Hair and density image texture

why when using an image texture for hair density , the amount of hairs stipulated doesnt appear where the white in the texture is , only a few hairs appear and the amount has to be ramped up ,
example , for some eye brows i used an image texture but then had to use 20 000 hairs just to get some decent brows appearing .?

thanks in advance

Would help to see a .blend file that demonstrates whatever you’ve done. Don’t make us guess.

Ha I just came on here to ask exactly the same question!
My description of the issue:
When the location of hairs is controlled by a texture, the number of hairs you specify does not appear.
Blender seems to include the zero length hairs in the total count, so to get the correct number of hairs in the texture painted area it is necessary to specify an absurd number of hairs.
Eg if the non-zero area of the texture is 5% of the whole area, you need to specify 20x the actual number of particles you want.

I also found another issue (I am using build 60294):
Interpolated children don’t seem to work when using a texture to control density.
Simple and no children work.
Try selecting none/simple/interpolated children in the attached .blend and see what happens.

fur_tex.blend (607 KB)

is this really an issue that only two people have encountered ?
would other people be using weight paint only ?
is it not easier to use textures to control density , especially when working with hi res mesh.

If the total area you want to grow hairs is as small as 5% of the total mesh surface, an image like that is really the wrong approach. In that case there’s no good reason not to use vertex groups. Remember, you’re trying to use the texture to control density, not location. There’s a subtle but important difference. If you have a wide area of your mesh where you don’t want hair, just don’t include it in the hair in the first place. Don’t control that area with a texture. Controlling density with a texture is really intended for controlling variable density across a hair-covered surface, not to just define the one tiny area where you want hair.

Also deepee I can only assume that Py_'s demo file is an accurate depiction of whatever you’re experiencing, since you still haven’t provided one yourself.

yup its the same problem,
guess thats solved then ?

cheers people

I’ll just also note that you can tick the Use Modifier Stack box and the hair system will take into account things like SubSurf, which will make your vertex groups that much nicer in the end. Save image texture density control for something like a dog whose fur is thinner and shorter on its legs and belly, for instance. For things like eyebrows, stick with vertex groups. Even then, you can use weight painting to get a variable density and length texture.

K Horseman,
you gave, as your usual, a clear and exhaustive response and, by the way, you taught me of the Use Modifier Stack, that puzzled me several times before, thanks.

Maybe it is not enough evident from your answer that you can actually use both, vertex group and density texture, so that the first delimits the place and the latter refines the proper shape, even on low density meshes.


Good point. I was kind of thinking in one-or-the-other terms, but you’re absolutely correct. For example, this would be a good technique for something like facial hair. Define the general region with a vertex group, then use a texture to vary the density. You could even use multiple textures and control things like kink, length, clumping, and so forth. At least, I know this can be done in BI. I’m sure there’s a way in Cycles, but the technique is no doubt somewhat different in the details and I haven’t tried it myself.

That’s a better idea, I will also use that approach for my project.
I’ll test tonight if that also fixes the interpolated children problem I described.