Strange banding

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Mats78
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Location: Vantaa, Finland

Strange banding

Post by Mats78 » Sun Aug 29, 2004 11:21 am

Please take a look at my picture here. I'd really like to know if anyone sees any strange banding effects. I experience some and can't seem to get rid of them. I'm on Linux and using Xorg with 24 bit color depth (eg. different color transitions created with the Gimp all look fine, no banding whatsoever).

Is this a blender feature/bug/error? It also happens on windows. Versions tested: 2.34 and CVS from yesterday + tuhopuu today.

Very annoying =( Oh, and the pic is the default Blender scene. Just moved the camera a bit closer to the box.

Thanks,
mats

Image

lucky3
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Joined: Thu Oct 17, 2002 6:08 pm

Post by lucky3 » Sun Aug 29, 2004 7:02 pm

Yes I've noticed that too, don't know why.

tuinbels
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Post by tuinbels » Sun Aug 29, 2004 7:12 pm

That also happens here, with lamps of type Lamp and Spot. It doesn't happen with area light, hemi and sun light. And then only with flat surfaces, when turning on SubDSurfaces for the cube, the banding disappears.

So the only useful thing I can say is not to use lamps and spots when you render flat surfaces...

meestaplu
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Location: CT

Post by meestaplu » Sun Aug 29, 2004 7:52 pm

I did some more in-depth investigation on this, and it looks like the banding comes from the limitation of an 8 bits per channel image. As you move along the bands, the colors in each band could not be any closer together:

R: 62
G: 62
B: 62

R: 61
G: 61
B: 61

R: 60
G: 60
B: 60

R: 59
G: 59
B: 59

etc.

Dithering when the image is converted to 8 bits per channel could solve this problem.

Matt
I love vector calculus at 4 in the morning.

Mats78
Posts: 100
Joined: Thu Oct 17, 2002 5:06 pm
Location: Vantaa, Finland

Post by Mats78 » Sun Aug 29, 2004 8:15 pm

Ok thanks. Must be because I just bought a new monitor... I guess my old one really did suck as this went unnoticed for so long =)

mats

joeri
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Post by joeri » Tue Aug 31, 2004 12:19 pm

Dithering when the image is converted to 8 bits per channel could solve this problem.
Isn't the blender renderer a 24 bit (3x8) renderer ? So there is no "converting" ?

If rendering for print add a little noise to your picture.
When printing to film the (film)grain is added automaticly.
On NTSC, don't bother. it's Never The Same Color anyway ;)

I guess I should not give artistic comments.
But... a scale from mid grey to abit dark grey will have something like 16 steps orso, if thats spread out over more then 32 pixels you will see bands.
But if its a scale from abit blueish-grey to grey it will have more steps, and thus less bands.

I hope this makes sense.
So the only useful thing I can say is not to use lamps and spots when you render flat surfaces...
I think thats a very strange advice. Using no lights will also solve the banding problem.
But the idea of rendering is to get shaded sides.
Adding a noise or clouds texture will solve bands in solid faces.

TheAppleMan
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Joined: Sat Jul 17, 2004 10:31 pm

Post by TheAppleMan » Tue Aug 31, 2004 1:18 pm

I dont think its an error or problem, just diffusion.
It happens to me too and i'm not worried. I trust the devs somehow

~Apple

bfvietnam
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Joined: Wed Apr 21, 2004 8:54 pm

Banding happens..

Post by bfvietnam » Mon Sep 06, 2004 3:29 am

2^24 colors, is made by combining 256 shades of R,G and B. Everyone knows that.. But if you try to spread that out over an image that is 1280x1024, you will always get at least 4 pixels of banding per color, guaranteed.. I mean you can't count in fraction of a shade when extrapolating from 1 to 1024 with 256 possible values..

The only way around it is to render at high color depth.. Maybe using floating point representation internally.. It might make the math easier? Slower? Besides we need to go to HDRI.. This would be a good way..

Then just use a diffuse dither effect to approximate the shading in 24-bit.. Its like downsampling sound from a 24-bit representation to 16-bit.. Just for graphics..

As with what Joeri was saying, you could add noise.. Maybe use one of the other kinds of shaders for your material, I mean is that the default surface shader (blender-phong)?? You could also use a fine bump map..

As for NTSC, I guess having color cube transformations on the internal color model would be beyond reason.. However not all color can be reduced to RGB.. Might be too much to ask to use wavelengths of light in place of RGB..

joeedh
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Post by joeedh » Wed Sep 15, 2004 1:30 pm

Hi. I just wanted to say that I've gotten really good results by combining a fine bumpmap with the same texture also affecting *slightly* either the color or the emission of the material.

Of course, getting a perfectly smooth spectacular highlight is difficult, but then again, for many things you don't want that anyway.

joeedh

levon
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Location: adelaide

Post by levon » Wed Sep 15, 2004 4:19 pm

yes ive had the same problem with this banding, i would assume its the 3D card or the drivers your using, it ony started when i had to re install windows xp and dled new drivers.

i have a Geforce 4 TI 4200

Friday13
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Post by Friday13 » Wed Sep 15, 2004 8:41 pm

levon wrote: i would assume its the 3D card or the drivers your using,
I don't think the video card has anything to do with this. It's about colors, and processing/display of the colors by Blender's renderer.

levon
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Location: adelaide

Post by levon » Thu Sep 16, 2004 6:32 am

its just before i reinstalled windows, i had now problem with this banding, and the only thing that would have changed was the drivers realy.

and i tested back to the 2.23 days, and it was the same banding, which i didnt get back when i was using blender on my old computer, or before i reinstalled.

though we should see if its happening to everyone, and anyone who does get these bands, we should find out what 3D card they are using and the driver versions.

IoN_PuLse
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Location: Canada, BC
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Post by IoN_PuLse » Thu Sep 16, 2004 4:14 pm

Friday13 wrote:
levon wrote: i would assume its the 3D card or the drivers your using,
I don't think the video card has anything to do with this. It's about colors, and processing/display of the colors by Blender's renderer.
Guess what actually does the processing of colours for the interface. The video card. (well, through drivers)

Try playing with driver versions and/or desktop colour depth.

Friday13
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Joined: Wed Oct 16, 2002 10:40 pm

Post by Friday13 » Thu Sep 16, 2004 8:41 pm

IoN_PuLse wrote:Guess what actually does the processing of colours for the interface. The video card. (well, through drivers)
But you can use Blender without a video card (via software OpenGL) and a computer does work well without one.

levon
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Location: adelaide

Post by levon » Thu Sep 16, 2004 8:44 pm

um actualy no you cant use blender with out a video card, in fact you cant even use windows or dos with out a video card.

your video card is what displays things to the monitor

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