The present disclosure provides a method and device for image coding and a method and device for image decoding, and the method includes: a representative pixel set of a coding block is constructed, and information for constructing the representative pixel set is determined; predicted values of pixel samples in the coding block are constructed, a generation manner for the predicted values including: constructing the predicted values of the pixel samples according to reconstructed pixel samples in an image region outside the coding block and pixel values of the representative pixel set; and the information for constructing the representative pixel set and information for constructing the predicted values are coded and written into a video bitstream.