Correct workflow if CG object integration onto backplate... ?

[kosso_olli]

Would like to chime in on this one.

In picture one the teapot casts a shadow onto the ground, set to matte. As you can see, the shadow is nicely colored to somewhat match the backplate. Now I would like to get that shadow reflecting into the teapot. And ONLY the shadow, nothing else. In the first picture you can see the shadow, but also the gray material of the ground plane.

Now, if I set the ground plane to matte refl/refr, the situation gets better, but still not quite right. It looks like the backplate is projected and distorted onto the ground plane, causing a strange reflection. I would expect to see the HDRI and the shadow reflecting in the teapot, but not the ground it is standing on. Please take a look at the attached scene file.

matte_prob.zip

[LudvikKoutny]

Would like to chime in on this one.

In picture one the teapot casts a shadow onto the ground, set to matte. As you can see, the shadow is nicely colored to somewhat match the backplate. Now I would like to get that shadow reflecting into the teapot. And ONLY the shadow, nothing else. In the first picture you can see the shadow, but also the gray material of the ground plane.

Now, if I set the ground plane to matte refl/refr, the situation gets better, but still not quite right. It looks like the backplate is projected and distorted onto the ground plane, causing a strange reflection. I would expect to see the HDRI and the shadow reflecting in the teapot, but not the ground it is standing on. Please take a look at the attached scene file.

[ATTACH]19841[/ATTACH]

Well, what you desire makes no sense at all. What you want is having teapot floating in the air, and casting shadow on some invisible non existent geometry under it. I can not think of a single practical scenario where anyone would want that.

That being said, it should be very easily doable by just plugging environment map set to spherical environment to the self illumination slot WITHOUT any camera projection map. Of course, you also need to make sure no other material component, including diffuse (set it to black) is active.

[kosso_olli]

Well,
I just want the reflection on the matte ground plane to be visible in my reflective objects. The second picture is quite close, however I always get that strange transition from the ground plane into the HDRI, which annoys me quite a lot. If you got any tip on how to avoid that, feel free to share.

Also tried your tip with the spherical environment in the self illumination slot. It didn't work. How could it, as shadows can not be cast onto self illuminated objects... Again, if I am doing something wrong, please tell me.

By the way, your teapot image from the first page seems to be exactly what I am looking for. As far as I can see there is no transition, and the shadows look correct to me. How was it done?

[LudvikKoutny]

What's on your second picture is correct. That's the way it should look. That teapot isn't flat, but curved surface, so it obviously stretches reflection. Only difference is, unless you have super hi-res HDRI, if you project small part of it, it will almost always have quite low resolution.

Especially if you cameraproject something from such parallel angle as on your picture. Then you are reflecting very stretched pixels. What could help is disabling filtering of your HDRI or backplate (setting filtering in bitmap to none), or, of course, using higher resolution HDRI or backplate.

But again, what's on your second picture is correct. There's just not enough data on the projected bitmap because it was not shot from the angle, which is being reflected. I only rarely integrate chrome teapots, so in regular case of say Car integration, it should not be noticeable

Teapots on the first page are projected in exactly same way. You can see some stretching on the bottom going on as well, due to the curvature of a teapot combined with the factors mentioned above. And i am also not projecting from such extreme angle as you are

[kosso_olli]

Well, this doesn't work for me for a lot of reasons. For example, I have to render against a black background. As soon as I disable the background, the reflection from the matte surface is gone, too. Then I tried you tip with camera projecting the backplate using the self illumination slot, but that doesn't work because I can't get the shadow to show up on the surface. Man, this is a complete mess...

[LudvikKoutny]

Yes, i agree... Matte/Shadow solution in Vray isn't very well thought through.

I am also still waiting for an answer about why do not white teapots cast shadows on themselves on the picture posted by Vlado.

[LudvikKoutny]

Still no solution to this, i presume... :/

[vlado]

I am also still waiting for an answer about why do not white teapots cast shadows on themselves on the picture posted by Vlado.

Because I accidentally left the "Shadows" option off in the V-Ray settings...

Best regards,
Vlado

[vlado]

Yes, i agree... Matte/Shadow solution in Vray isn't very well thought through.

That's why this thread is so interesting. To be perfectly honest, the matte/shadow stuff is very confusing for me, because it seems that people are using it in very different ways and want different things from it... no-one bothers to explain very well what they need.

Best regards,
Vlado

[Wilyman]

That's why this thread is so interesting. To be perfectly honest, the matte/shadow stuff is very confusing for me, because it seems that people are using it in very different ways and want different things from it... no-one bothers to explain very well what they need.

Best regards,
Vlado

Admittedly, it's been a while since I've used another renderer, but to be honest, I feel the matte/shadow options in vray are pretty straightforward and work very well. And 90% of the images I produce involve its use.

This thread's shown that there were a couple of little areas in which it needed improving or clarifying, but I can't see any major issues with the way it works at the moment.

Cheers,

John

[vlado]

Because I accidentally left the "Shadows" option off in the V-Ray settings...

Attached is the result with correct shadows.



Best regards,
Vlado

[Shimakaze]

That's why this thread is so interesting. To be perfectly honest, the matte/shadow stuff is very confusing for me, because it seems that people are using it in very different ways and want different things from it... no-one bothers to explain very well what they need.

Well since you asked...
I have always wished there was better ways to composit reflections. Pretty much no matter what you do, the reflection pass is always the final image, and even if you set an object as a matte object for reflections it still doesn't affect alpha contribution. Furthermore reflected objects don't work with multimattelements or similar either, and you can't break down the reflection into individual passes to composit that way. The workarounds are doable, but time consuming, and require a lot passes. This is probably too much to ask, and I'm not even sure if it's doable, but I really wish there was a way to control reflections better.
For instance, using Zdepth and velocity passes in post breaks down when you have reflective objects since they don't show up in the passes.

[LudvikKoutny]

Ok, so could i get a step by step explanation how to set it up correctly, pretty please?

I also assume i will need recent daily build for this, correct?

[LudvikKoutny]

And maybe to ease the confusion around it, i will try to summarize what i would expect from Matte/Shadow solution.

- A simple straightforward material that does not anyhow alter information of projected map (be it backplate or spherical map), so no diffuse or any other shading, just constant color, but one that can darken itself by catched shadows.

- Capable tool to project backplate or environment map on the surface of shadow catching geometry, so that objects look like they are standing on the surface, not floating in the air catching random shadow underneath.

- Correct reflection catcher that does not just add reflection color. It replaces the information that's on the backplate. I believe Vray already does it, but i may be wrong.

- It should not reflect environment, because it is already reflecting itself in backplate once.

- When enabling matte shadow, it seems that something is done automatically (seems like whatever is visible through matte surface is getting projected on top, regardless of what material is). That may be wrong, as when you are compositing, you need to be able to have shadow catcher surface black, but have it's original projected backplate color visible in reflections. Enabling matte for reflections enables shadows in reflections, but in case of setting directly visible environment to black, matte in reflections also becomes black.

- General ability to compose it in post processing package so that result is 1:1 to rendered one.

[vlado]

- A simple straightforward material that does not anyhow alter information of projected map (be it backplate or spherical map), so no diffuse or any other shading, just constant color, but one that can darken itself by catched shadows.

What about GI? How do you expect it to fit into the whole thing? This includes occlusion and color bleeding from/to the matte/shadow object onto/from non-matte geometry.

- When enabling matte shadow, it seems that something is done automatically (seems like whatever is visible through matte surface is getting projected on top, regardless of what material is). That may be wrong, as when you are compositing, you need to be able to have shadow catcher surface black, but have it's original projected backplate color visible in reflections. Enabling matte for reflections enables shadows in reflections, but in case of setting directly visible environment to black, matte in reflections also becomes black.

No, it's not wrong, but there needs to be an option to either have a separate "matte" background (which would be black or something else), or to render the mattes as black when directly visible, but as normal in reflections. Not sure about refraction/transparency?

- General ability to compose it in post processing package so that result is 1:1 to rendered one.

Your compositing package would need to support colored alpha.

Best regards,
Vlado