[pure-silver] Re: The Quest
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Thu, 14 Dec 2006 14:21:04 -0800
----- Original Message -----
From: "Bill Stephenson" <photographica@xxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Thursday, December 14, 2006 2:05 PM
Subject: [pure-silver] Re: The Quest
OK, I give up! I had never heard the term "unsharp mask"
until I ventured (slightly) into the digital world. (And,
until today, had only heard it applied to digital.) How
does one accomplish "unsharping" in the analog film realm?
Thanks for the enlightenment,
-Bill
The unsharp mask is an old technique in analogue
photography. First of all a "normal" mask is a device used
to reduce the contrast of an image. Most often it is a light
negative made from a color transparency and layed over it in
intimate contact during printing. Color transparencies tend
to be high in contrast because they are made for direct
viewing. By adding a light negative mask a sort of automatic
burning and dodging is done to lower the contrast.
An unsharp mask is similar except that it is made unsharp
by spacing it away from the transparency. this is often done
by simply putting the mask back to back with the
transparency rather than with the emulsions touching. The
spacing is just enough to make the mask slightly blury. The
mask still lowers overall contrast but, because the fine
details are blurred, it does not lower the contrast of them.
The result is an exageration of the contrast of fine details
including edges. This is interpreted by the eye as in
increase in sharpness.
Of course, a positive mask can be used for getting the
effect when the original is a negative rather than a
transparency.
A simple method of producing a mask is to contact print
the original (negative or positive). The mask is developed
to rather low contrast and overall density. The exact value
must be determined by experiment. Straight contrast making
is pretty commonly done when making reversal prints on
materials like Ilfochrome from color transparencies.
Masking can also refer to the use of similar low contrast
masks in color printing to correct for spurious color
response of the original material. The object here is,
however, different from simple contrast masking but the term
should be understood in order not to confuse the two.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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