From: jerrelloyd (jerrelloyd_at_antispamdomain.not)
Date: Wed Nov 26 2003 - 12:48:07 EST
Just for fun, why don't you go to Photoshop, select Filter, Other,
Minimum, set it on one and see what happens.
Jerre
--- In digital_astro_.at._yahoogroups.com, <gregharp_.at._s...> wrote:
> I'm processing some shots of the Veil Nebula from last night, but
I'm having
> some trouble. Basically, while I can bring the levels up to the
point where
> I can see the nebulosity, I can't do so without bringing up so many
stars
> that it's like viewing it through a snow storm. I'm using
ImagesPlus but I
> also have Photoshop CS available, and I'm open to any other tools
that can
> help as well.
>
> Here's the relevant data:
>
> Canon 10D DSLR with 70-200mm f/2.8L lens set for 200mm and f/2.8,
ISO 1600,
> 30 individual exposures of 60 seconds, no filter (dark skies!
woohoo!),
> ambient temperature 32F (0C). The images were converted from raw
to 16-bit
> TIFF and calibrated with a dark frame averaged from twelve
originals shot
> shortly after the light frames were taken, a flat frame averaged
from five
> originals shot at twilight metered to produce a medium tone (as an
> experiment to compare results to shooting a gray card), and a bias
frame
> averaged from five shots at ISO 100 and 1/4000. They were then
translated
> and rotated (the latter necessary because I did a poor job of
aligning the
> mount) in ImagesPlus.
>
> I've tried stacking these multiple different ways, but I get pretty
much the
> same results at different levels. I've done min/max excluded
average on all
> 30 frames, I've done adaptive addition of all 30, and I've done
simple
> addition on six sets of five frames (producing, effectively, six
five minute
> exposures) and then min/max excluded averaged those six images.
The only
> processing I've done on the resulting images so far is digital
development,
> and only the values have differed based upon how I combined the
images. So
> far I've just played with the break-point in digital development,
and the
> values for the three aforementioned combinations were about 500,
1500, and
> 3500 for each, basically representing the differences in the signal
levels
> I've managed to produce.
>
> Anyway, I can definitely see the nebulosity but there are just too
many
> stars to see it clearly. I've seen other shots of the Veil that
didn't have
> so many stars in them, and had a much clearer rendition of the
nebulosity.
> Is this just fancy processing, like masking the images so that the
stars
> don't show up so prominently? If there's more to it than that,
what am I
> missing?
>
> Here's a link to a JPEG version of what I have at the moment. This
is about
> 1/4 of the original frame, or a 1536x1024 image if you view it
at "original"
> resolution.
>
> http://www.pbase.com/image/23629356
>
> Any suggestions?
>
> I'm not sure where I could place a full resolution TIFF of the
unprocessed
> version if someone wanted to give it a whack. It's a bit over a
9MB file
> uncompressed, and still about 7MB zipped.
>
> --Greg
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