: Set transparency of wood print I am trying to make initials found in old books transparent. E.g. The paper should be completely transparent and the dark parts of the print fully opaque. But

@Vandalay110

You can actually try just layer->transparency->color to alpha and pick a medium color from the paper tone. This will make just that tone transparent, and preserve the texture noise, so that you can add other colors behind and still "feel" like it is paper.


To further remove "whiteish" pixels, just repeat the process picking one of the remaining tones - if you want the transparent areas to be completly clear, you can proceed to the mask/alpha gimnastics described in the other answers.


transfer alpha to mask
working on the mask do:


select by color on opaque area
feather selection by large amount
sharpen selection
feather by small amount
invert selection
fill mask with black

apply mask

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@Angela777

First, let me begin by saying I'm less familiar with Gimp than I am with Photoshop, but the concept works the same way. This is the best method I've found to easily create detailed masks.

Step 1: Prepare Mask



Boost the contrast between lights and darks. Desaturate and adjust curves.

Step 2: Create Mask



Select all and paste layer into layer mask.

Step 3: Clean up



With the layer mask selected, using the Dodge/Burn Tool, Burn shadows and dodge highlights. Invert the mask to activate the mask.

Result



After inverting the mask and adding a background layer, this is the result. Using a layer mask, you preserve the original layer.

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@Alves566

Alright I'll make this with limited screenshots since I don't use Gimp but I would hope this all exists in Gimp:


Convert to Black and White
If Gimp has it, tweak particularly the Yellow when converting to Black and White to remove a lot of it. (Update: Hue/Saturation... Yellow before we convert to B/W via Takkat in comments)
Then adjust the levels to further darken blacks and lighten whites
Convert Image Mode from RGB/CMYK to Grayscale
Then Convert Image Mode to Bitmap
Now if you want to be really precise zoom in and clean up the points in spaces that should be pure white/transparent


Hopefully this helps, the more you clean up the spaces in between / outside the better quality the final product will be. Here's some screenshots:

Bitmap:



Zoom in its actually not gray, just black dots:



Clean pretty easily clean up those black dots:

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