[Leica] Help: Contrast management in Photoshop

[Martin Howard <mvhoward@mac.com>]

I have a problem that occurs relatively frequently and I'm hoping that 
some of the Photoshop wizards among you can help me out.

Occasionally, I need to increase contrast locally in an image.  For 
example, the face in an environmental portrait may be a bit flat, i.e. 
it only spans a few levels from the darkest to the lightest pixels.  In 
a darkroom, you'd fiddle this with dodging and burning typically 
combined with a different grade contrast filter on VC paper.

However, in Photoshop, I'm lost.  What I'd ideally like to do is get 
Photoshop to do is two things: pull apart the end points in a local 
region (masked off by a selection) and then "fill in the blanks" in the 
resulting histogram so that I get a smooth tonal gradation and no 
posterization.

Is there any way of accomplishing this?


I suspect there is -- because I've noticed something else interesting.  
I've taken to do a quick preview of my scans using "Preview" (the Apple 
application bundled with OS X).  It manages to do something remarkable: 
When you first load an image, it looks grainy and harsh, with 
semi-posterized areas.  But after about a second of calculations, it 
smooths out the tonal transitions, seemingly without loosing detail.  
The result is something that looks a hell of a lot more photographic 
than it did originally.  Since this is step two of the process outlined 
above -- and something that I'd love to be able to do in PS -- how is 
it accomplished?

M.

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