http://www.threebuttes.com/MaxImPhotoshopLayering.htm




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Subject:  Layering in Photoshop (was Re: New Image: NGC 2841)


  

Thanks, Dean.

I've been getting into this layering technique lately as a way to
display the whole dynamic range of an object with good contrast.

I suppose I should make a web page with pictures detailing this
method, but it seems like I already saw one one someone else's site
that was the same or a similar technique. Anyone remember who that
was?

Basically, it goes something like this:

- Stretch the luminance image until the faintest details are
displayed with good contrast. Convert to 8-bit mode and save as a
new .psd file. (The brighter areas will be completely burned out in
this image.)

- Starting over from the raw (16-bit) luminance image, do another
stretch that displays the next-brighter areas with good contrast. In
this image, the background will likely be very dark, and there still
may be some burned out bright areas. This is the "base layer."

- Convert this image to 8-bit mode, select all (ctrl-a), switch over
to the base layer image, and paste (ctrl-v). This will overlay this
new stretched image on top of the base layer.

- With the new layer selected, do a Select->Color Range. Click on an
area of the dark background, and then adjust the "fuzziness" slider
until you start to see parts of the object that are burned out in the
base layer.

- Feather the selection by some amount (say 50 pixels... depends on
the object) for smooth blending.

- Making sure the top layer is selected, hit the delete key. This
makes the dark areas of the top layer transparent and lets the base
layer show through.

- Repeat this stretching and layering process as many times as is
needed to cover the entire dynamic range of the object, each time
starting over from the original 16-bit luminance image.

- Tweak the histograms of the indvidual layers to get them to blend
seamlessly.

- Flatten the image (Layer->Flatten Image). Use this as your new
luminance image.

A couple of other tips:

- Use an un-deconvolved version of the luminance image as the base
layer. That way you won't have deconvolution noise in the faint areas.
Also, this seems to help remove any deconvolution-induced dark
circles around stars.

- You will probably want to decrease the amount of feathering for
each successive layer.

Different objects require different numbers of iterations of this
process, depending on their dynamic range. The NGC 2841 image
required four layers, whereas my H-alpha image of M42 required six:

http://www.rc-astro.com/nebulae/m42_halpha.htm

Best,

Russ
http://www.rc-astro.com


--- In SBIG@yahoogroups.com, "Dean Salman <junk@g...>" <junk@g...>
wrote:
> Great image Russ. Since you did not use DDP, I would like to know
> how you layered in Photoshop to resolve the core the way you did.
> Did you use the unsharpen mask as well, if so what settings did you
> use.
>
> Dean
>