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A 1-bit image of the Statue of David, dithered with Floyd–Steinberg algorithm. Floyd–Steinberg dithering is an image dithering algorithm first published in 1976 by Robert W. Floyd and Louis Steinberg.
The simplest application of image geometry correction is a specific case known as keystone distortion correction derived from Keystone effect.Keystone distortion gets its name from the symmetric trapezoidal distortion resulting from misaligned projector placement in the vertical dimension (although the term is generally applied to the non-symmetric quadrilateral shape that occurs from an off ...
If the difference is greater than a user-specified threshold setting, the images are (in effect) subtracted. Digital unsharp masking is a flexible and powerful way to increase sharpness, especially in scanned images. Unfortunately, it may create unwanted conspicuous edge effects or increase image noise.
In geometric optics, distortion is a deviation from rectilinear projection; a projection in which straight lines in a scene remain straight in an image.It is a form of optical aberration that may be distinguished from other aberrations such as spherical aberration, coma, chromatic aberration, field curvature, and astigmatism in a sense that these impact the image sharpness without changing an ...
The term dither was published in books on analog computation and hydraulically controlled guns shortly after World War II. [1] [2] [nb 1] Though he did not use the term dither, the concept of dithering to reduce quantization patterns was first applied by Lawrence G. Roberts [4] in his 1961 MIT master's thesis [5] and 1962 article. [6]
The edge direction angle is rounded to one of four angles representing vertical, horizontal, and the two diagonals (0°, 45°, 90°, and 135°). An edge direction falling in each color region will be set to a specific angle value, for instance, θ in [0°, 22.5°] or [157.5°, 180°] maps to 0°.
For artistic effect, vignetting is sometimes applied to an otherwise un-vignetted photograph and can be achieved by burning the outer edges of the photograph (with film stock) or using digital imaging techniques, such as masking darkened edges. The Lens Correction filter in Photoshop can also achieve the same effect.
The effect is especially noticeable the closer the camera is to the subject, as its amount increases the shorter the focal length is at the same field size. One notable director that frequently employs rectilinear ultra wide angle lenses in order to achieve a distinctive signature style defined by extreme perspective distortion is Terry Gilliam .