One difference could be the pressure on the pen (stronger when scribling) with more relief in the scribbling. Perhaps a raking light is enough for inspection with the naked eye otherwise taking a picture (of either side of the paper, possibly the opposite side if there is nothing on it) could provide a mask usable to dim the scribbling. A scan could be a ...
You can use a layer mask to do that.
Open the image of John Lennon in GIMP.
Open the image of the squares. Do Select > All and then Edit > Copy
Back in the John Lennon image, hit the "Add a mask" button in the layers panel, then in the dialog that appears, hit "Add".
Do Edit > Paste, and hit the Anchor button in the layers ...
You can add a layer, filling it with the desired color or pattern and use Gimp Layer Modes to obtain the desired result (Lighten Only should work).
Starting from your image (I've borrowed it from your screenshot, so the contour is a little pixelated):
You can add a layer with the desired color and set "Lighten Only" (your image is black) as ...
Colorize won't work on a totally black image unless you adjust the Lightness slider. If you set it to 0.5 it should match the sampled colour.
Anyway, If you want to colour that image with a sampled colour, I'd employ a different technique that avoids messing with sliders. The following will work with any solid image with transparency, regardless of colour.
Colorize typically maps a range of luminosity to a black-to-color-to-white gradient (in other words, its maximum effect is on midtones). In your image there is only black, so it remains black, unless you push the lightness a lot but this will still give you something a bit darker than your color.
If you want to replace the black by another plain color, just ...
Looks like an XY problem. Gimp isn't Paint, and Gimp has layers. If you want to paint a red ellipse on a green background, you use two layers:
one where the ellipse is surrounded by transparency,
one completely filled a uniform color
Is actually this:
The background layer is masked off by the ellipse. On the rim of the ellipse, there are ...
You may be able to extract the old filter from an older copy of GIMP, but no guarantee it will still work in newer versions of GIMP. You can download old stable versions from the GIMP website: https://www.gimp.org/downloads/oldstable/
Edit: Further to comments, the sharpen filter for GIMP 2.8 on Linux seems to be located in the following folder: gimp-2.8.22\...
Choose the Ellipse Select tool, and uncheck "Antialiasing" in the Tool Options.
Then when you make the ellipse and fill it (Edit > Fill with FG/BG colour), the colours will be solid. Note however that doing so will make the shape edges jagged, which is why antialising exists, to give the illusion of smoother edges.
GIMP has anti-aliased the edge. That's about 1..2 pixel wide zone which is partially transparent (if you have otherwise transparent layer) or partially mixed with the background. Without antialiasing edges look jagged.
You have several methods to make non-antialised shapes in GIMP:
paint with a hard edged brush (Maybe not especially good option if you need ...
GIMP has no spot colour channel support, nor does it support CMYK images used for print separations. To be honest, GIMP is not ideal for print work. Also note that CMYK printing doesn't involve the use of white Ink. So you'd need to check that requirement with your print supplier to find out what's possible. It would have to be created in such a way that a ...
Select your required area
Invert Selection (to re-select your desired area)
Image-> Crop to selection
Undo all above to return to original image
Repeat for each required area export
To permanently disable layer boundaries from the File > Preferences menu chose Image Windows > Apearance to untick Show layer boundary. This then works on all newly created layers.
To toggle visibility of layer boundaries create a keyboard shortcut from Edit > Preferences > Interface. Select Configure Keyboard Shortcut and scroll down to the ...
GIMP doesn't support that kind of layer clipping and isn't fully compatible with the PSD format, but there is a simple work around.
If you put the fill and smudge graphics within a layer group, you can set the blending mode of the filled layer to "Screen", and it will not affect layers below the group.
Note that GIMP has its own native ...