Already in the mid-1980s, System Brunner first carried out extensive tests to determine how human color perception reacts to color variations in different types of pictures. A wide variety of persons was included in the tests.
A picture always 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 any variations. One can also say contrasts instead of variations. 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 balance shifts in the mid-tone area. Changes to the color balance in printing arise mainly through diverging variations in the tone value increases of the three process colors CMY and the so-called gray balance. Other influencing metrics such as changes of picture gradation (lightness differences, tonality) or overall contrast (saturation, gamut) 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.
With low-contrast pictures on the other hand, the human eye reacts more sensitively to color variations and therefore the tolerance limit for color variations is much lower before the acceptance question arises.
For this reason, today used colorimetry with Delta E*ab used today is obsolete as a gauge for perceived color differences in the images because only the individual isolated colors are compared to one another. Delta E*ab is process blind and picture pertinent.
The findings of picture analysis by "Picture Contrast Technology" were later taken into account in the color control technology Instrument Flight®
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 technology helps printing companies to show customers that visible differences between the proof and the production run, or within the production run, are picture-related and cannot be used as a basis for a general judgment of quality.
Homogeneous areas of three superimposed colors (CMY) which cannot be reproduced by the offset process without visible deviations. Variations in the mid tone color balance of +/- 1% are already noticeable. The tolerance limit lies within the center of the HEXAGON
Low-contrast pictures, predominantly gray and brown tones, also skin tone reproductions 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
Medium- to strong-contrast pictures, which covers a majority of image reproductions. 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
Pictures with very strong color contrasts. The question of acceptance arises with color balance deviations of +/- 6% and more in the mid-tone area. The tolerance limit lies within the third ring of the HEXAGON
Due to printing process variations, class 0 and 1 pictures can only be printed with medium to strong GCR (Gray Component Replacement) to avoid visible color variations.
© System Brunner AG, CH-6600 Locarno