I like working with shadeless materials using the import images as planes feature, it means that I can use photos for matte paintings and help with composites. When I used to use this in BI the speed to render a frame that featured only shadeless materials was pretty instantaneous but in Cycles it is like any other rendering.
So for example I have a bunch of planes, all using the Emission/transparent material set up that is created by the Import Images as Planes addon, and when I hit render it takes 2 minutes 40 seconds to render a 1080p frame. Compare that to the same setup using BI and it takes 2 seconds to render.
Is there a setting I need to turn off in the passes for the render layer or is this just a by product of the Cycles rendering engine method of rendering? It’s the same when it’s rendering any completely transparent areas, if nothing is there why should it take so long to render nothing?
Cheers for any replies
EDIT: OK I’ve found the solution, for anyone who might be having the same problem
The reason the shadeless material is taking so long to render is because it is rendering with the same amount of samples (150) as the other elements in the scene, where as the shadeless material only requires 1 sample to render correctly.
As my shadeless materials are all on their own Render Layer I can Override the samples for that Render Layer using the Samples setting in the Render layer settings. So on the layer with my Shadeless materials I can set the samples to 1 and it renders in seconds.