1. An image generation apparatus comprising: a holding unit configured to hold object data which includes positional information of an object and first appearance information of the object, for each of a plurality of objects; a generation unit configured to generate a pseudo three-dimensional image, wherein the pseudo three-dimensional image is obtained on a screen which is placed in a world coordinate system when each of the plurality of objects is projected on the screen, wherein the object is placed in the world coordinate system in accordance with the positional information included in the object data for the object which is projected; a forward conversion unit configured to convert a color value of each pixel of the pseudo three-dimensional image into a perceptual value, by using the first appearance information included in the object data for the object which is projected on each pixel; and an inverse conversion unit configured to generate a second pseudo three-dimensional image after color conversion, by converting the perceptual value of each pixel of the pseudo three-dimensional image into a second color value using predetermined second appearance information which is commonly used for each pixel.