The Posterization or posterization of an image requires continuous tone gradation conversion to multiple regions with fewer tones, with sudden changes from one tone to another. This was initially done with the photography process to create a poster. It can now be done photographically or by digitally processing images, and may be deliberate or unintentional artifacts of color quantization.
Video Posterization
Cause
The effect can be made intentionally, or happens by accident. For artistic effects, most image editing programs provide posterization features, or a photographic process can be used.
Unwanted posterization, also known as milkfish, can occur when the color depth, sometimes called bit depth, is insufficient to accurately take on a continuous tone gradation. As a result, continuous gradients appear as a series of discrete steps or color bands - hence the name. When discussing the appearance of fixed pixels, such as LCD and plasma televisions, this effect is called a false contour. In addition, compression in image formats such as JPEG can also generate posterization when the fine gradient of color or luminosity is compressed into discrete quantized blocks with a flattened gradient. The result can be further compounded by optical illusions, called the illusion of Mach bands, where each band seems to have a gradient of intensity in the direction of opposing the overall gradient. This problem can be solved, in part, by dithering.
Maps Posterization
Photography process
Posterization is a process in photo development that converts normal photos into images consisting of different areas, but different flat, tone or color. A poster image often has the same general appearance, but the part of the original image presented transitions gradually replaced by a sudden change in shadows and gradations from one tone area to another. Printing the posterization of black and white requires the separation of density, which is then printed on the same sheet of paper to create the whole image. Separation can be done by density or color, using different exposures. Part Density can be created by printing three prints of the same image, each at different lighting times to be combined for the final image.
Apps
Typically, posters are used to track contour lines and realistic photo vectorization. This tracking process starts with 1 bit per channel and progresses to 4 bits per channel. Because the bit per channel increases, the number of color brightness levels may increase.
A visual artist, faced with a line art that has been corrupted through JPEG compression, may consider posterizing the image as the first step to remove the artifact on the edge of the image.
Posterize time
Temporal temporalization is the visual effect of reducing the number of video frames, while not reducing the speed at which it actually plays. This is compared with ordinary posterization, where the number of individual color variations decreases, while the overall color range is not. The effect of the movement is similar to the flashing flashing effect, but without the contrast of light and dark. Unlike pulldown, unused frames are simply discarded, and are intended to be clear (longer than the persistence of vision that video and motion pictures usually depend on). Animated GIFs often look like posters because their frame rates are usually low.
More formally, this is downsampling in the time dimension, as it reduces the resolution (the accuracy of input ), not the bit rate (output precision , as in the posterization).
The resulting stop-go movement is the temporal form of jaggies; formally, aliasing form. This effect may be intent, but to reduce the frame rate without introducing this effect, one can use temporary anti-aliasing, which results in blur.
Compare that with the stretch time, which add the frame.
See also
- Downsampling
- Quantization error
- Discretion error
- Quantization of colors
References
- Langford, Michael. The Darkroom Handbook . New York: Dorling Kindersley Limited, 1981. 245-249.
- Jasc Software. Paint Shop Pro Help , 1998.
Note
External links
- https://web.archive.org/web/20060106051841/http://desktoppub.about.com/cs/graphicstips/f/posterization.htm
- https://web.archive.org/web/20060202015057/http://www.sphoto.com/techinfo/wdtech.html
Source of the article : Wikipedia
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