American Cinematographer - December 1960 - 35

There are several traveling matte processes, the
one to be employed being selected for reasons of
economy or personal safety for achieving an effect
impossible to achieve in a conventional way, or for a
combination of these requirements.
In the conventional rear-screen process a back¬
ground called the plate is projected onto a screen,
the foreground action is put in front of the screen,
the two elements are photographed, and a composite
negative with the two elements combined is recorded.
Obviously the portion of the background which is
eclipsed by the foreground is not photographed. It
stands to reason, therefore, that if this portion of the
background could somehow be left unexposed when
making the plate, the foreground could then be ex¬
posed onto that unexposed area or '■'hole." This is
exactly the principle of all traveling matte processes.

FIG. 2-Curves graphically explain core of process. Solid line is sensi¬
tivity curve of infrared film. Broken line is transmission curve of dichroic
filter coating on foreground lighting equipment used in process.

Infrared Traveling Matte Process

The infrared traveling matte process was invented
and patented by Leonard Pickley and developed to
its present efficiency by MPO Videotronics, Inc.,
through many months of experimentation and re¬
search.
The beamsplitter camera used by MPO is the
3-Strip Technicolor camera, developed for the Tech¬
nicolor process. It uses three strips of film: two in
one gate and one in the other. We have modified this
camera to the extent that we use only two strips of
film and have changed the beamsplitter prism to suit
our purpose. We thread the gate behind the prism
with a film stock sensitive to visual light, such as all
panchromatic films or color films, and from now on
we shall call these films "visual films." We then
thread the so-called bi-pack side of the camera with
infrared film, which is sensitive to the infrared por¬
tion of the spectrum from about 700 to 900 ms. The
infrared part of the spectrum covers a much larger
range, but we are concerned only with that portion to
which our infrared film stock is sensitive.
The problem was to expose the background and
nothing but the background on the infrared film. At
the same time we wanted to expose the foreground
action and nothing but the foreground action on the

visual film. Obviously, if we could achieve that, then
we could simply make a print of the infrared nega¬
tive which we call a matte-bi-pack this matte when
we print the plate, and print the foreground action
into the resulting hole. This is exactly what the vari¬
ous traveling matte processes are doing in one man¬
ner or another.
Preparation of Background

In order to achieve our purpose we had to be
able to "light" the background with infrared rays.
(This is a paradox because infrared rays are invisi¬
ble to the eye and therefore it is incorrect to call
them "light" in our terminology.) At the same time
this background had to appear black to the visual
film. Therefore we had to find a black background
which was only infrared reflective.
After some research we found a black velour
which, when treated with a certain black dye (name
and formula unknown, but the material is available
through theatrical drapery supplies), is quite infra¬
red reflective. Further, we found that by backing up
Continued on Page 756

-H

B
I(\L _ _ ^
1

D
FIG. 3-How the infrared self-matting process works: Subject in foreground is lit with minusinfrared illumination while background is "illuminated" with minus-infrared rays. Beam-splitter in
camera at left separates and diverts the +IR and -!R images to their respective negatives.

DECEMBER

* 1960

FIG. 4-C and D show how infrared is reflected
by specially coated glass (or prism), as com¬
pared with examples A and B.

741

American Cinematographer - December 1960

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