NetNews Usenet Archive 1992 #27/NN_1992_27.iso/spool/rec/photo/20384

Internet Message Format | 1992-11-23 | 7.0 KB

Path: sparky!uunet!charon.amdahl.com!amdahl!JUTS!RUTS.ccc.amdahl.com!bjs
From: [e-mail] (Barry Sherman)
Newsgroups: rec.photo
Subject: Re: Contrast mask woes
Message-ID: <[e-mail]>
Date: 23 Nov 92 21:51:06 GMT
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Reply-To: [e-mail] (Barry Sherman)
Organization: Amdahl Corporation, Sunnyvale CA
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Michael C. Adler writes:

>I tried to make a contrast mask this weekend for a 35mm transparency and
>now have a question.  The scene was essentially a black and white image
>(though taken on Kodachrome) of a deep black volcanic peak with patches
>of snow as well as very puffy clouds behind it.  There is about a 5 stop
>difference between the detail in the clouds and the detail in the mountain
>and the actual detail within each object covers about 1 stop in each range.
>Your basic printing nightmare.
>
>It just so happens that dodging would work perfectly well for this image
>since the two separate exposure areas are rather easily separated but I
>wanted to try using a contrast mask to find out what the effect would be.
>
>I made a mask that seemed about the minimum density to make the image
>printable without dodging.  I wouldn't say the cloud region was especially
>dark.  The mask had relatively low but perceptible detail (developed about
>1/3 of normal) and was unsharp.  When I laid the mask over the slide a miracle
>occurred:  the subtle detail in the clouds disappeared completely.  The mask
>compensated perfectly for the original and generated a very nice gray.
>
>I don't believe using an intermediate highlight mask would have worked since
>the detail was too subtle.  I'm also not convinced that I can make a mask
>with much less contrast (perhaps I'm wrong).

Ya know, there are two ways to go about highlight masking.  One, the
intermediate highlight mask and the other a highlight "bump" mask.  I'm
almost an expert on the subject since I just got back today from a 3 day
workshop on masking for Ciba printing.  :-)  I already understood the
basics but the instructor had lots of nifty ideas that made it well
worth while.

I suspect that the highlight mask could work - it's just a matter of making
it strong enough.  I'm assuming here that you're referring to working in
register and making a negative mask with density only in the highlight
areas to be sandwiched with the original when making the contrast reduction
mask, thereby reducing contrast *in the contrast reduction mask*, preventing
contrast reduction in the highlight areas in the final print.

If that's a safe assumption then you could make a stronger mask.  Either
expose it longer, develop it longer or both.  It might take a little
experimentation.  What I found *really* useful about this workshop was
the way that the instructor used potassium ferricyanide (Farmers Reducer)
to tweak highlight masks.  He made one which was as dense as he wanted
in the highlight (enough so that the highlight would not show detail in
the final contrast reduction mask) but that left lots of other stuff
showing in the highlight mask which should not have been flattened in
the contrast reduction mask.  Then he just poured a little potassium
ferricyanide in a beaker, added some water and painted it on the
areas of the highlight mask that should have been clear.  When he dipped
it in some fixer the silver just vanished, leaving him with a strong
highlight mask, but only in the areas where it was desired!  Sometimes
he had to paint and dip a few times to get the effect that he wanted, but
it worked well.

The other type of a highlight mask is called a "bump" mask.  This is made
with a reversal litho film named Kodak LPD4.  When developed in D11 it
produces a mask which is all black except for the highlight areas.  In use,
one makes a base exposure with the original and the contrast reduction
mask.  Then one, in the dark, removes the contrast reduction mask and
places the bump mask on top of the original.  One can then make a very
localized "burn" exposure on only the highlights, restoring contrast within
those areas.  Alternatively, of course, one can use regular Kodalith and
contact print the first exposure onto another sheet to get one which is
all black except for the highlights.

All of this assumes the ability to work in register.

It sounds to me as if a strong intermediate highlight mask might be the
easiest way to go, rather than trying to find an exposure which would
differentiate the 1 stop difference in densities in the highlights.  It might
be that after making the base exposure with the contrast reduction mask
you would find that the clouds had detail but had been reduced in value
too much.  In that case it'd be easy to make a bump mask which was clear
over all of the cloud area and make the bump exposure to raise the value of
the clouds.

>Any suggestions on what I could do differently?

Not really, other than the above.  The instructor strongly recommended using
Pan Masking film since it is designed to give unsharp masks.  He said that his
tests indicated that it's not a low-contrast film as is often said.  He found
that its contrast is about that of Tmax 100.  He recommended developing in
HC110 diluted 1:11 from stock for 2 inutes for a 20% mask, 3 minutes for a 30%
mask ...  Exposure to be determined by the individual for his/her own
equipment.

For intermediate highlight masks he recommended using Kodalith Ortho film
developed in dilute D11 (I forget the dilution).  For highlight bump masks
he recommended Kodak LPD4 developed in straight D11.

He also mentioned what he called a "super mask" in which he made an
intermediate highlight mask and then contacted it onto another sheet of
Kodalith, developed in dilute D11. The result, when sandwiched with the
original and used to make a contrast reduction mask, permitted *increasing*
highlight contrast while lowering highlight values, resulting in increased
highlight contrast with lower over-all contrast.

Lotsa fun stuff that you can do with masking.   'Course digital imaging
techniques will make it all obsolete in a few years.  Guess I'll  have to find
a new hobby then.  :-)

Barry
--


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| Barry Sherman, Amdahl Corp.  | PROGRAM: n. A magic spell cast over a com-  |
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