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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.

379 news items

 
Bloomberg
Thu, 30 Oct 2014 13:52:28 -0700

Maybe President Barack Obama should have stuck with basketball. During an interview with Ahmad Rashad, NBA legend Michael Jordan gave Obama a verbal posterization. Asked to name his dream foursome for a round of golf, Jordan picked Arnold ...

SB Nation

SB Nation
Thu, 30 Oct 2014 05:05:28 -0700

James Ennis might not be a household name, but a lot more people are sure to know him now after this posterization of Rasual Butler. Poor Butler might have to think about retirement after that one.

Bleacher Report

Bleacher Report
Wed, 29 Oct 2014 22:32:30 -0700

They were rapt during a six-minute "Heat Nation" short film, narrated by Alonzo Mourning, and with James only fleetingly making an appearance, as a Cavalier, in the camera shot of Dwyane Wade's memorable posterization of Anderson Varejao. And they ...
 
All U Can Heat
Wed, 29 Oct 2014 19:01:15 -0700

I predicted that James Ennis would have four Holy Crap Highlights this season. I may have undersold him. James Ennis absolutely annihilated Rasual Butler on a posterization dunk that sent AmericanAirlines Arena on fire. This is the promise of Ennis ...

TSN

TSN
Sun, 26 Oct 2014 10:58:17 -0700

Ross's season was highlighted by a filthy posterization of Kenneth Faried and then equaling the Raptors' record for points in a season with 51 in a January game against the Clippers. Though it seemed that Ross struggled with confidence in the playoffs, ...
 
PC Magazine
Fri, 17 Oct 2014 11:00:00 -0700

I also observed posterization—sudden shifts in color where they should be gradual—in some scenes. Related Story See How We Test Projectors. Audio from the 1-watt speaker is feeble. To hear it, you'll want to either sit very near the projector or ...
 
PC Magazine
Wed, 15 Oct 2014 07:48:45 -0700

The projector handled shadow detail (details based on shading in dark areas) well, and I saw barely a hint of posterization (shading changing suddenly where it should change gradually) in clips that tend to cause that problem. Colors are nicely ...

Air Alamo

Air Alamo
Fri, 10 Oct 2014 06:15:48 -0700

David has put together some highlights for you ranging from Cory Joseph's posterization of Serge Ibaka to some beautiful highlights of the Spurs system being executed to perfection. Check them out here! Our next piece we have for you is also from ...
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