or green or mixed cyan. As outlined below, one may now, typically, use an image processing computer program to simulate the effect of using color filters, using as a source image a pair of either color or monochrome images. This is called mosaicking or image stitching. In the 1970s filmmaker Stephen Gibson filmed direct anaglyph blaxploitation and adult movies. His "Deep Vision" system replaced the original camera lens with two color-filtered lenses focused on the same film frame. In the 1980s, Gibson patented his mechanism. Many computer graphics programs provide the basic tools (typically layering and adjustments to individual color channels to filter colors) required to prepare anaglyphs from stereo pairs. In simple practice, the left eye image is filtered to remove blue & green. The right eye image is filtered to remove red. The two images are usually positioned in the compositing phase in close overlay registration (of the main subject). Plugins for some of these programs as well as programs dedicated to anaglyph preparation are available which automate the process and require the user to choose only a few basic settings. Stereo conversion (single 2D image to 3D) There also exist methods for making anaglyphs using only one image, a process called stereo conversion. In one, individual elements of a picture are horizontally offset in one layer by differing amounts with elements offset further having greater apparent changes in depth (either forward or back depending on whether the offset is to the left or right). This produces images that tend to look like elements are flat standees arranged at various distances from the viewer similar to cartoon images in a View-Master. A more sophisticated method involves use of a depth map (a false color image where color indicates distance, for example, a grayscale depth map could have lighter indicate an object closer to the viewer and darker indicate an object further away). As for preparing anaglyphs from stereo pairs, stand-alone software and plug-ins for some graphics apps exist which automate production of anaglyphs (and stereograms) from a single image or from an image and its corresponding depth map. As well as fully automatic methods of calculating depth maps (which may be more or less successful), depth maps can be drawn entirely by hand. Also developed are methods of producing depth maps from sparse or less accurate depth maps. A sparse depth map is a depth map consisting of