Nikon LS-3500 - LS-3510 - Manual (Page 67)

Scanning for Reproduction 7-3
Software Reference for Scanners
For all E-6 or similar process slide films such as Agfachrome, Ektachrome,
Fujichrome, etc., (the “chrome” stands for color coupler names such as
mydochrome and tolochrome) the couplers are incorporated in the manufactured
film.
The K-14 Kodachrome process is rather special in that it starts out as a
monochrome film with no color couplers and they are added when the film is
processed. This process is a very difficult to control, but it has remained a favorite
among 35mm photographers for some time. Color negative (C-41 process) films
also employ couplers and are engineered to be more accurate in color reproduction
by using special “mask” couplers to make up for the deficiencies in the cyan,
magenta, and yellow dye transmission characteristics. The reason for these
deficiencies is similar to what is discussed in the ink-based printing process in the
Undercolor Removal procedure.
All dyes and pigments are to some extent deficient in their color spectral
transmission. This means that they do not transmit the ideal bands of light that we
are interested in. For example, magenta dye formed from couplers transmits a little
too much yellow (or rather absorbs too much blue), making it appear too red.
In transparency films, there is not much we can do to alleviate the problem
except to improve the dye balance and structure. In negative films, since we
anticipate going to a CMY based photo printing paper that is exposed with
tungsten light, we can add masks to the dye layers to compensate for the
deficiency in the original image color characteristics. The same technique applies
to the cyan layer. In general, color negative films tend to scan with better results
than transparencies, because they have a flatter gamma (lower contrast) and the
Dmax is relatively low. Also, the mask colors help to improve color reproduction,
the grain size has been diminished for the relative film speed, and the emulsions
are considerably sharper than they used to be. For the photographer, these films
have much more latitude, that is they tolerate much greater over and under
exposure while retaining detail (flat gamma helps).
Offset printers have shunned these films in the past because they are much
harder to separate on traditional drum scanners. Sharpness usually suffered when a
printer had to scan a positive print or transparency made from a second generation
dupe of the negative original. Since the reading routines on the Nikon scanner
have been tailored to match both positive and negative emulsions, this is no longer
a constraint.
When images are printed with ink, we must use the same subtractive
primaries to form the image as in the photographic printing process. These process
colors consist of Yellow, Magenta, Cyan, and blacK inks formed from finely
ground pigments much the same way watercolor dyes are made, except that the
pigments for dyes are much more finely ground and are usually in aqueous, or
water-based mixtures. Printers inks are mostly oil-based and use carbon-based
solvents.
In the offset lithography process, the master plate consists of a two-
dimensional or non-relief image. The printing dots are formed by exposing a
gelatin coated plate to ultraviolet light. The areas that are so exposed are