An image coding device for coding block data each including a plurality of pixels by selecting, for each block data, one of a lossy mode and a lossless mode in which coding includes use of a dictionary with different colors each registered in a corresponding one of p (p is a natural number) dictionary indexes, the image coding device including: an irreversible coding unit configured to perform coding in the lossy mode in a case where the number of unregistered colors is greater than a reference value, q (q is a number identical to the p) colors most recently coded in the lossless mode in a case where the number of unregistered colors is less than or equal to the reference value.
Image coding device, image coding method, and image coding system