Portrait (Blender and LuxRender)

[mcz]

I lost a week to try to understand how to represent transparencies with LuxRender. Finally I got the right answer in the Blender.it's Forum.

So I decided to see the difference between Blender internal motor and LuxRender.
The image is naturally the same and the same are the textures and the two lamps (one point light, without shadows in Blender, and one spot light, both with energy = 1).
I changed in LuxRender only the reflection value of the lips after the first rendering.
The transparencies are made with transparence masks both in Blender and LuxRender.
For the eyes in LuxRender I've used glass (with 'architectural', also if the rendering was made with bi-directional).
Both images are in the format 640x512.

Here the result:

The left one was made with Blender's engine (rendering time: 9h and 25 minutes), the right one with Blender (20 minutes for 207 S/px).

[jeanphi]

Hi,

Nice image, congrats! And that's one of an interesting comparison too.
Did it really took Blender 9h to get this result with only 20min for lux? That sounds backward, but if so it'd be interesting to let the lux image clear a bit more.
I'd say this kind of scene is asking for subsurface scattering. The skin shadows are too sharp and it is amplified by your use of point lights. The shadows on the hat are really great though.

Jeanphi

[Carbonflux]

I agree with everything jeanphi said above, very interesting

My one comment would be that until SSS is implemented I have been using a matte 90% + glossy 10% mix for skin and setting the absorption really high and while this does not exactly give you the kind of slimy/wet/plastic skin tone SSS will give you it does seem to do ok in terms of what the camera sees.

The problem with skin is complex imo, its transparent and reflective and it absorbs light.

Honestly I would prefer another solution to SSS which I view more as a procedural texture then a simulation of actual organic material but that would mean modeling everything under the skin heh.

[mcz]

Yes, blender worked for more as 9 hours with full 4 threads.
And that was my first surprise.
In 8 hours I get a full 2560x2048 picture with LuxRender (with 300 S/px).
There are also some differences on the hairs (specially over the shoulder on the rights side).

The punct light is suerly wrong. Pherhaps an emitter with a semi-cilindrical shape could replace the two lights.
I have no idea what a surface scattering ist and what for effects it has. But I can try it and have a look on what happens.

P.S.: the skin is an high-resolution jpg. And I put the the specularity = 0.
Pherhaps I could try with a greater specularity.

[jeanphi]

Hi,

The punct light is suerly wrong. Pherhaps an emitter with a semi-cilindrical shape could replace the two lights.
I have no idea what a surface scattering ist and what for effects it has. But I can try it and have a look on what happens.

Maybe you could try just replacing the point light with an area light (even a simple rectangle should do I think) just to soften a bit the shadows. I think the spot can maybe stay as it is.

Subsurface scattering is a feature that is still missing in luxrender. Here is a (I hope) simple explanation applied to skin:
- when light arrive on skin, part of it is directly reflected but part of it goes through the skin
- light going through the skin will then meet organic material like fat, flesh, blood that will absorb part of the light or reflect (scatter) part of it in various directions
- light will then eventually reach the skin again and go out, but at a different place than it entered the skin and with a different color

This is the reason of blush when you have emotions (you see more blood through the skin) and that's why you can see light through your hand in the dark (or get a funny face by putting a torch under it ). It is also the reason why shadows are usually really soft on skin: even if there is an abrupt change in light intensity, part of the light will enter the skin and go out in the unlit region.

Jeanphi

[mcz]

Thank you, Jeanphi for the explanation. Very clear, indeed.

[psychotron]

nice work mcz, I like luxrender output.. your skin shader is fine for me even without SSS (but of course I looking forqward SSS implementation in luxrender)
is this hair a particle system from blender? can luxrender render particles yet? I thought it can't

[mcz]

No.
The hairs are surfaces with a transparent texture (image-jpg with a transparent mask), so as the hat.
The hairs are not full right with LuxRender. You can see that with Blender internal engine they are better, but also with LuxRender they are acceptable.
Also the hat is rendered different by Blender.

Now I'm rendering a full image (2560x2048) with an area light so I can see the difference with the same image with punct light.
Then I will upload the best one to the gallery.

[mcz]

I downloaded the portrait and a new scene.