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Re: "Dye-transfer process"



At 12:49 AM 7/3/97 -0700, you wrote:
>Hi guys,
>Could anybody enlighten us on exactly how the "dye-transfer" process
>really works? Howcome this process was 'put on the shelf' for so many
>years? Looking forward to your replies
>
>Regards,
>Mark.....
>
I have had some experiences with IB or "Dye Transfer" processes over the
years, and I'll attempt to give you a quick summery.

Before Eastman Color Negative became reality, the only particle way to
produce full color was by exposing 3 black and white negatives at the same
time in what is known as a Technicolor camera. Each strip of film or "color
record",  was exposed using separation filters, and then processed to a
specific gamma at the lab. It won't amaze you that the blue record is the
weakest  and grainiest of the three, and therefore requires special
handling in processing. (sound familiar?). The films were very slow, about
25 ASA, so 300 footcandles (or more) were required on the set in order to
set a reasonable f-stop on the camera.

To produce a full color print, each of the separation negatives is
contacted printed to a very special type of silver based black and white
positive film. Developed in a Tanning Developer and fixed using no
hardener, the result is a positive gelatin relief type image (somewhat like
a photo gravure plate) with "nooks and crannies". Each strip of film or
matrices is then dyed using the complimentary sub primary color. The layer
of gelatin on each matrices absorbs an amount of dye in proportion to the
exposure in density, and is then placed in contact with a clear dye
receptive estar support base coated with gelatin.

The dye "transfers" across to the support base, and after a quick buffering
bath, it is now ready for the steps to be repeated for the remaining two
colors. The real technology here is the mechanical process for keeping each
of the three color records in complete and total registration with the
images already transferred to the base material while traveling a fairly
high speeds. An added complication is that each matrices must remain in
contact with the support base for sufficient time to allow all of the dye
to make the transition.

The result is a color print produced using no traditional photographic
chemicals, and containing only very stable organic dyes. Technicolor prints
have a very long life span of up to 50 years and more, and are not subject
to the effects of chemical fading that plagues the multi layered
photographic prints in use today. And what do they look like? You will gasp
when you see real Three Stripe Technicolor projected side by side with more
traditional prints. The blacks are much cleaner and darker with no loss of
detail, and yet the contrast index does not suffer as a result.  Because of
the control of using three black and white separations, the color can be
controlled much closer and tighter, and even the contrast can be reasonably
altered. The result is a print unlike anything seen today with much purer
colors. The reds are bold and saturated with out turning orange, the blues
are deep and vibrant, and the green does not get into everything else. It
is possible to have a correct skin tone AND true neutral gray in the same
scene.

With the advent of Eastman Color negative stock, the original three strip
camera and the black and white separations were scrapped in favor of
exposing the matrices directly from OCN. Although an Interpositive will
still be produced as a backup, the Technicolor process does not require
either the Interpositive or the  Internegative to produce release prints.
It also eliminates the printing steps in between. Yes, it's true:  the
Technicolor Release print becomes only 1 generation away from the original
negative instead of the traditional 4.

Why did Technicolor stop production? I suppose it was thought that 50 year
technology was being replaced by something faster and cheaper and less
complicated, but that same "modern" technology is now allowing Technicolor
to update the IB process to the point that some day soon, it might just be
faster and cheaper than the more traditional photographic based chemical
process.

Kodak used to publish a very informative book on Dye Transfer. Perhaps a
trip to the library might just be in order for anyone desiring additional
information.

Tom Nottingham
Complete Post Telecine

PS - A call to Manns Chinese Theatre could not confirm that indeed the
Technicolor IB print was presented on the dates published. Box Office
personel indicated that the information in the trades was incorrect.

+++
Thanks to Colorlab of Maryland for support of the TIG in 1997
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