Rendering with a backdrop image - image gets stretched

Started by SteveR, May 10, 2014, 08:30:30 am

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Hi all, wonder if someone can help me.

I am rendering a planet in Terragen and I want there to be a background nebula type thing. I have got it all working by using an image map shader feeding through to a default shader for the background object, the camera projection is set to "Through Camera". The output render is the same resolution as the backplate image I am using (or an identical ratio when I am testing smaller renders). The position in the image map shader is set to lower left (default) and I have left the sizes as a and 1 (again the default values). 

The issue I have is that when rendered as a backdrop - the backdrop appears stretched - please see attached backplate image (full HD) versus a test Terragen render (not HD but ratio the same as the backplate) to see what I mean.

I am doing something stupid I am sure - but would appreciate a pointer!

Many many thanks


The image is projected on the background sphere, the image proportion can be left 1 to 1 if the original is a square image, but a tall image might  need to be 1 to 2 and a wide image 2 to 1 or 1.5 to 1.
I think your image needs roughly 2 to 1 for size settings.
So if you get distortion adjust with the x and y sizes.
You don't have to but if you select the type of projection to Position Center type, then also setting the image positions to x 0.5 y 0.5 moves the image so the center of the image is at the center of the camera projection.


Thanks Fleetwood,

That's helped loads - got it sorted now thanks to your pointer! I centred it as you said, and used sizes of 1, 0.561 to get a fairly close match to my full frame backplate (which is basically 2:1 as you said!) . Rendering out as I speak but the quick lo-res tests seems to show it was fine. So many thanks :)



I wonder what would happen if you use a huge plane as a backdrop and delete the background node.....