Re: [APML] Sagittarius Reprocessed (105mm)

[Vicent Peris <vicentperis@ya.com>]

Brian,

you can go to this pair of websites for learning about vignetting and sky
background correction:

www.astropix.com
www.pleiades-astrophoto.com

And about the Unsharp Mask, I like to do an USM with a large radius (of
50 pixels or more) with my images. For example, for wide field images,
this makes the dark nebulae more intense. But first I select the high frecuency
details on the image to assure that the USM will affect only to
very low frecuency details. Selecting the high frecuency details
can be done by:
- Make two duplicates of the image.
- Blur them, one with a small radius (1 or 2 pixels) and the other with a
larger radius (10 or so, always depending on the image).
- Next substract the image blurred with a larger radius from the image
with the smaller one. You will get only the high frecuency details on the
image.
- Adjust the levels, saturating this image, and blur it a bit. This will be
the mask that will select only the low frecuency details of the image.
- With the original image, go to select > load selection, and load the
mask you have done, and pick on "inverse".
- You can now make an Photoshop's USM, going to
Filter > Sharpen > Unsharp Mask.

I have tried this on your image, you can view the results at:
www.cepheusastrophoto.com/Brian.jpg

Enjoy!
Vicent.
At 14:42 24/02/2003 -0600, you wrote:
>Thank you Vicent,
>
>I am stumped how to make a color balancing gradiant like that...I remember
>awhile back reading an artical relating to the subject, but I cannot for the
>life of me find it.
>I als tried the gradiant way back, but I was only using Photoshop LE.
>Now that I have PS 7, i can do much more
>
>I never heard of USM or the latter part of your message...I have always
>wondered how to bring out dark nebulae without sacrificing something else in
>the picture.
>
>If you can, can you explain the procedure to me or point me to a tutorial?
>
>Thanks,
>Brian
>
>
> > Nice shot Brian. Perhaps the green background at the bottom can be
> > corrected with the appropiate gradient; you can also try to make an USM
> > with a very long radius, masking before the high frecuency details, to
> > accentuate the dark nebulae.
> >
> > Vicent.
> >
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