From: brad@optilink.UUCP (Brad Yearwood)
Newsgroups: rec.arts.movies
Subject: Re: Technicolor (was: REVIEW: THE LAST OF THE MOHICANS) (long)
Keywords: author=Oswalt
Date: 1 Oct 92 02:54:20 GMT
Organization: Optilink Corporation, Petaluma, CA

In article <1992Sep29.164724.25384@cs.ucla.edu>, reiher@ficus.cs.ucla.edu (Peter Reiher) writes:
> In article <1992Sep29.134220.10432@cbnewsj.cb.att.com> sun!megatest!jao (John Oswalt) writes:
> ...
> In processing the film, the three negatives were combined into a single
> print, with special dyes applied based on the relative exposure of each
> of the three strips.  Since each strip encoded color information for a
> different color, it was possible to (sort of) recreate the original color
> of the scene.  In actuality, the process was not able to capture certain
> colors very well, and heightened other colors.  On the whole, the result
> was much more brilliant and beautiful color than one typically finds
> in today's films.  (Note that I have probably made some minor mistakes
> in the details of the process.  I can never remember whether the three
> negatives were combined into a single color negative, for instance, or
> whether a color positive was produced from the three black-and-white
> negatives.  I'm sure someone will be kind enough to correct any mistakes
> I've made.)

I believe there was an earlier 2-strip Technicolor process which was in fact
incapable of representing considerable chunks of color space.

3-strip Technicolor is no more "sort of" than the integral tripack color film
that most of us are familiar with.  Actually, the in-camera separation process
is better in principle, because the separation filters can be made with
cleaner band cuts (less crossover) than you get from the combination of
different sensitizing dyes per-layer and some built-in subtractive filtering
in integral tripack.  I'm going to venture a guess that a panchromatic
monochrome film also has a more linear exposure/density response than do
the narrower-band-sensitized layers in integral tripack.

Technicolor's imbibition print process was a continuous strip version of
the dye transfer process which is still used today for top-grade ($$$)
photographic prints.  Dye transfer prints are made from a special thick-emulsion
positive film called a "matrix".  In principle, the camera negative could be
printed directly to matrix (positive), which is then dye-transfer (imbibition)
printed to the final print film.  In practice, there might have been another
two negative-process steps or one reversal step so the camera negative would
not have to be handled more than once, or a very few times (a matrix has a
finite lifetime, so if you want to make a large number of prints, you need
to make more than one set of matrices).

Take a dark area in the original scene.  To make a dark area in the final
print, we want to deposit a lot of dye in that area.  The camera negative
is transparent where the original scene is dark.  Printing the camera negative
to matrix film exposes the matrix most where the negative is transparent -
where the original scene was dark.  The special developer used for matrix
film hardens the gelatin emulsion more in areas which receive more exposure.
A carefully controlled wash in hot water removes gelatin more quickly from
the matrix in areas which received less exposure.  You end up with thicker
gelatin in areas where the original scene was dark, and little/no gelatin in
areas where the original scene was bright.

The matrix film (after drying and other steps) is sent through a dye bath.
It absorbs dye in proportion to gelatin thickness.  The print is made by
pressing the matrix film against a gelatin-coated final print film.  The
final print film is prepared in a way (acid/base balance, mordant salts)
which causes it to attract and retain dye from the matrix film.  The process
is repeated in succession for 3 matrices, with yellow, magenta, and cyan dyes.

Each print step must be in perfect registration relative to the other steps,
and this registration must be held for a considerable amount of time to
allow the dye to transfer.  This is difficult enough with a simple still
picture, and even more challenging with a long slithery strip of wet film
kept in motion through a continuous process.  I believe Technicolor printers
used long serpentines of stainless steel bands with registration pins to hold
the films during transfer.

> ... 
> Most significant, perhaps, was the fact that you needed a camera large 
> enough to contain three separate strips of film, the optics necessary 
> to split and filter the light beam, and the mechanism to keep the three 
> strips in synchronization.  Technicolor cameras were large and heavy, 
> compared to normal cameras.  One can suppose that, had they kept working 
> at it, methods would have been found to make them somewhat lighter and 
> more portable, but the fact that you need three of almost everything that 
> a normal camera needs one of is pretty much inescapable. ...

One key thing that you need at least 3 times as much of is light.  Consider
that the light was being passed through half-silvered beam splitter mirrors
and absorption filters for color separation.  Maybe we could do a bit better
today with dichroic mirrors (as some color TV cameras used), but you're still
dividing the light by more (splitter and filter losses) than the nominal 3
negatives' worth.

> ...
> Also, assuming one saves the original three black-and-white negatives, 
> and assuming they don't fall apart, one can always restore the color to 
> its original state by going back to them and redoing the entire process.  
> (That's in principle, I believe, as I think there are no longer any 
> facilities in the U.S. capable of making a Technicolor print from the
> negatives.)  So Technicolor is superior for film preservation purposes.
> On the other hand, saving three black-and-white negatives takes up as
> much room in your temperature and moisture controlled archive vault as 
> storing one color negative.

There are quite likely no Technicolor dye imbibition printers left anywhere
in the world.  I believe I remember reading that the last one in the U.S. was
sold to China some years ago.  There's no need to redo the process per se, as
you should be able to print the separation negatives in 3 passes (through
respective color filters) onto modern integral tripack print film.

Last time I looked (around 10 years ago), Kodak made monochrome films
specifically intended for doing archival separations from integral tripack
color negative, so printing from separations is likely to be available from
at least some movie labs.

It would be interesting to determine how much of the wonderful appearance of
3-strip Technicolor was due to in-camera separations, how much was due to
Technicolor's tight control over the photography (including lighting and set
and costume colors), and how much was due to the imbibition printing process.

I believe that dye transfer, particularly from in-camera separations,
carries a longer tonal range to the final print.  This is particularly
evident in scenes where a given color is taken through a dark-to-bright
range.  One example would be a piece of satin cloth with folds and direct
lighting, so you get everything from shadow to near-specular highlights.
Also on things like polished automobile finishes.  One particular example
from an old book on color photography was a silver bowl of fruit.  Something
about the highlights on the fruit and a realism in the silver that you just
don't see from integral tripack color film (however much it has improved over
the years).

Brad Yearwood   brad@optilink.com    {uunet, pyramid}!optilink!brad
Petaluma, CA