Paint.net blending from 1 layer to another
I have, through the years, used a paid version of Photoshop (back when I ran a photographic company that could justify the cost of Photoshop) then GIMP then I settled on paint.net for most of my image editing, other than AI based editing.
One thing I find I frequently have to do is have 2 images beside each other and blend from one to the other.
I thought I'd therefore share how I do that. It is done by blending with the gradient tool.
You start with 2 (or more) images on at least 2 layers
They have to overlap each other.
I will then be making one partially, in a gradient way, transparent. It has to be the layer on top, the bottom will 'shine through'.
It is important to know where each layer ends, so that you do not have the gradient transparency going past the top image at the 100% transparent, or in the other direction, past the lower image at the 0% transparent, otherwise you will have a 'sharp' edge where one or the other image is simply not there.
To start, click on the tool dropdown and pick gradient:
Or pick it from the toolbox if you have it open:
For this specific example, you will pick 'linear' as the mode
Then pick Transparency Mode
Here is my layer 'below'
And my layer 'above' (with the layer above turned off so it isn't visible)
Note the sharp line where the 2nd image overlaps the 1st
Bonus tip; Create a layer with marks that show where both boundaries are, you can delete it when done:
Bonus tip, when defining the transparency, you will often want to go 'perfectly' straight. This is easier if you start and end along, in this case, the top or bottom. Or if doing a vertical blend, the left or right edge, so you can stay lined up easily. Try it at a 45 degree angle to understand the problem this is solving.
Bonus tip: save the top layer, the one you are applying the transparency on, by duplicating it and then turning off its visibility. That way when you come back wishing you had used a different blend, it's more likely to be easy to change by deleting the blended layer and duplicating the source layer again:
Note that some images blend better than others. You may have to play with the overlap -more or less, to get your ideal blend.
If you want to blend the WHOLE image equally, without a gradient, it is trivial, just open up the layer and adjust it's transparency.