[Gimp-user] how to darken bright areas

[paulhurm <forums gimpusers com>]

> On Wednesday 04 January 2017 18:58:20 paulhurm wrote:
> The black paper, and the glue, totally preclude any thoughts of its
> being
> an archival quality mounting medium.  There is some acid in all that 
> stuff that old.
>
> So you must do what can be done with the scans you have.
> You it appears, are truely between a rock, and a hard place.  The only
> other possible procedure would involved crafting a very narrow band 
> color filter, centered on the silvery tint, which might be further 
> filtered to recover its luminance detail, and re-add that detail to
> the
> K channel of a cmyk encoded copy of the original scan. I doubt that it
> could be scripted because of the variations in the aging of the 
> individual print. Under the conditions you describe, you would probaby
> have to separate each print on the page into its own file for
> individual
> processing. You would need to develop a filenameing convention that 
> included the page it was on, the upper left corner position marker,
> and
> the images own size, including any captions involved, so that once
> they
> were recovered as best as can be done, a relatively simple script
> could
> put it back together with everything in its original location for then
> making a single page image that could then be printed at high enough 
> resolution that other researchers could learn from it. 
>
> I don't envy that position...
>
> How about you make an "unsharp mask", crank up the contrast, then
> print
> with the unsharp mask subtracted to reduce the contrast back to maybe 
> 20% more than you started with?  That might find usable detail you 
> cannot see very well now.
>
> Cheers, Gene Heskett


I do have a bit of this already done. I do have each photograph as individual
scans, both with and without the captions and I am not too worried right now
about the final "reassembly". My current desire is just to get the issue
resolved with the quality of the prints. I already have ideas about "reassembly"
but not worrying about this step until I get better quality images.

As mentioned, I had a few steps accomplished once before but can't remember what
I had done. I still seem to recall having used an addin somehow and playing
around with luminance so that comment by you helps validate some of my current
thinking.

I think my next step might have to be to try to go through the various lists of
addins to see if I can find one that might help or perhaps stumble upon what I
used before.

I'm way too green to develop my own filter as you suggested above although the
concept you described seems good. I kind of had that accomplished in the
previous attempt where I did get the desired areas separated onto a separate
layer. It's just that I now have no idea what I did to get to that point. Thus
my post hoping for suggestions!!

Thanks.

Paul

-- 
paulhurm (via www.gimpusers.com/forums)