1. A method of adjusting a rendering sampling rate of an image, comprising: providing an initial sampling rate; determining a regional variation value representing regional data, color, and/or alpha variation; determining an accumulated opacity value representing opacity accumulated over a ray in the image; determining a regional opacity value representing regional opacity; accessing a quality setting representing a default sampling rate; and adjusting the sampling rate as a function of the regional variation value, the accumulated opacity value, the regional opacity value, and the quality setting.