[rollei_list] Re: OT: B&W Filters in digital...Pola filters
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Mon, 12 Jul 2010 18:16:19 -0700
----- Original Message -----
From: "CarlosMFreaza" <cmfreaza@xxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Monday, July 12, 2010 6:04 PM
Subject: [rollei_list] Re: OT: B&W Filters in digital...Pola
filters
2010/7/12 Laurence Cuffe <cuffe@xxxxxxx>:
What about a Pola-Screen? I can not find a
reference to polarization in the IB for my camera.
Marc
Yes good point. Thats another glaring exception to the
notion that it can
all be done in Photoshop.
Regarding a polarizing filter for PS and others image
edition
software, it's necessary to distinguish two main practical
effects you
can obtain from a regular true polarizing filter used
during the image
taking. The effect to obtain deeper and darker blues for
the sky and
for the greens, etc. can be obtained using PS or similar
software
judging the image after to take it, you don't need a
Pola-Screen for
this case. It can be done working with the R-G-B channels
in PS or it
can be easily done with simpler tools like the Sky
graduated filter
from Picasa. This is a method for PS:
http://photoshoptutorials.ws/photoshop-tutorials/photo-effects/polarizing-filter.html
However there is another very useful effect you can obtain
from a true
Pola filter (Rolleipol f.e.) that cannot be obtained from
PS and
similars; this is the effect to eliminate reflections from
bright and
transparent surfaces allowing to capture subjects beyond
this surface,
f.e you wan to capture fishes and stones within clean and
transparent
water but the reflections are avoiding to see them,
turning the
Polafilter you'll find a point where the light is
polarized and the
reflections are eliminated allowing to capture fishes and
stones. If
you want to capture the _real_ image for this and similar
cases, you
need to use the filter during the image taking, PS cannot
invent the
real subject.
Carlos
---
There _is_ a difference between the effect of a color
filter and a polarizing filter on skys. The polarizer
darkens skys selectively because the blue light coming from
certain directions is polarized. The filter will have little
or no effect on other areas of similar color. While one
could duplicate the effect in an image editor it would have
to be done by selecting areas to change rather than applying
a filter effect to the entire image.
I also tend to agree with Eric that there is a
difference between post-detector filtering and manipulation
of the image. The colors of the image are already being
filtered effectively by the color spitter, whatever it is,
in the camera. It may be pretty broad. One has only the
output of the camea to manipulate. Filters can be more
selective than this meaning that when a filter is used on
the camera the variations in gray scale presentation of
particular colors may be different than can be gotten by any
manipulation of the generated image. This is also true of
color film where the selection of colors is done by the
filters built into the film and by the effective filtration
of the sensitizing dyes in the various emulsions. While a
monochrome image can be obtained from the original color
image and camera filters will have much the same effect as
on the camera, the effect can not be quite identical. This
may be an insignificant difference but it still should be
taken into account because it is important in understanding
the nature of the image once encoded in digital or by a
film.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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