A method and apparatus of depth of field rendering which simulates larger apertures for images captured at a smaller aperture. The depth of field rendering provides selective simulation of out-of-focus effects which are attainable with cameras having a larger aperture when capturing images at a smaller aperture. A blur function model is created based on the relationship between the blur change and the aperture change. This model is used to determine the blur difference which would arise between two images taken at two different apertures. Then the out-of-focus effect is generated by blurring the image in a rendering process based on the blur difference.