Why does Arnold render some frames with banding?

[Dan_Lewis]

I have a project which renders some frames with banding and other not?

[lee_griggs]

Give us a look. In the picture viewer or IPR window or after saving the image?

[Dan_Lewis]

Thanks Lee - can you see these images large enough. If you look at the babies leg there is banding on frame 19 but not 20 – it seems to be happening randomly. One render I did was banding all the way through until the final frame which was perfect. There is also an issue with me getting these renders into aftereffects as they come in way too dark which I assume is because they are linear rather than sRGB but I can figure that out either.

[lee_griggs]

Do they look like this if you render out to EXR? Do they look like this in the IPR/Picture Viewer?

[Dan_Lewis]

Same issues if I render to EXR too. They look fine in the IPR and Picture Viewer.

[Dan_Lewis]

Hi Lee - I have noticed something after trying to render it out again, if you look at the attached screenshot - the green bar goes from 16 frames to 75, they have all rendered fine, 1 - 15 that aren't in the green zone are all banded. What's that all about, is that cached images in the green?

[peter.horvath6V6K3 · Accepted solution]

I believe it's the cache in the Picture Viewer. The green zone are the cached images in the memory, the grey zone are the cached images on the hard drive. Images are rendered into a 32-bit buffer, but it seems like when they are loaded back from the hard drive cache, they are 8-bit, which is causing the banding.

But this should have no effect on the images you save out with the render, this is just the cache displayed in the Picture Viewer.

[peter.horvath6V6K3]

I had no issues when rendered to EXR. Did you use the Save in the Picture Viewer or an Arnold EXR Driver?

[Dan_Lewis]

Hi Peter - I saved the exr out of picture viewer. I think the picture viewer cached images on the hard drive must affect the saved images. I’ve increased the memory the picture viewer has access to in preferences so it can now cache all images in the memory and now I can get all images out without banding.

[peter.horvath6V6K3]

Thanks for confirming. I'll ask MAXON why the cache behaves like this, don't think it's normal. Maybe I'm missing something from the plugin.