Re: Photo Filtration

de Derald 01/19/2007 07:13

Richard Steinfeld <rgsteinYOHOHO@Asonicdotnet.net> wrote:

>Kodak used to make filters for fluorescents, the FLD and FLB, for
>daylight- or tungsten-balanced films, respectively. These worked quite
>nicely for most purpuses, and of course, like all other filters, were
>manufactured by other companies as well. Kodak also used the reverse of
>these compensations to fix color prints in their photo labs. I'd like the
>equivalent of these filters, only within an image-editing program
>
>If this is solvable, we can use this method for cheap lighting for
>general indoor digital photography.

For many years, I used a 16-bit freeware program that did exactly
what you want. It was calibrated in Kodak Wratten density values. If I
can find it, I'll certainly let you know. However, I believe it was a
Kodak product so you may find it at Kodak's WWW site. You'll find an
excellent Photoshop plugin here:
http://www.mediachance.com/ (dce tools) but it is not free. Note: Many
freeware image editors support Photoshop plugins. Mediachance seems to
have removed most of its (excellent) free tools from distribution; at
least, I couldn't find them. You also may find this useful, although, I
cannot vouch for it: http://www.opanda.com/en/pf/
I might suggest, though, that you're working from the wrong end.
Since you're doing tabletop/studio work where you have control, I
suggest that you balance the light source to the "film" using the same
kind of filtering gels that cinematographers (for example) use.
Unfortunately, digital cameras' spectral respones do not mimic those of
film so you'll have to experiment and those gels are expensive and
short-lived. You may be able to get them for little-or-nothing from a
(motion picture) grip or lighting services company, if there are any in
your area. Those gels fade so quickly that, for professional purposes,
they are essentially single-use items (I've worked for DPs and LDs who
change them out after about an hour's time) but they are fine for
individual private studio use where they won't be subjected to sunlight,
carbon arc lights, xenon, etc.
Nowadays, I do a lo-o-ot of tabletop digital photography using a
(two, actually) Kodak Z740 (which was preceded by a Kodak DC-50) and
have minimized color balance problems through the use of off-camera
photo-strobe "bounce" flash (I *knew* there was some reason to keep
those old softlight umbrellas). It is a simple-enough matter to use one
of those optical "slave" flash triggers and the on-camera light to
operate your studio light(s). Just be sure to mask the on-camera light
completely from the subject or you'll get unexpected highlights and/or
shadows. I have rather a large gamut of photostrobes, ranging from tiny
"inky dinky" to full-fledged high power studio strobes to provide a wide
range of background lighting effects, highlighting, etc. and only the
primary light is cabled to the camera.
Correction is well within Irfanview's capabilies. Practical
advanges are that color cast is minimal and, most importantly, uniform
within the same setup so that after calibrating a test exposure I can
use I'view's batch processor to "automagically" apply the correction as
the images are transferred from the camera. One of I'view's weaknesses,
though, is that (as far as I can determine) correction values are not
picked up from the test image, making it necessary to explicitly enter
them manually.
--
HTH,
Derald