2D to 3D Video Conversion is a process of transformation that is applied to the original video stream in its decompressed form in order to create a video stream that has apparent depth to it when viewed using one of the existing 3D video playback technologies.
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Several techniques of 2D to 3D video conversion are known to produce varying degrees of satisfactory 3D picture.[1][2][3][4][5]
Perhaps the most straightforward technique for 2D to 3D conversion, depth mapping requires significant manual effort to implement accurate depth and protrusion. The idea is that a separate auxiliary picture known as the "depth map" is created for each frame or for a series of homogenous frames to indicate depths of objects present in the scene. The depth map is a separate grayscale image having the same dimensions as the original flat image, with various shades of gray to indicate the depth of every part of the frame. While depth mapping can produce a fairly potent illusion of 3D objects in the video, it inherently does not support semi-transparent objects or areas, nor does it allow making use of occlusion. The technique has at one point been introduced to the consumer market use as part of the 2D-plus-depth coding implemented by Philips, but was subsequently discontinued.[6]
A development on depth mapping, multi-layering works around the limitations of depth mapping by introducing several layers of grayscale depth masks to implement limited semi-transparency. Similar to a simple technique,[7] multi-layering involves applying a depth map to more than one "slice" of the flat image, resulting in a much better approximation of depth and protrusion. The more layers are processed separately per frame, the higher the quality of 3D illusion tends to be.
The technique known as anaglyph image transposition is based on a visual illusion which human brain perceives as genuine three-dimensional image. If the same image is transposed on top of itself with a small horizontal offset (a couple percent at most) with red and cyan color filters applied to each image, the resulting picture will appear three-dimensional to human eye. Remarkably, transposition produces a 3D effect comparable in depth to more sophisticated techniques that require two distinct pictures taken from different angles to be overlaid on top of each other. Whereas depth mapping and multi layering requires a certain degree of manual processing to perform, anaglyph image transposition is simple and crude enough that it can be fully automated.
It is only with recent advances in computer technology that has become possible to apply this kind of transformation to a series of frames in a motion picture reasonably fast so that 2D to 3D video conversion software could be created to fully automate anaglyph transposition. Several implementations exist that rely on this technique to convert regular 2D video to 3D for viewing with red-cyan glasses on a TV or computer screen. Similar to most video transcoding applications, 2D to 3D video conversion software can most commonly deal with various input formats. The typical processing algorithm will include demuxing the video stream out of the video file, decompressing it if necessary, then transforming the picture to anaglyph 3D to subsequently compress and mux back the video and any other source streams into the output video file. It is also worth noting that modern high-performance computers are capable of applying anaglyph transposition to a video stream on-the-fly in real time, so it is also a technical possibility to play back 2D video in pseudo 3D (such as stereoscopic anaglyph) without pre-converting it.