Posterization

Posterize (of English posterization, . Posterized images) refers to the photographic effect of posterization (or tonality value ) with simultaneous Tonwertreduktion. The effect is used as a means of artistic design or as the first step in the tracing. A further description of the effect is the Greek Posterized, which relates to the resulting zones of the same brightness.

Creative application

First of three or more density separations of normal Halbtonnegativen are created by repeatedly copying to hard working lith material. This creates an image that implements the entire tonal range of the original recording in a few tones (for example, white, gray, black). In traditional photography, the copying is preferably hard-working lith film is used, which is exposed differently or developed long. The individual tones representing films are precisely mounted above each other and enlarged.

As with most photographic effects here also simplifies the effort for electronic image processing. In the photograph, manipulated in a standard image editing program, the levels were reduced to five, at the same time, the remaining partially inked after in the individual contrast was also withdrawn. Here, an image that is reminiscent of Pop Art is created.

Changed image

The picture shows the pond in the water lily house of the Royal Gardens of Kew in London. The inserted histograms illustrate what happens with the tonal values ​​in this effect.

Banding

The effect can also be undesirable artifact of the technical - created process - mostly digital. He is then called banding. Banding shown by the fact that a brightness curve is represented not uniform but in visible demarcated strip (English band).

Causes of banding with digital cameras are about:

• Unfavorable tone curves at camera sensor.
• Too low a brightness resolution in the processing chain - usually eight bits per color channel (JPEG ), ie 256 brightness values ​​. With high quality cameras therefore partly ten, twelve, or fourteen bits are used in order not to limit the dynamic range of the sensor that reaches, for example, 9.0.
• Subsequent image processing, such as lightening or contrast change.