The Salt Lake herald. [volume] (Salt Lake City [Utah]) 1870-1909, 1900-04-17

ing else. Every spectrum color there
Iore. IS simple. In its effect in the
eye, however, it may not be simple:
tldt Is, the color sensation may be due
70 the simultaneous action upon two
OF even three sets of the nerves in. the
retina, which are supposed 10 give rise
70 color perception. Moreover of two
nghts which produce the same color
eHeet, one may be simple-consistin of
one wave length only-and the other a
1uiilpouhd OF TWO or more wave lengths.
Inc eye does not analyze. and il is
PoSSIDle TO produce any color sensation
Whatever by combining in proper .pro-
portions three simple colors-red. green
ana violet. The relation which these
Urinary color sensations bear to one
aliother IN the normal eve is shown in
; ele cut me proportion in which each
MUST De excited to produce the effect
OF a given color is found bv taking the
heisht OF each curve above the hori-
<otitaI line at the point corresponding
20 the given color. and the action of
an at ence gives the effect of white.
Inc addition Of color in this way is
very different from the mixture of
paints, and the three primary colors
which are used in any process will DIFF
Ter according to the process.
Color Screens.
Suppose now that the light from any
source, bright landscape for instance
is passed through a plate Of clear ruby
glass. The ruby glass absorbs all col
ors except pure red, and the effect
OF using such a screen is therefore fo
sift out everything but red. one of the
primaries. photograph taken through
a RED screen will give plate in which
the form is reproduced in red values
and in no others
similar photographs taken without
moving the camera-merely changing
the screen for one of green or of violet
give other plates in which the picture
IS recorded in green or in violet values
The images will be similar in the three
plates and similarly placed, but Will
differ IN tone in the different parts in
accordance with the proportion of the
simple components which make I'D the
light of those parts.
Now, if pOsitives are made from the
three negatives and each color screen
combined with the positive correspond
lng-or the positives might be colored
with suitable red, green and violet dyes
we nave the elements of a color pho
tograph. The three colored positiyes
may be mounted in three lanterns and
white light projected through them.
When the three primary images are in
exact register on the screen of the
stereopticon the picture appears in its
natural colors.
This is the substance of the three
color process, whatever it's particular
notifications may be. If the three pos
itives are intended to be mounted to-
gether and viewed by transmitted light
then dyes of different colors must be
| used; for the action is one of subtrac-
ton instead of addition. We must be
sure that all the red gets through from
the red positive, all the green from the
green positive and all the violet from
the violet positive, and this is just
what would happen if the same colOrs
were used in the viewing screens that
were used in the taking screens.
The Jolly Process.
There is one modification Of the
three process as outlined above
in which the three primary plates are
combined in one. This is accomplished
in the following way: A screen is ruled
with fine lines. 200 or 300 or more to
the inch, the ruling being in the colors
chosen as primaries-in this case, or
ange, yellow-green and blue-violet.
The lines are colored in regular rota-
ton, the first orange, the second yell
low-green, the third blue-violet, the
fourth orange again, and so on. The
three primary color screens of the or
binary three-color process are thus, in
sense, combined in one. A single ex-
posture is made in the usual way
through this line screen and positive
obtained, giving the three component
color tones separately, but divided into
small portions in accordance with the
ruling. A second screen OF ruling ex-
actly similar to that Of the first is
placed in contact with the positive, and
the picture viewed by transmitted light
appears in its natural colors. The col
ors in the viewing screen are red, green
and blue-violet
The success Of this method depends
upon still another action in the eye it.
self. If the lines on any Of the plates
are seen very near to or under mag
MITIGATION they appear quite distinct and
separate. At some distance, however,
the sense of distinct form is lost, the
lines blend together and the mixture of
colors is accomplished by mixture Of
sensation in the eye.
1t is this same action that is RESPONSE
BILE for the color effects Of woven fab
ricS, the tone effects of engravings.
wood cuts and half-tOnes, and to some
extent the color effects in oil paintings.
The power of the eye TO distinguish
form is limited, and portions Of the
image upon the retina which lie very
close together are not seen as separate
images. Thus the black lines and white
spaces of line engraving when viewed
from a distance blend together and
produce the effect of a gray of greater
or less depth, according to the proper
tions of black and white.
Evidently the viewing screen in the
Jolly process to produce true colors
must be exactly in register with the
positive. each red viewing line exactly
above the line taken through the or
auge of the taking screen, and so on. If
it is shifted along by the width Of one
line a bright red becomes d brilliant