Gradiented backdrop loses quality when rendered

ancanar_3dfb1cf89d

I downloaded a gradiented image from free archive to use as a backdrop but no matter what resolution and settings i use it renders in worse  quality than it originaly was downloaded. Below i am attaching links to both downloaded and rendered images of the backdrop only and as you can see the rendered one is much less smother. What is causing this and can it somehow be improved?

Links:

unXPctD.jpeg (6000×6000) (imgur.com)
myYwHPN.png (945×1080) (imgur.com)

Richard Haseltine

Both gamma correction and any tonemapping will adjust the colour vlaues of the image, which will have the effect of at leasts lightly posterising the image (all of the colour values are used, so moving two clours closer together will merge them and leave a gap below them - you can see this if you prform similar adjustments in asan image editor with the histogram open). I am surprised the effect is as obvious as that, but it does depend on your settings. Truning gamma to 1 (needs Tone mapper Settings node in the scene, render or use the Create menu) would reduce the effect, using the Canvasses section in render Settings>Advanced and adding a beauty Pass would allow you to save an .exr file with higher bit depth colour information which should be much better.

ancanar_3dfb1cf89d

I turned whole tonemapping off  and it is even worse now (see link). So i guess it was not the cause. Any other ideas?

jz0VW1O.png (945×1080) (imgur.com)

Richard Haseltine

If you look at that image's histogram it isn't terribly smooth to start with, though the rendering does certainly seem to exaggerate the effect.

NorthOf45

Banding like that is usually a symptom of the colour bit depth and/or compression on the output. 8 bits per RGB channel is not enough.I have not been following image-related developments, but 10-bit (I've seen it mentioned somewhere) would give four times the resolution in terms of colour per channel.