1. An image coding device comprising: image disassembling means for disassembling an input multivalued image into at least one pair of sub-images in a continuous data stream and generating disassembled images composed of the at least one pair of sub-images in the continuous data stream, at least one sub-image of the at least one pair of sub-images having a bit depth greater than one; image referring means for referring to peripheral pixels of coded other disassembled images with respect to objective pixels of the disassembled images generated by said image disassembling means; probability estimating means for estimating a probability estimated value corresponding to a probability that the values of the objective pixels are produced by the reference of said image referring means; and coding means for coding the disassembled images produced by said image disassembling means using the probability estimated value estimated by said probability estimating means.