The Raytracing algorithm operates by following each ray of light striking the view plane backward through the model to its source. If a ray comes from light reflecting off an object's surface, the texture applied to that object helps determine what that reflected light should look like. That may include surface maps, reflectivity, shininess, or many other lighting factors. If the ray of light is coming from another object that is reflecting in the first object's surface, then the ray must be followed further backward from this surface to determine whether it came from another surface or from a light source.
This backward tracing continues until each light ray is accounted for, ending at either a light source or passing out of the scene. The minimum number of rays that must be traced is equal to the number of pixels in the image being rendered. The larger the image and the higher its resolution, the longer the rendering time. A 288 dpi image, for example, has four times as many rays to trace as a 72 dpi image of the same dimensions.