An image forming system includes a pseudo-halftoning device; an image forming apparatus that forms a toner image on a recording medium; and a reading apparatus that read the toner image on the recording medium, in which the pseudo-halftoning device is such that pseudo-halftoning is performed on a target image by using a threshold matrix set including a plurality of threshold matrices, one threshold matrix for use is selected from the threshold matrix set according to a position of the target image to be used in the pseudo-halftoning performed on the target image, the threshold matrices in the threshold matrix set are identical with one another in periodic structure but different from one another only in a gradation characteristic, and a threshold matrix to be used is determined based on toner-image information data obtained by reading the toner image by the reading apparatus.