View Full Version : Total 'Front Projection Mapping' Frustration

01-04-2011, 11:56 PM
Hi guys.

I am having a real hard time with this front projection mapping process. I looked in the help files for a long time to find this solution to having a simple plane mesh catch the shadows of an object but basically be invisible in the scene. The problem is that it still has diffues/specularity settings applied to it so it looks a lot darker than the same image being used for the background. What if I have animated lights and camera movements?

Am really having a hard time with this one, the help file has images of an alien casting shadows on a road, which is the exact result im looking for but having little sucess reaching.

Wouldnt it be hard to adjust the diffuse/luminosity for every frame so that the plane matches the background exactly?

Sorry for the length of the post, hopefully _someone_ can help me.


01-04-2011, 11:59 PM
Have you tried the steps in this thread?

Mr Rid
01-05-2011, 02:45 AM
I dont think the matchmoving thread solves the problem. LW wont render only a recevied shadow while the mesh stays invisible as it sounds like you want. In a separate render, you can save out shadows only in an alpha by setting surface alphas to Shadow Density. Then you have to composite the shadows back into your RGB render using After Effects, etc.

I recall there's a shadow catcher plugin that allows you to render only a received shadow in the RGB render... I cant find what or where now... I thought was on the hdrlabs site... anyone?

But these things dont work for radiosity shadows, which I had an odd workaround for- http://www.newtek.com/forums/showpost.php?p=897557&postcount=12

01-05-2011, 03:13 AM
at the hdrlabs.com you can download sibl. When you run sibl, it also creates a ground object that has a node setup to catch shadows: where it has a shadow it is opaque, no shadow = transparent. you can try to use this node setup in your objects.

01-05-2011, 01:50 PM
Thank you for the replies,

I will try that method though I wish there was a simpler way of doing it. Am sure back in the day when I worked for a company that used another 3D program (wont name it) it could do this effect the way a person would expect it to work.

anyway, thanks again and ill keep moving ahead.:)

01-12-2011, 01:21 PM
On your ground plane surface set alpha channel to shadow density in the advanced tab. Then you can render out files with an alpha that includes your object and it's shadow. Comp that onto your BG ground plate.

01-12-2011, 05:08 PM
Worley's G2 plug-in is supposed to be able to take care of that. http://worley.com/E/Products/g2/composite.html

Of course, there are cheaper ways to handle it.

01-21-2011, 09:33 AM
max has its matte/shadow material, modo has its shadowcatcher, we lightwavers have no easy way of doing it, a least not with a few clicks. Hopefully CORE will help with this issue.
BTW, cant seem to find sibl... is it Sibl Edit? Sibl GUI? SamrtIBL?

01-21-2011, 10:58 AM

download the lightwave one, download some sibl set (from here http://www.hdrlabs.com/sibl/archive.html).

run the script, it will create several objects, one is a ground object. This one has a node setup to catch shadows.

01-21-2011, 04:28 PM
attached is a screeny of the ENTIRE sIBL shadowcatcher node setup.

This seems 'WAYYYYyyyyy too simple to work-- can someone explain to me how it does its magic??? tnx 8~

01-21-2011, 04:46 PM
well, I'm not a node expert but I guess that the lambert shader will 'shade' your geometry with shadows and then this is transformed into a color and the color into a scalar for the transparency. So...in the object where we have a shadow for the lambert shader this is black, no shadow is white. White means that the object is transparent and black means its opaque. so where you have a shadow it is opaque and where you don't have a shadow it is transparent, thus showing the background plate. pretty simple hey? the best ideas are always simple.

01-24-2011, 11:54 AM
tnx Zardoz, I'll give it a try :thumbsup:

02-07-2011, 03:42 PM
I've tried this, but can't get it to work as I'd expect.

When I say expect, I never actually would expect this nodal setup to work, but it is almost there... but how can I set it to work perfectly? What steps do I need to take with the light exclusions etc?

Mr Rid
02-07-2011, 05:00 PM
I do a lot of integration with live action and it has always been preferable to isolate the shadows cast into the plate with a separate 'shadow density' pass to better control in comp.

I run into a bigger problem where I need an object to receive/cast a shadow from/on another object but not receive/cast from/on other objects.

02-07-2011, 05:04 PM
Cheers Mr Rid, I do normally do this, but was trying to do some very quick tests this evening and wanted a 'quick and dirty' shadow catcher... this does do the trick after some tweaking, but you can't have your objects penetrate the ground at all, otherwise the object will (rather obviously) show through the ground plane.

I much prefer doing a shadow pass, but sometimes being able to crank the shadows out with the ground is nice and quick!

07-15-2011, 05:02 PM
heya, glad you like my shadow catcher nodes. Indeed, it is almost too simple to work. During testing I had it setup with more than 10 nodes, and then eliminated and condensed it into what I thought was the simplest solution.

It is NOT perfect, can't be, because it's auto-generated and has no idea of what your scene/lighting looks like. It's meant as a starting point. If you select a node, you'll see Notes in the commentline of what may need fine-tuning. Typically, you would play with the Contrast and Brightness in the ColorTool node, until the lit areas of your shadowcatcher are fully transparent and the shadow itself has an appropriate density.

And yes, it's a cheap trick. The Lambert Node is used to sample raytraced shadows PLUS contact shadow from radiosity. These will turn out differently depending on your scene, that's why it gets tweaked with the ColorTool. The result is piped into the transparency of the ground. This Node obviously requires Raytracing and Transparency to be turned on.

Oh, and yes - in real production you would always render out a separate shadow pass. This shadowcatcher setup is for quickies and animatics.