At the moment it's happening with a long kilt prop. The prop has morph settings to alter its shape so it matches the character's legs. In most poses it looks fine. But in some (those where the knees bend more) it acquires a mysterious area of black, like an ink stain. The stain doesn't appear in the preview and only shows up when the thing is rendered. It varies in size: I have an animation where the character bends down, and the stain appears, gets larger, and then vanishes again as he stands up.

It makes no difference whether a texture is applied or not, or what other objects are in the scene. The only way I have found to remove the stain is to turn the Ambient colour to bright white. Effectively, the stain is the same shade as the Ambient colour. But of course setting it to white makes it look like the prop has been washed in some amazing soap powder.

So the question is - is this some peculiar flaw with the prop that I can't do anything about? Or is it some known problem that some objects have, to which there is a known remedy? Any ideas?

Something I've noticed is when you add a bump to any texture on anything that has folds/creases/indentations and then render it on the default render settings, you get that crazy black stain all across the area (its especially bad when ambient occlusion is on as well). What I usually do is set the bump down to anywhere between .001 and .005 and then customize my render settings (Irridance caching: between 70 and 90 - Pixel samples: 8 to 10 - Min. shading rate: 0) Thats my standard render setting.

Hope this helps a bit :)

Ana

I think the problem is caused by raytraced shadows. I also have seen/experienced the dreaded ink-blot of doomed firefly rendering. I seem to remember that someone advised me to increase the shadow bias. Personally, I found that tinkering with the lights was such a PITA that I mostly only use Poser for the posing and POV-Ray for the final rendering (of static scenes). I will also be watching the responses to see if there if a definitive solution.

Thanks for the comments. Alas, they haven't helped! It's nothing to do with textures (this happens when I remove them, too). And it's not just Firefly. It happens when I use the Poser 4 renderer too (I'm using Poser 6, by the way). It's nothing to do with raytracing either because I haven't got that on. Anasta, I don't have an Irridance Caching option, but fiddling with the others you mention doesn't seem to help.

Incredibly, though, the Sketch render options do not have the ink stain! Which is completely useless for what I'm trying to do. Ah well...

I did just do an image where I had to add forehead wrinkles to the face and no matter what I tried I kept getting the black line across it... I ended up having to reduce the amount of wrinkles because nothing else worked.

It may just be the prop itself, but I don't know for sure. Sorry, wish I could have helped more :(

Anasta, the problem you describe, artifacts due to even a tiny amount of bump, is because most people have misunderstood bump maps from the beginning. They are almost all gray. They should be mostly black.

See gray means 1/2. White means 1. Black means 0. This is true of bump or displacement. The number you type into the bump channel where you connect the map is multiplied with the map. So if you type in .1 inch, and the map is almost all gray, you're actually "raising" the entire surface by .1 * .5 = 1/20th of an inch. Now if you have a crease, like eyelid, lip corner, nostril, where the width of the crease is LESS than that 1/20th of an inch, then the surface "crosses" over itself and you get BLACK.

Curiously I have had to explain this 5 times in the last week. Usually its only once a week.

The solution when working with these mid-gray bump maps, is to use a math node and subtract .5 from it before plugging into your bump channel.