In computer graphics

Computer graphics

Computer graphics are graphics created using computers and, more generally, the representation and manipulation of image data by a computer with help from specialized software and hardware....

, image order algorithms iterate over the pixel

Pixel

In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....

s in the image to be produced, rather than the elements in the scene to be rendered

Rendering (computer graphics)

Rendering is the process of generating an image from a model , by means of computer programs. A scene file contains objects in a strictly defined language or data structure; it would contain geometry, viewpoint, texture, lighting, and shading information as a description of the virtual scene...

. Object order algorithms are those that iterate over the elements in the scene to be rendered, rather than the pixels in the image to be produced. For typical rendering applications, the scene contains many fewer elements (for example, geometric primitive) than the image pixels. In those cases, object order algorithms are usually most efficient. But when the scene complexity exceeds that of the image, such as is the case often in volume rendering

Volume rendering

In scientific visualization and computer graphics, volume rendering is a set of techniques used to display a 2D projection of a 3D discretely sampled data set.A typical 3D data set is a group of 2D slice images acquired by aCT, MRI, or MicroCT scanner....

, then image order algorithms (for example, shear warp) will usually be more efficient.