an integer equal to or greater than 0) and processed by a frequency conversion system is decoded by inverse frequency conversion of each component, a resolution component of each compressed data for each component is individually set and decoded when decoding resolution at the time of decoding is lower than the highest resolution of the compressed data.