Provided is an image processing device which has: an image input part configured to input a multi-spectral image which includes N (N is an integer of 4 or more) channels corresponding to N bands; a reference vector setting part configured to cause a user to set, as three reference vectors, three types of N-dimensional vectors having sensitivities of the respective N bands as elements; and a conversion part configured to convert the multi-spectral image into a 3-channel image including three channels by decomposing a spectral distribution of each pixel of the multi-spectral image on the basis of the three reference vectors.