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Posterization in a black and white photo

Posterization (from English posterization ; posterized images ) describes the photographic effect of tone separation (or tone value separation) with simultaneous tone value reduction. The effect is used as a means of artistic creation or as a first step in vectorization . Another name for the effect is the Greek Isohelie , which refers to the resulting zones of equal brightness .

Design application

First, three or more density separations are created from normal halftone negatives by repeated copying onto hard- working lith material . The result is an image that converts the entire tonal range of the original recording into a few tonal values ​​(e.g. white, gray, black). In conventional photography, hard-working lith film is preferably used when copying , which is exposed or developed for different lengths of time. The films representing the individual tonal values ​​are precisely mounted on top of each other and enlarged. From Agfa there was a special film for this purpose, the AGFA Contour Professional , as the sheet film was offered and significantly simplified the procedure.

As with most photographic effects, the effort involved in electronic image processing is also simplified here . In the image on the right (see below), manipulated in a standard image processing program, the tone values ​​were reduced to five, at the same time the remaining ones were partially colored after the contrast had also been reduced for some of them . This creates an image that is reminiscent of Pop Art .

The picture shows the pond in the Water Lilies House in Kew Gardens in London. The displayed histograms illustrate what happens to the tonal values ​​in this effect.


The effect can also arise as an undesirable artifact of the technical - mostly digital - process. It is then called banding . Banding is the fact that a brightness profile is not uniform, but in visible delimited strips (engl. Tape is shown).

Some of the causes of banding in digital cameras are:

  • Unfavorable tone value curves with the camera sensor .
  • Too low a brightness resolution in the processing chain - eight bits per color channel ( JPEG ) are common, i.e. 256 brightness values. In high-quality cameras, ten, twelve or fourteen bits are sometimes used in order not to limit the dynamic range of the sensor, which reaches 9.0, for example.
  • Subsequent image processing such as brightening or changing the contrast.

Web links

Commons : Posterization  - collection of images, videos and audio files

Individual evidence

  1. ^ Günther Schwarz: AGFA contour film OCLC 4523401