Deep Image (Editing) - Heuristic42

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An image is the result of [rendering](/1/rendering/). The rendering process is often seen as the main part of the work. Historically, that may have been true --- getting the image is certainly the first stage, but once that job is done the result can be improved. *Post processing* is further work done after rendering. Images can be combined with other images or used as input in further rendering passes. For example, shadow mapping, deferred shading and a whole range of image space techniques such as depth of field, ambient occlusion and even further rendering called *image based rendering*.

Colour is still the desired end result, but for post processing and intermediate results more information can be very useful. For example, an image may store [material](/26/rendering/materials/) information or surface normals to be used in further lighting calculations.

Regular, flat images have one value per pixel. A *deep image* on the other hand is still a 2D grid of pixels, but each pixel, or *deep pixel*, can have multiple and varying numbers of values (possibly zero). This provides more complete information for further processing. This should not be confused with a [deep framebuffer](/21/opengl/framebuffer/), where all pixels have the same number of different attributes forming a *value*.

Color and depth form typical values in a deep image, providing a discretized geometry representation. With the original projection used to create the image the exact position of the surface samples are known. These surface samples have a direct relation to the concept of *fragments* from rasterization.

Deep images are increasingly being used in real-time graphics. The A-buffer has informally become a common term for GPU constructed deep images, and while there are similarities the original purpose was storing micro-polygons for antialiasing in the REYES system.

A deep image is significant in a rendering pipeline in that it provides a complete state where all fragments are available instead of processing and discarding them on the fly. Without this state, interactions between fragments are limited by one-at-a-time processing and, for rasterization, unknown rendering order. In particular for rasterization, complex "multi-fragment effects" such as transparency normally require geometry ordering and guaranteeing correct results for general cases is often impractically slow.

* This page is taken largely from [Real-Time Deep Image Rendering and Order Independent Transparency](/users/4/pknowles/#research).

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