Wrong diffuse color darkening by the fresnel effect during layer output

[Micha]

Hi,

I render a simple test - a shiny plastic shere in a HDRI environment. I save render layers for the image components and I have the problem, that the diffuse color is darkened by the fresnel reflection effect.This cause, that at the final composited image, if the reflection layer is blend out, the color of the sphere looks wrong. Is there a way to get a render layer of the diffuse colors without influence of the reflection effect? If not, please add an option. (I use Vray for Rhino - or is something wrong with the diffuse channel output of VfR?)

I think, the diffuse color should be unaffected, but the transparency of the reflection layer transparency needs to be controlled by an extra layer. I looked around and if I understand right the ReflectionFilter channel should do it. So the only question is - how to get a clear diffuse color channel (could be named Raw Diffuse).

Ciao,
Micha

[Dariusz Makowski (Dadal)]

Umh Im confused.

Diffuse is pure Texture/color. Do you mean light? I cant read german. Do you blend in 32 bits? From the sphere u should use Light + refl in additive mode. If u want to use diffuse pass you need Raw Light multiply by diffuse and then Add over that reflections. Or ig u want raw reflections then diffuse pass multiply over raw refelctions if I'm not wrong and then add over raw light... Not sure if we need refl filter tho. Cant remember.

[Micha]

I did the layer functions like you sayed, only I have no lights in my scene, so I don't used a light layer - diffuse+GI+reflection is used.

The problem is, that the diffuse color channel shows a fresnel-like darkening at the sphere, but at the diffuse layer the green sphere should be a homogeneous green disk only.

[Dariusz Makowski (Dadal)]

That wont work. You have max Default light enabled. So you still get light from default light.

Just render Light + refl and screen them in 32 bits and ull get match.

or do Diffuse Multiply Raw Light Screen Diffuse Multiply Reflections (I might be wrong on reflection part) and that should match ur beauty in 32 bits.

[joconnell]

What are the names of the passes you're using for this comp?

[Micha]

Layer names are Diffuse and RAW GI and Reflection, all are 32bit, composite looks like the full rendered image, there is no the problem.

The problem is that the diffuse layer shouldn't be affected by the fresnel effect, all colors should be shown as plain colors without any shading, because if I disable the Reflections at the composite layers, than the diffuse color shows the wrong looking fresnel darkening.

EDIT: default light is off, I'm sure, light layer is really black.

[joconnell]

I getcha. What happens quite a bit with vray's sampling is if it doesn't contribute much to the final pixels, it'll often not get sampled at all - at the edges of objects with fresnel reflections, the reflections are up at 100% strength which blocks out all of the diffuse, so vray doesn't write any data into those edge pixels. There has also been some issues with the raw passes not behaving themselves properly, most notably in the reflection channels so you're often better off making your own by dividing the lighting channel with the raw lighting channel, this doesn't seem to work as nicely in the diffuse though. The only thing I've gotten to make it better is by turning down the level of reflections so that it has less to remove from the diffuse filter. It might be something to do with the anti aliasing but that's for the chaos guys to look at.

[Micha]

I don't talk about a thin bad sampled edge .... here one more example. I faked the right look per PS, the rendering shows the darkening caused by the fresnel reflection.

[joconnell]

Yeah I see the same thing - if you turn on the reflection filter pass which acts like an alpha for the raw lighting, you'll see a similar gradual fade into white at the edges rather than just the outline of the object.

[Micha]

The question stays ... could the a diffuse color channel without fresnel effect be added please?

[Svetlozar Draganov]

We are sorry for the delay - we've added this into our bug-tracking list and we'll inform you when we have it fixed.
Thank you very much for your feedback.

[Svetlozar Draganov]

I got a feedback from our developers - they informed me it would be very easy to get diffuse without fresnel effect by dividing the diffuse render element by the inverse of the reflection filter.

[Micha]

Do you mean it could be added as extra output channel for the next releases or should it be done in postwork?

I tried it in postwork. Attached my result with a non-inverted reflection filter - the only way I found. The antialiasing of the edges looks not so good. What do you think?

[tashko.zashev]

Hello Micha,

What are your AA settings? Can i see your scene setup?

Here is a screenshot of the result i get in our environment:

[Micha]

Hi Tashko,

attached my two channel output images from Vray for Rhino. I think this kind of correction in postwork will bring some disadvantages. Better would be to get the diffuse channel without fresnel information and to use the reflection filter channel for darken the diffuse channel if needed.

Ciao,
Micha