We present an object-based fractal coding scheme based on the partitioned iterative function system (PIFS) that is similar to the standard fractal image coding schemes. The partitioned blocks in our object-based fractal coding scheme are classified as boundary blocks and internal blocks according to their shapes. The boundary blocks are located in the boundary region of an object and their shapes are arbitrary, whereas the internal blocks are located in the internal region of an object and their shapes are square. As the internal blocks do not affect the blocks to appear in the process of the ordinary fractal coding except that the domain pool is not an image but an object, encoding for the internal blocks follows the ordinary fractal coding schemes as they are. However, the boundary blocks should be carefully handled, as they have properties that make them different from the internal blocks, i.e., they have arbitrary shapes and their domain pool is composed of the internal blocks not the boundary blocks. Considering these properties, we propose three methods to encode the boundary blocks by making an alteration to the shapes of range blocks and domain blocks, and a method to encode them using the predecoded internal blocks. The methods are mathematically analyzed and their performance is experimentally evaluated. (C) 1999 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(99)01412-9].