Shadow catcher/matte problem

[MaverickMongoose]

Hi there,

Im trying to get a perfect reflection with shadow with an infinite background (either by domelight gradient or image as back-drop in dome light).

I've tried the shadow catcher and the newer matte option in the RS Object tag, but the floor (a disk) is always visible and the reflection always looks weird.

Any idea where I went wrong or if theres a better way to do this?

I was hoping to do it with the matte catcher because the attenuation feature is quite helpful as well.

Here's the project with my tests https://we.tl/t-jGd9dUM6r5

Thanks for your help!

[Dr. Sassi]

Hi MaverickMongoose,

I'm always open to diving into something, even if it defeats physical rules. If it expands an artist's expression, I will provide my take on it. Let's have a look.

Just from my observations, you can't have both. If it is 100% reflective (Perfect reflection, as mentioned, which no object on the planet has), you will see no light on the surface and, with that, no shadow.
If you can see the light, there is something that does not reflect the light (Imperfect reflection); that difference would show where the shadow is.

For whatever reason you like to have it, render passes and composite those. I'm curious how the shadow will limit the reflections, even in an otherwise impossible combination.

If the background shines through, you will get only a partial reflection, except more tangential; it will be a fresnel reflection, but no background "floor" anymore. I hope that makes clear what you see in the images below.

An endless "floor' that carries the information of the backplate will show up the moment it reflects the "Background," as that would add to the light. At that moment, it couldn't be the same anymore.
Please add your HDRI back in.
CV4_2023_drs_23_RSsr_01.c4d

In other words, find a balance, and decide what is essential and what location.

One idea to showcase this, swap out the materials, "Metalness" vs. Standard Material. What sometimes appears as a shadow is a refection of a shadow.
CV4_2023_drs_23_RSsr_11.c4d

Cheers

[MaverickMongoose]

Thanks Sassi, they do look a bit unnatural dont they. I wonder if its possible to achieve by just excluding lights and objects over in the PROJECT tab of the light. I'll keep experimenting

[Dr. Sassi]

Hi Maverick-Mongoose,

We have seen so many impossible things, and most of the time, we have not seen them other than on a screen: Large explosions in space, or any explosion for that matter; who has seen a factory go up in a big bang? We have a distorted vocabulary of what is real or not, and yet, many art directors might have a clear about those things; otherwise, we wouldn't enjoy them on the big silver screen, at least I do since–ever. Even the dynamic range to film an explosion there, while having fine fire details, would be pretty impossible. But yet, "we" pay admission to see it for a few decades. So, a reflection-shadow mix should be possible in any way.

I would try to solve it somehow in Composting, certainly with 32bit/floating, to avoid the gamma-based problems of 8- or 16-bit comps.

I'm, as before, not convinced that it is possible without sacrificing one or the other quality. Aesthetically or physically.

Shadow can only be read as a contrast to light. As all metalness excludes shadows, shadow applied would require introducing the qualities that shadow does, darken, and desaturate.
100% reflective means it is as bright as the stuff that could be seen from the surface itself. So it must be darker than the shadow to not eat into the shadow.

The only way I could think of selling the 100% reflectivity while some kind of darkness is guiding the eye to read the set is to have the shadow on the object so the shadow reflects in the floor.

Good luck.

Cheers

[MaverickMongoose]

I got it working with some trickery in the reflective materials opacity channel, gives an infinite floor look from any angle. I think doing it in post is definitely a better option though;)

[Dr. Sassi]

Looks good to me, Maverick Mongoose, but you are the judge.

I received the initial post defining the reflection as perfect and 100% sharp. Sharp as in the same as the objects reflecting of itself.
Your image shows me; I f understand it now correctly; it can be softer.
The shadow is the reflection of the Object's self-shadow.

Yes, I believe that having all parts as layers allows for faster "fine-tuning" of the results.

Thanks for sharing your progress.

My best wishes for your project.

[MaverickMongoose]

Sorry, yeah it works with sharp reflections as well, just thought it looked better a little blury;)

[Dr. Sassi]

Got it; thank you for taking the time, MaverickMongoose.

Going by both images, the shadow is the object shadow, not a show on the floor. This would have led to a shorter reply above.
Nice to have it discussed in the forum from many angles; it is hopefully of use to someone.

Enjoy!