Picture Contrast Technology
A picture consists of more than one color tone. When the eye sees more than one color tone at the same time, it is automatically influenced and confused by the difference. One can also say contrasts instead of differences. Contrasts determine the perception of color shifts in a picture, and every picture contains contrasts, e.g.

Color contrasts, light/dark contrasts, formal contrasts, simultaneous contrasts

Picture analysis by "Picture Contrast Technology" demonstrates how the human eye perceives color deviations in different types of pictures and shows that variations in the printing process and in reproduction are first visible as color balanceshifts in the mid-tone area. Changes to the color balance in printing arise through diverging deviations in the tone value increases of the three process colors CMY. Other influencing variables such as picture gradation (lightness) or overall contrast (saturation) are less noticeable.

The more pronounced the contrasts are, in a picture, the less sensitively the human eye reacts to color variations, and so the tolerances for color variations can be wider before the acceptance question arises.

In low-contrast pictures on the other hand, the eye reacts more sensitively to color variations and therefore the tolerances for color deviations are much narrower before the acceptance question arises.

For this reason colorimetry with Delta E*ab is obsolete as a gauge for perceived color differences in illustration printing. Colorimetry is process blind and not picture pertinent.

System Brunner Picture Contrast Classes
Practical people know from experience that some pictures are much easier to match and print than others. System Brunner was the first to quantitatively examine picture contrasts and classify pictures into contrast classes.

Picture contrast theory helps printing companies to show customers that visible differences between the proof and the production run are picture-related and cannot be used as a basis for a general judgment of quality.

System Brunner Picture Contrast Classes

Class 0
Homogeneous areas of three superimposed colors (CMY) which cannot be reproduced by the offset process without visible deviations. The tolerance limit lies within the center of the hexagon.

Class 1
Low-contrast pictures, predominantly gray and brown tones, also skin tones in a large area.
The question of acceptance arises with color balance deviations of +/- 2% in the mid-tone area.
The tolerance limit lies within the first ring of the hexagon.

Class 2
Medium to strong-contrast pictures which covers most originals / pictures.
The question of acceptance arises with color balance deviations of +/- 4% in the mid-tone area.
The tolerance limit lies within the second ring of the hexagon.

Class 3
Pictures with very strong color contrasts.
The question of acceptance arises with color balance deviations of +/- 6% and more.
The tolerance limit lies within the third ring of the hexagon.