PROBLEM TO BE SOLVED: To provide a bit depth decomposition and allocation device which performs bit depth conversion between a high bit depth image and a plurality of low bit depth images, a bit depth coupling restoration device, an image encoding device, an image decoding device and a program therefor.SOLUTION: A bit depth decomposition and allocation device 20 is configured to decompose bits of a high bit depth image signal into a plurality of kinds, allocate them for a plurality of low bit depth image signals and generate the low bit depth image signals. A bit depth coupling restoration device 80 is configured to decompose bits of the plurality of low bit depth image signals and restore a high bit depth image. An image encoding device 10a includes a function of the bit depth decomposition and allocation device 20 and a function of image encoding processing, and an image decoding device 50a includes a function of image decoding processing and a function of the bit depth coupling restoration device 80.
