1. A density calculating apparatus comprising: an image data acquisition section that acquires print image data representing a print image to be printed by a printing system, the printing system setting print densities of color materials having a plurality of colors and printing an image based on the image data by using the color materials in the print densities; a place designating section that designates a place on the print image represented by the print image data acquired by the image data acquisition section; a target color acquisition section that acquires a target color of a color of the place; a color guess section that guesses a print color of the place to be printed by the printing system on the basis of a corresponding relationship between print densities and colors of patches, which patches are obtained by printing the chart image in each print density by the printing system based on the chart image data representing a chart image where patches having a plurality of colors line up while the print density of each of the color materials having the plurality of colors is changed to a series of print densities, as well as on the basis of a tentative print density that is designated for each of the color materials having the plurality of colors, the printing system producing the print color of the place based on the print image data and the tentative print density; and a density calculation section that calculates the print densities of the color materials having the plurality of colors by using the color guess section so that the target color acquired by the target color acquisition section is achieved at the place by the printing system based on the print image data.