skuggmaskmetoden - a new technique to regulate the contrast in photographic copying

摘要

To be able to control the contrast in photographic copying, especially for colour, it is desirable to let the whole of the original's tone spectrum be used whilst not overstepping the copy material's full tone spectrum.Contrast regulation has so far been carried out using three different techniques, either in combination or on their own:1. copying via an intermediary original2. copying through a half transparent mask, which is adapted in contact with the original3. prior illumination of the copy material with white light.Contrast control with the help of the shadow mask method occurs via:- exposure of the copying material is divided up into two or more steps,- each exposure step involves a definite part of the original's scale of tone which can then be controlled for suitable lighting on the copy- those parts of the original scale of tone which are not included in a defined exposure step are shaded by a photographically produced mask which is totally opaque in those parts of the original's scale of tone and transparent in the other parts.- the mask is produced via exposure of a defined area in the light path of an optical copying arrangement (enlargement unit), is developed and put back in the exact same spot.- the mask represents a picture of non-definition in this part of the light path.- the mask's placement in the light path decides how fine details in the original are broken up by the mask's shadow.