GPU versus CPU rendering in Cycles 2.64 and 2.65

Artistic Support Lighting and Rendering
1

I was doing some preliminary work checking that the gpu and cpu renders for our project were the same, since the team members noted that with another renderer they had used this was not the case.

I rendered some high sample frames from a scene and compared the cpu render to the gpu render by using a difference mix node in Blender and also the same difference mode in Photoshop. It seems that the only area where there is a difference is along high contrast areas in my uv mapped image textures.

I made a simple example to show here - one render is the cpu, one the gpu, and then the result of the difference. It seems to me if you load both images and turn the top one off and on, the uv image shifts ever so slightly.

cpu_gpu_difference.png960×540 8.06 KB

gpu_render1cube.png960×540 29.2 KB

cpu_render1cube.png960×540 28.8 KB

I was hoping someone could confirm this behaviour before I go about submitting a bug report. I did test this with 2.64 and 2.65 since we just got the new release.

Thanks a lot for any help!

2

It’s either a bug, or an anomaly (bug:D) of the different processes.

3

Bump

I wonder if anyone might try this out on their end so that we can rule out that this is a bug/anomoly rooted in the graphics driver local to my machine - it doesn’t have to be a specific type of texture, it can be any image mapped to uv coordinates, rendered out on gpu and cpu and compared with a difference setting in a color mix node in compositor. If this is a bug, I am ready to submit it as long as I have certainty this is not local to my machine.

Confirmed, submitted bug report. Hope that it leads to at least and answer about why.

And I got the message: Fixed in SVN :slight_smile: Awesome thing this Blender community