An image processing apparatus which makes it possible to correct the image density of a target color in real time and maintain highly accurate image density characteristics over a long term. In a first control, the output of a laser driver is controlled such that the gradation of an image signal coincides with that of an image to be recorded on a sheet. The density level of a developed patch to be formed on a photosensitive drum is set to a different value on a toner color-by-toner color basis. In a second control, the output from the laser driver is controlled such that the density of the developed patch coincides with a reference density. An LUT generated in the first control is corrected according to the difference between the density of the developed patch and the reference density.