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Statistically, images have more low-frequency than high-frequency content, so it is the low-frequency content that remains after quantization, which results in blurry, low-resolution blocks. In the most extreme case only the DC-coefficient, that is the coefficient which represents the average color of a block, is retained, and the transform ...
The images are in many cases chosen to represent natural or typical images that a class of processing techniques would need to deal with. Other test images are chosen because they present a range of challenges to image reconstruction algorithms, such as the reproduction of fine detail and textures, sharp transitions and edges, and uniform regions.
A precursor to the SMPTE test pattern was conceived by Norbert D. Larky (1927–2018) [5] [6] and David D. Holmes (1926–2006) [7] [8] of RCA Laboratories and first published in RCA Licensee Bulletin LB-819 on February 7, 1951. U.S. patent 2,742,525 Color Test Pattern Generator (now expired) was awarded on April 17, 1956, to Larky and Holmes. [9]
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Earlier RGBW filter pattern. Another 2007 U.S. patent filing, by Edward T. Chang, claims a sensor where "the color filter has a pattern comprising 2×2 blocks of pixels composed of one red, one blue, one green and one transparent pixel," in a configuration intended to include infrared sensitivity for higher overall sensitivity. [9]
In a raster scan, an image is subdivided into a sequence of (usually horizontal) strips known as "scan lines".Each scan line can be transmitted in the form of an analog signal as it is read from the video source, as in television systems, or can be further divided into discrete pixels for processing in a computer system.
A number of compatible shapes that extend pattern blocks are commercially available. Two sets of "Fractional Pattern Blocks" exist: both with two blocks. [7] The first has a pink double hexagon and a black chevron equivalent to four triangles. The second has a brown half-trapezoid and a pink half-triangle.
Dither is an intentionally applied form of noise used to randomize quantization error, preventing large-scale patterns such as color banding in images. Dither is routinely used in processing of both digital audio and video data, and is often one of the last stages of mastering audio to a CD .