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Example of a photograph in JPEG format (24-bit color or 16.7 million colors) before posterization, contrasting the result of saving to GIF format (256 colors). Posterization occurs across the image, but is most obvious in areas of subtle variation in tone.
Posterized photo of a hibiscus.

Posterization of an image entails conversion of a continuous gradation of tone to several regions of fewer tones, with abrupt changes from one tone to another. This was originally done with photographic processes to create posters. It can now be done photographically or with digital image processing, and may be deliberate or may be an unintended artifact of color quantization.

Cause[edit]

The effect may be created deliberately, or happen accidentally. For artistic effect, most image editing programs provide a posterization feature, or photographic processes may be used.

Unwanted posterization, also known as banding, may occur when the color depth, sometimes called bit depth, is insufficient to accurately sample a continuous gradation of color tone. As a result, a continuous gradient appears as a series of discrete steps or bands of color — hence the name. When discussing fixed pixel displays, such as LCD and plasma televisions, this effect is referred to as false contouring.[1] The result may be compounded further by an optical illusion, called the Mach band illusion, in which each band appears to have an intensity gradient in the direction opposing the overall gradient. This problem may be resolved, in part, with dithering.

Photographic process[edit]

Posterization is a process in photograph development which converts normal photographs into an image consisting of distinct, but flat, areas of different tones or colors. A posterized image often has the same general appearance, but portions of the original image that presented gradual transitions are replaced by abrupt changes in shading and gradation from one area of tone to another. Printing posterization from black and white requires density separations, which one then prints on the same piece of paper to create the whole image. Separations may be made by density or color, using different exposures. Density Separations may be created by printing three prints of the same picture, each at a different exposure time that will be combined for the final image.

Applications[edit]

Typically, posterization is used for tracing contour lines and vectorizing photo-realistic images. This tracing process starts with 1 bit per channel and advances to 4 bits per channel. As the bits per channel increases, the number of levels of lightness a color can display increases.

A visual artist, faced with line art that has been damaged through JPEG compression, may consider posterizing the image as a first step to remove artifacts on the edges of the image.

Posterizing time [edit]

Temporal posterization is the visual effect of reducing the number of frames of video, while not reducing the speed at which it actually plays. This compares to regular posterization, where the number of individual color variations is reduced, while the overall range of colors is not. The motion effect is similar to the effect of a flashing strobe light, but without the contrast of bright and dark. Unlike a pulldown, the unused frames are simply discarded, and it is intended to be apparent (longer than the persistence of vision that video and motion pictures normally depend on). An animated GIF often looks posterized because of its normally-low frame rate.

More formally, this is downsampling in the time dimension, as it is reducing the resolution (precision of the input), not the bit rate (precision of the output, as in posterization).

The resulting stop-go motion is a temporal form of jaggies; formally, a form of aliasing. This effect may be the intention, but to reduce the frame rate without introducing this effect, one may use temporal anti-aliasing, which yields motion blur.

Compare with time stretching, which adds frames.

See also[edit]

References[edit]

  1. ^ "HDTV World Glossary". CNET Networks. 2007. Retrieved 2007-06-06. 

External links and sources[edit]

  • Source: Langford, Michael. The Darkroom Handbook. New York: Dorling Kindersley Limited, 1981. 245-249.
  • Source: Jasc Software. Paint Shop Pro Help, 1998.

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Posterization — Please support Wikipedia.
This page uses Creative Commons Licensed content from Wikipedia. A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia.
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1353 news items

USA TODAY High School Sports

USA TODAY High School Sports
Sun, 21 Dec 2014 19:14:00 -0800

While Jones' slam was definitely good enough to win (though to be fair, he did clip Simmons in the head), it was no less spectacular than his posterization of 6-7 Sierra Canyon (Chatsworth, Calif.) forward Cody Riley on Friday in an a game at the City ...

Dime Magazine

Dime Magazine
Sun, 21 Dec 2014 10:45:00 -0800

College hoops may not see a better posterization all season long – and almost certainly won't involving a dunker and victim with such a massive height discrepancy. (Video via ACC Digital Network). What do you think? Follow Dime on Twitter at @DimeMag.
 
NBCSports.com
Fri, 07 Nov 2014 19:00:33 -0800

Purdue steamrolled NAIA opponent Carroll College (Montana), 90-49, on Friday night in the final exhibition game for the Boilermakers. The highlight of the evening was Jon Octeus' driving by one opponent with an in-and-out move before throwing down a ...
 
NetsDaily
Sun, 07 Dec 2014 09:18:13 -0800

With little more than a minute left, Brown drove in from the right, blowing by Kent Bazemore and neatly hitting Jefferson with a pocket pass that he converted into perhaps the most impressive dunk by any Net this season, a one-handed posterization of ...

Yahoo Sports (blog)

Yahoo Sports (blog)
Mon, 01 Dec 2014 22:35:31 -0800

If Belinelli were ever to dunk on someone, it would not register as a posterization, because the use of the term suggests that any manufacturer would create a poster of a player doing something he almost never does. I mean, Chris Paul has blocked 60 ...
 
PC Magazine
Mon, 08 Dec 2014 10:11:15 -0800

I saw some minor issues, but only in the most demanding test clips, which we use precisely because each one tends to bring out a specific problem. Among these is a hint of posterization (shading changing suddenly where it should change gradually) in ...
 
NBCSports.com
Sat, 06 Dec 2014 19:29:56 -0800

... some players will call a timeout in that spot others will attempt to throw the ball off of the defender, which is what Iverson attempted to do here. Unfortunately for Bradley's Mike Shaw, the ball wound up in King's hands. The result: an impressive ...

HDTV Test

HDTV Test
Tue, 16 Dec 2014 06:32:40 -0800

The actual calibration process itself remained laborious (not helped by us having to exit the menu to cross-check against greyscale and colour ramps from time to time), but we didn't observe any significant increase in posterization in both test ...
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