Gimp Alpha Transparency

Use GIMP to add alpha transparency to an image

While perfoming a Blender 3D tutorial, I needed an image with a blended alpha channel. The alpha channel would provide transparency to portions of the image and make it easier to manipulate.

Result of two point tracking tutorial

To create the effects shot above, I needed a cloudy picture of a mountain:


picture credit: Clare McDowall

…but the bottom portion of the picture needed to be transparent:


So I found an informative post in this forum with the key bits to remember:

To fade the gradient:

1) Make sure your current layer has an alpha channel
2) Go to Layer>Mask>Add Layer mask
3) when prompted to select a type, select "Layer's Alpha channel"
4) check to make sure you're set to edit the layer mask (it should default to this)
NOTE: What's going on is the "White" of your mask is the "visible", the "black" is the "invisible", and of course the greys are in between.
5) Set your foreground color to White and your Background color to Black.
6) Choose the gradient tool.
7) Set your Gradient to "FG to BG (RGB)"
8) Your White-to-black gradient is now the visible-to-invisible alpha channel gradient. You'll have to work with that to get the effect you desire.

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