How to create a gradient backround in the compositor? I want to add a gradient background to my render, but within the compositor (not with the actual background world setting of the scene). I would also like to don't have to use an image (neither external nor internal) to achieve that.

I rendered my image with transparent enabled in film section of render panel. Then I tried to add a ColorRamp node with an Alpha over node, but now I'm stick on how to give a Factor to this color ramp.

My thought is to give it some coordinates corresponding to Y axis of the image, but I can't find a way to.

Is there a node that give some image coordinates ? (like mapping node in materials)
Add a Texture Node with a blend texture and color ramp. You can adjust the gradient using the Color Ramp in the Textures panel. (See image)