GraphicaBTW

[dinasset]

Another filter for 2.9.9
This one was initially inspired by a mural I've seen on my town:
the author -instead of painting the whole image- only painted:
- in white the lightest parts of the image
- in black the darkest parts of the image
I liked it.
Hence I created a filter which separates (using threshold):
- the values of the image between 0 and the first stop (default 85)
- the values of the image between the second stop (default 170) and 255
As BG i used a layer filled with a bricks pattern.
Over the BG there is a layer for the "whites" and the layer for the "blacks".
The intermediate values -remaining transparent- show the BG bricks.
So I got what I liked.
Afterwards I added some options to this filter:
- the possibility to use whatever BG is wanted by the user
- the possibility to replace white/black with a duotone:
  if the user has changed BG and/or FG colours, those two are used
  if not default yellow and blue are used 
- the possibility to let the lightest/darkest values to maintain the original.
Here the filter.
Hope someone likes to test it.
Comments/critics/suggestions are welcome.

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[rich2005]

A little bit of testing I can do. Linux Gimp 2.9.9 A couple of screenshots:

The default B&W is quite effective, background shown inset https://i.imgur.com/Oi5Sfj5.jpg

Duotone, choice of colours does make a difference: first try red/green, not so good this one better. https://i.imgur.com/Gm6UyEI.jpg

[dinasset]

Thanks Rich.
Depending on the values distribution of the source image it could be useful to modify the threshold limits (default 85-170)

[Pat625]

Dinasset, I tried a couple.  I find that I went through several images before I found suitable results.  Here are my tries:
I liked the first set.
[attachment=1570]
[attachment=1570]
I thought the last set would have turned out better, but I could not get it to.
   
   

I think I need more practice with the adjustments to make the results better.

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I have one more set.  I liked the results.
   
   

[dinasset]

Thanks Pat.
I like better the "large flower".
From a pictorial viewpoint I like also the landscape, but I do not understand which parameters you used.

[dinasset]

Info.
Only to show the effects of what I suggested in a previous post (adjusting threshold values, set by default to 85-170).
Look:
original
default outcome
adjusting the threshold values to 127-223

[Pat625]

Have never worked with thresholds. I will play with it and see what I can do.

[dinasset]

Pat, I mean the "thresholds" in the filter parameters.
Look