Strange gradient side effect with material

Hello, this is my first time posting. I’ve looked at the forums in the past for helpful tidbits and I thought it was about time I join the community, so I’ll begin by asking a question.

In one of my recent projects, I noticed a very strange effect that occurred in the background. It seems that my back wall, which was a basic Lambert shaded material, has been rendered with a strange gradient in color. It looks like a high-color image that has been saved to a very reduced format (as though 16 millions colors has been reduced to 256).

I don’t think I’ve ever noticed such a side effect in the past few years that I’ve been using blender and I wondered if anyone has an explanation or a way I might get around such a problem.




Here’s the image.


Is this grey area the wall, or am I looking at a flat wall with a band across it? If so, then double check that you have no textures loaded, and check for any lights that have textures in them, like a blend texture.

The gray area is just the wall - all other elements have been removed from the scene. I’m using the internal renderer and the material for the wall has no textures and no color band. The basic material settings are shown below.


Do you mean the color banding?

If so, that is somehow a weird thing in Blender, as it seems. That topic comes up from time to time but I haven’t really seen a solution which works all the time yet. Maybe do a search for it on your own, with color banding as a keyword. Hope you find something and if so, please post your solution so that we may learn more about it.

(Increasing the dither slider was suggested sometimes but due to my own experiences, that doesn’t help at all…)

Simple, not enough grays. Use OpenEXR for very high-depth.

This happens when using Spot lamps set to Shadow Buffer with a too low number of samples.
Check if you have a spot lamp in the scene, and increase the number of samples.

You have only 24 shades of grey on a black background. This band can be a kind of optocal illusion:
Dithering might help, first try to set it at very hight value and then decrease. Or, you may consider rendering to some of HDR image formats.

I tried the dither solution, but that didn’t help. Also, I’m using raytraced shadows for my spotlights, but that certainly would have been a plausible explanation.

After looking at an older post, it seems that it’s an issue of too few shades of gray being available so I think masterhoshi and myn.pheos were right - I’ll look into an HDR format. Thanks to everyone for their suggestions!

my guess is that you are seeing JPG compression artifact. JPG is notorious for reducing color count esp. on smooth gradients like that. save as PNG lossless and compare.

I usually save everything as PNG, but I think I uploaded a JPEG attachment as my Picasa site didn’t support PNG. Interestingly though, if I save from Blender as a JPEG, although there are some artifacts and noise, it almost looks better.

Outside of using an HDR format, does anyone have any suggestions for faking it? I’m thinking about lighting the wall with a separate lamp on its own layer, so I don’t over-light the foreground (not shown).

smoother, more even lighting is my suggestion. you can tie the lights for the background to the layer the background is on and thus they will not have any effect on the foreground.

Please upload a .blend here:

I’d like to have a look at your light setup to see what’s going on. I had a file one time in 2.37 where, on every 4th frame, the shadows would render as wireframe for some reason and this completely baffled everyone. I don’t like to see this kind of thing go unresolved as Myke has suggested.

Papa is right. If you add more light, the most brightest spot will become even brighter, but if the darkest stay at the same value, the bands will be much smoother. Or increase the lamp dist parameter, or play with the quad1 and quad2 params.

Another solution might be to add some background, not a perfect black. That will distract you from the bands and add some contrast to the other area. It is almost innoticable if i open the image in firefor, on a white background.

I’ve tried to play with poorly lit models with desaturated colours, and the rgb output in render window was ok. It HAD bands, but the blender internal values (which are 32 bit) were very smooth. This banding is caused propably and only by image format, and the output device.

You are trying to fake hdri? That might be hard if your monitor can output 8 bits per channel. That’s very limiting when you are viewing hdr images, because in hdr image there is much more information than display can show. EXR has 32 bits per channel, and the best high-end monitors have 10-12 bits. So in rendered image you have billions of colours, but on display only few millions. So you can only see narrow range of colours at a time.

Also you eye cannot see the whole dynamic range at a time. Stay a few minutes in dark place and then go into the sunshine. For few moment you will be blind.