Ideas on dealing with non-planar complex surfaces (like people) where shadows are cast
Posted: 21 November 2022 02:32 PM   [ Ignore ]  
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I’ve got a live-action shot that I’ve incorporated a 3d monster into using C4D. One issue I have with this shot is that the shadow of the creature passes over the kid, but the shadow is set to cast on a flat plane (of which the kid is not), so obviously it is not correct (see attached render pic).

Given the monster is so much larger then the kid, the kid would be mostly in the monster’s shadow. My guess on best to handle this would be outside C4D and do it in AE. Rotoscope the kid, then change the brightness/HSB of the kid to approximate a dark shadow on the kid, and mask out the effect(s) from the ankles down where the monster shadow is not passing over so that those are still normally lit from the sun.

I don’t see how this could be done in C4D short of completely making a 3d model of the kid with shadow catcher material, but I’m open to ideas that may be different from what I mentioned above.

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Posted: 21 November 2022 03:31 PM   [ Ignore ]   [ # 1 ]  
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Hi yngvai,

When you take a look at the kids self shadow, then the Monster shadow is not correct. That would be my take on it. But you asked:

Either take an character and match-move it, or take a roto tools and do it in a color grading session. Darker and less saturated, use a few shapes, so you can move them more easily.

All the best


Hi yngvai,

The Monster shadow is incorrect when you look at the kid’s (self) shadow. That would be my take on it. But you asked so I assume the Monster shadow is independent of the sunlight:

Either take a character object from the Asset Bowser and match-move it, or take roto tools and do it in a color grading session. Darker and less saturated, use a few shapes to move them more easily.

All the best


P.S.:
An excellent book to learn this is

The Art and Technique of Matchmoving: Solutions for the VFX Artist [1st Edition]
by Erica Hornung (Author)
I enjoyed it a lot, and yes, it is already a little bit old, but nothing of human movements has changed since.

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Posted: 21 November 2022 04:15 PM   [ Ignore ]   [ # 2 ]  
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Thank you. I’ll likely use roto tools and do it in AE.

When you say the monster shadow isn’t correct, do you mean the darkness/tonality of it, or the direction of it?

I set up the sunlight direction using a figure and matched the angle/length of the shadow of the figure with the kid (see attachment) knowing the height of the figure and the length of the kid’s shadow relative to the kids height. I didn’t have an HDRI of the day so I couldn’t match sun location exactly but did have a google 360 photo so I knew the approximate sun location to the south.

I know the darkness/color tone of the monster shadow isn’t correct, which is something I’ve been fixing in AE with color correction.

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Posted: 21 November 2022 07:31 PM   [ Ignore ]   [ # 3 ]  
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Hi yngvai,

Thanks for asking; that shows me that you want to get the best out of your project. Wonderful.

First of all, everyone naturally knows shadows, but often our audience are people who never have “worked with lights”. With that, they can’t tell what is wrong, only that something in the image is off. That pulls the attention away from the content you like to show.

Shadow is a tricky thing, as is light. Shadows have (more often than not) light and color from bounces. Bounces can be from all kinds of things, even the moisture in the air (more a diffusor than a bounce, but a similar effect). Here it would undoubtedly be something from the sand, or as I would see it closer to the floor, it would be different in color on her leg.

Yes, you are close. A running child inside a new shadow (composite) has two main challenges. Typically an object inside a shadow does not produce an extra shadow, if it does, the light responsible must be readable in the scene, and it certainly has a different quality. This can be color, blurriness, or a gradient of all.

I hope I did not step on your toes with that (if so – sorry); I just wanted to push more that your work is sound. Shadows are only really 100% black when underexposed or artificial, IMHO.

I typically use shadow passes as a matte for an adjustment layer, speaking of Ae. There I lowered the brightness with it and changed the saturation and the color. After that, I might put some light/color back in.

HDRIs are often shot and sadly corrected to “something,” making them useless. HDRIs are a representation of the light dynamic and color dynamic, which is often not understood. Some people even use a gray card to neutralize those and kill at that moment the color values. Gray cards are only for the average 0.18 value there. And even then, that is only a starting point, as it must match the .018 in the scene. In your scene, I would expect a lot of blue in the colors, but the warm-toned sand will “eat” into that.

Take a still of that movie into photoshop and create a white layer with a round little hole in it. Your eyes will use that white to “see” the color of the kid’s shadow in the sand, on her leg and her cloth. Measure that. It will give you a lot of guidance.

I hope that helps. I know you have put a lot of effort already into your project, and I want that you have success with it.

If you like to dive deeper into that, one of the books I enjoyed a lot, and would recommend over other books about that theme:
Artists’ Master Series: Color and Light Paperback – April 5, 2022
by 3dtotal Publishing (Editor) [Page 112 and following pages] … but well, the whole book is important , IMHO.

Enjoy!

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Posted: 21 November 2022 07:57 PM   [ Ignore ]   [ # 4 ]  
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Thank you again for all your help. You’re not stepping on my toes at all…it’s all very helpful information.

You had mentioned rendering separate shadow passes and that’s in fact something I did for one shot where I had to match the monster’s shadows to the kids. I rendered a separate shadow pass then used color correction tools in AE to get the monster shadow as close to the kids as I could in terms of its tone (the kids shadows have a bluish hue to them, which is obviously due to how it reflects off the sand and other factors as you mentioned). I didn’t get it exact but I got pretty close. I’ve attached a still from the final composite shot from that.

Thanks again for all your pointers.

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Posted: 21 November 2022 08:14 PM   [ Ignore ]   [ # 5 ]  
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Yes, that looks already very good.

Thanks for sharing and for being so open-minded, yngvai!

I guess the actors in the clip had a lot of fun!

Cheers

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Dr. Sassi V. Sassmannshausen Ph.D.
Cinema 4D Mentor since 2004
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