Image generation apparatus, image generation method, image generation program, and integrated circuit for rendering a target pixel in a target scene by using Z-buffering

An image generation apparatus that renders a target pixel in a target scene by using Z-buffering, comprising: a unit that calculates a statistical value indicating distribution characteristics of Z depth values in a predetermined scene; a unit that, by using the statistical value, converts a Z depth value for the target pixel into a converted Z depth value; a unit that generates a first Z depth value for the target pixel by using the converted Z depth value and generates a second Z depth value for the target pixel by using the converted Z depth value or the Z depth value for the target pixel; and a unit that performs a first comparison using the first Z depth value as one comparison subject and, only when the first comparison cannot be successfully performed, performs a second comparison using the second Z depth value as one comparison subject.