1. A color separation apparatus comprising: a target value acquisition device which acquires target values of colors to be reproduced in a printer from continuous-tone image data when the printer creates binary image data showing shape and arrangement of dots constituting an image for each color material; a dot threshold data candidate selection device which acquires candidates of dot threshold data including information on a threshold for each the dots for converting the continuous-tone image data into binary image data for each color material; a print profile acquisition device which acquires a print profile showing correspondence between device signal values and color system values in the printer for each of the candidates of dot threshold data; and a color separation device which allows the printer to calculate candidates of the device signal values on the basis of the target values of colors acquired by the target value acquisition device and the print profile, and determines dot threshold data for reproducing colors corresponding to the target values on the basis of the candidates of dot threshold data and the print profile from among the candidates of dot threshold data, as well as determines device signal values for reproducing colors corresponding to the target values from among the candidates of device signal values.