09-26-2018, 08:26 AM
Quote:The red blob is now SHEER, as if it was a stained glass pane. Need more proof? Here is a boldly-patterned image:...
It goes back to nothing in Gimp is accidental, It all comes from the user.
Quote:..If you can tell me what happened here, so that I can reproduce it at will, I will be eternally grateful!
This example (using Gimp 2.8) top to bottom, using the same colours as your screenshot. There is a selection in place.
https://i.imgur.com/oATDU00.jpg
1. If you colour pick the 'red' you will find it is not pure red, it strays across to the 'black' side.
2. A color-to-alpha (C2A) with black as the colour (white is usually the default) will remove the 'black' element leaving a semi-transparent pure red behind.
3. That lets any layer underneath to show through.
What essential are you missing? You can change the C2A colour by clicking in the dialogue, then select some other colour, including color-pick that off-red. Which will give total transparency of the selection.
https://i.imgur.com/09kmkJM.jpg
You might not like any mention of masks, but the alpha-channel for image transparency is essentially a built-in mask. You can not really have a transparent image, your software has to use that mask (and some do not)
I know the Gimp docs https://docs.gimp.org/2.8/en/ are not easy to trawl through, but all the essentials are there. https://docs.gimp.org/2.8/en/plug-in-colortoalpha.html
If you do not like the on-line help and a Mac is unlikely to get local help installed, there is a good pdf, with a searchable index, here: http://gimp.linux.it/www/meta/
Going back to one of your earlier posts. Jpeg images do not support transparency. Save all your work-in-progress as a Gimp .xcf file. Then export as a png which does keep the transparency.