The invention relates generally to a method of and an arrangement for copying a colored original.
More particularly, the invention relates to a method of and an arrangement for determining the amount of light required in each of the three primary colors during the copying of a colored original.
In color copying, the so-called neutral gray correction may be used to eliminate color tinges or casts due to the nature of the material, e.g., paper or exposed and developed film, constituting the original to be copied. The neutral gray correction is performed by using a photoelectric measuring device to regulate the exposure of the original in each of the three primary colors. The amounts of light in the primary colors are selected in such a manner that the copy is a neutral gray on average.
When the subject matter of the original has so-called color dominants, that is, intensively colored areas, use of the neutral gray correction during automatic exposure control results in poor copies. The reason is that the neutral gray correction then leads to color falsification in the copies.
Accordingly, the neutral gray correction should not be employed when color dominants are present. This raises the problem of distinguishing between color tinges and color dominants.
The German Auslegeschrift No. 25 35 034 discloses a photographic color copying apparatus having a photoelectrically controlled exposure control unit. Different regions of the original are scanned individually to determine the color compositions thereof and relationships between the three primary colors are established for each of the regions. When a clear color imbalance exists in one or more regions, special procedures are employed to eliminate the color dominants from the calculations which are used to determine the neutral gray correction factor. One such procedure involves using only measurements from regions having a proper color balance in the determination of the neutral gray correction factor.
When large regions of an original have a color imbalance, the preceding procedure exhibits the disadvantage that the neutral gray correction factor, and hence the exposures in the different colors, are based upon a relatively small proportion of the original.