Polarizing filter for the VRayPhysicalCamera

[Art48]

Hi,

Is it possible we get a polarizing filter for the VRayPhysicalCamera?
My boss (a photographer) recently asked me this.

In my mind it wouldn't be that difficult to implement but then again I am no programmer.

What do you guys think? I'd definitely see a use for it when doing environmental shots, maybe even cars to make the paint pop more.
Is in-camera the best way? Or maybe a post effect? I don't know.

[Macker]

You'd have to trace the polarity/phase of every ray of light?!

[White Wizard]

I imagine Vray would need to add an additional property to every single Ray it fires storing it's rotational orientation in one local axis and then also calculate this orientation flipping or changing with every interaction.

Seems like a lot of code to implement but I'm no expert. Meanwhile you can get a similar effect by creating separate passes for the different reflections and lights to mess with in compositing for a similar effect. Having environmental reflections on a separate layer for example will allow you to adjust the intensity of reflections on leaves/trees/water/Windows much like a polarizing filter does for exteriors.

[Art48]

Hm. I thought it would be just some vector maths treating the rays with data already available? Dunno. Maybe a simple version? Although I'd definitely prefer a physically accurate version.

[werticus]

you would also need to know what materials affected the rays and how they did it.

[joconnell]

This is pretty much what you get by rendering in passes anyway - you'd wanna look at a demo by one of the photoshop guys in taylor james or mackevision and see how they treat their render elements.

[Art48]

This is pretty much what you get by rendering in passes anyway - you'd wanna look at a demo by one of the photoshop guys in taylor james or mackevision and see how they treat their render elements.

Thanks for the pointer, I'll have a look.

So the gist here is that you do not think that is a good /worth-the-effort feature? I'd love to hear some developer input, too on this.

[joconnell]

Well, if the point is to have art directable control over the amount of reflection all through your scene, that's already there in the render passes. With a real life polarizer is it not a bit hit in miss in terms of you need to rotate the filter to get the desired result on one part of your scene but other parts of the scene won't act quite as well due to it being driven by the angle of light going through the filter? Vray's passes and multimattes give you way more control than that in any part of your image.

[Art48]

The point for my boss is he always wants stuff "as real as possible" in terms of technology regarding the cameras and lights. I think in the end it is just easier for him to use the stuff he knows from photography.
So you would suggest I propably take the reflection element, put it on top with subtract blend mode and paint my polarized filter effect in, right? I don't know very much about the reallife pendant, but is it really all that it does?

[joconnell]

Yeah, polarizers will generally remove haze and reflections and increase contrast and saturation. If you did a simple rebuild of your scene from the main elements in photoshop, you could dial down the reflection and specular layers and pop on a few adjustment layers to get similar results.

[White Wizard]

The point for my boss is he always wants stuff "as real as possible" in terms of technology regarding the cameras and lights. I think in the end it is just easier for him to use the stuff he knows from photography.
So you would suggest I propably take the reflection element, put it on top with subtract blend mode and paint my polarized filter effect in, right? I don't know very much about the reallife pendant, but is it really all that it does?

Essentially it gives you some control over which reflections to prefer. The most common use is to lessen reflections on glass, water, and leaves in the photography world. I'm a cinematographer and that's the biggest use I've found for them. They also work great for balancing a green screen. Outside of that polarizers are used in lcd screens to filter out light and create a viewable image, otherwise your screen would be pure white.

It makes much more sense to use render passes. If I had that option when shooting real life scenes, I would jump on it over a polarizing filter. They often cause unwanted visual phenomenon when used around man made light sources and such.

Set your reflection pass to add over your lighting pass. Opacity will control the reflection intensity. You can also create separate reflection passes for different light sources.

[Rens]

Yes it's easier to render out lights separately if you're looking for control.

If you absolutely want to render with polarisation you need to:
- Ultimately set up two renders, one for s-pol, one for p-pol.
- Set the light source amount for each render, for example you would have two different sky domes. (There's a band across the sky where polarisation is strongest.)
- Render both with materials where you can set the polarisation. For example using the reflector OSL shader I wrote.
http://www.rensheeren.com/osl/
- Now if you blend both renders 50/50 you should be back at your original render without polarisation setup.

Not the most practical, but could be fun to set up.

[crazy homeless guy]

The point for my boss is he always wants stuff "as real as possible" in terms of technology regarding the cameras and lights.

Does a polarizing filter create a realistic photograph? Or is it simply a tool that allows the photographer to control his image better, much like a render element is a tool that allows you to control you image better.

Tell your boss that you need to use the right tool for the job is akin to writing drawing on your monitor with a charcoal. Drawing on a piece of paper with charcoal is awesome. You know how it will respond to the movement of your hand, it looks great, produces beautiful images. However drawing on your monitor to get the same effect is not so bright.

[Art48]

Does a polarizing filter create a realistic photograph? Or is it simply a tool that allows the photographer to control his image better, much like a render element is a tool that allows you to control you image better.

That is actually a very good argument, thanks for that!