02-03-2017, 05:45 PM
(02-03-2017, 03:45 PM)Ofnuts Wrote: Thinks of your image build by stacking sheets of glass on which you paint things. Each sheet is a layer.
The Layers dialogs shows you how they are stacked (so you can change the stack order). It also tells you which are visible (ie, actually in the stack) By clicking on an eye icon you can make a layer visible/invisble (ie, temporarily remove it from the stack).
The RGB channels are there mostly for display. You can also copy them to plain channels by dragging them down or enable/disable them, but this has little purpose. The main purpose of the channels dialog is to manage the channels you create (by saving selections, mostly).
The alpha-channel is a fourth image component (besides the R,G,B ones) that controls the opacity of the pixel. You don't choose a color to be transparent. A pixel is transparent because its alpha value is 0, whatever the R,G and B values. A pixel can also be partially transparent if its alpha is less than 1.
Transparency is edited implicitly or explicitly. When you use the eraser or use Edit>Clear, the alpha value is set to 0 (if you are using a soft brush fro the eraser, the alpha can have an intermediate value). If you want to edit the alpha channel explicitly, you use a layer mask. This is more or less a companion grayscale layer on which whatever you draw/paint is interpreted as the alpha channel of the "parent" layer.
Thank you for responding. You say
'The alpha-channel is a fourth image component (besides the R,G,B ones) that controls the opacity of the pixel. You don't choose a color to be transparent. A pixel is transparent because its alpha value is 0, whatever the R,G and B values. A pixel can also be partially transparent if its alpha is less than 1.
If I cannot choose to make a colour transparent. How would I make the background transparent?