PDA

View Full Version : Shadow Catcher and IBL GI



tburbage
11-21-2015, 12:02 PM
Does anyone know whether a surface with Shadow Catcher Material should be able to catch shadows generated by an HDR image backdrop? I've been experimenting with a scene with an HDR set up as backdrop via TexturedEnvironment, and with a ground plane w/ Shadow Catcher applied. When using non-GI lighting (e.g. Area Light as key) shadows appear just as expected.

But when I turned off the traditional lighting and experimented with various GI settings (Backdrop, Monte Carlo, Final Gather, alternately tweaking other settings) reflections and general shading look great but no apparent shadows on the Shadow Catcher ground plane surface. I verified that the IBL is set up correctly to produce visible shadows where expected by temporarily disabling the Nodes on the ground plane surface and just using 100% Diffuse. This tells me my GI settings in general make sense. Tried F9 renders in case VPR has a limitation but don't think that is the issue.

The only difference in the setup which produced the two images attached was whether SC (Shadow Catcher) was enabled.

lertola2
11-21-2015, 02:40 PM
I am almost sure that shadow catcher only works with lights.

spherical
11-21-2015, 03:42 PM
The only difference in the setup which produced the two images attached was whether SC (Shadow Catcher) was enabled.

Ummmm, either I' totally missing what's going on or the difference between those two images is that the plane is there in one and not there in the other; thereby showing the Textured Environment background as a whole. Shadows cannot be cast onto Textured Environment, as it's not "there".

tburbage
11-22-2015, 01:38 AM
When you apply Shadow Catcher, only shadows and optionally reflections are visible on the surface...

lertola2 I suspect you are right about Shadow Catcher only working for direct illumination, so I added a Dome light pointed straight down, with mapping set to Backdrop. That DOES work.

Sensei
11-22-2015, 03:20 AM
When renderer has to calculate spot,
it's enumerating lights, one by one,
asking them what light samples they have.
Light sample has fields such as position of light, direction of light, and color coming from that direction.
Light can return 1 light sample (point,distant,spot) or multiple light samples (soft shadow lights, area, dome etc).
Renderer takes direction of light sample, reverse it, and ray-trace from spot world position in that direction.
If ray-tracing routine returns -1 or value smaller than distance between light sample world position and spot world position, it means there is no obstacles between light and calculated spot, and light is affecting spot full power.
And light color from light sample is used to calculate final influence.
If reverse, light does not affect spot. It's in darkness, shadow.
You can make your own lights in Node Editor. I showed how to do it in my video tutorials.
(let's forget about transparent and semi-transparent obstacles in this description)

GI doesn't have any light samples. Everything is source of light in GI. Every spot in scene.

Shadow Catcher is reacting only for presence or not presence of obstacle (-1 return value, or value smaller than distance between light sample world position and spot world position).

madno
11-22-2015, 05:27 AM
Out of curiosity,

is it possible to mimic a shadow catcher in a GI only scene?
E.g. if there is a surrounding sphere geometry pointing inwards with an hdr that acts as background, reflection and lighting but there are no LW iights and no LW backdrop.

gerry_g
11-22-2015, 07:03 AM
If you go look at HDRI Labs SIBL free plugin you will see it does just that – put two spheres into you scene, one a HDRI reflection map , the other a high res jpeg of the same image, a light source (a real physical light) to mach the HDRI light point of origin and a shadow catcher ground plane. Image based lighting can and often does include real lights too, go download it and give it a go


http://www.hdrlabs.com/sibl/archive.html

Kevbarnes
11-22-2015, 10:16 AM
HDRI Labs SIBL free plugin go download it and give it a go

I was just trying to test this myself - although I haven't used it in some time
but I'm getting an error when starting up Smart SIBL 2.2 (Latest version) - it hasn't been updated for some time

error Line 2282, invalid argument 2 type to parse()

On LW 11.6.3

? Has any one got the same error ? - have tried re-installing plug-in but get the same error

madno
11-23-2015, 12:12 AM
gerry_g,

tried already a sphere and a light. With a light I get the shadow catcher to catch shadows, but only from the light, not from the GI. The other problem is, that the shadow catcher does not "see" the sphere. That means if I don't set an LW background, the shadow catcher shows nothing (or better it shows the LW native background which is just black). So my understanding is, that this concept does not work at all.

Is it possible to make a normal material that only catches shadows, has roughnes and reflects other opjects, but is "transparent" to all other aspects (especially it should not be visible as a reflection on other objects)? Maybe with nodes?

131160

JohnMarchant
11-23-2015, 02:08 AM
I was just trying to test this myself - although I haven't used it in some time
but I'm getting an error when starting up Smart SIBL 2.2 (Latest version) - it hasn't been updated for some time

error Line 2282, invalid argument 2 type to parse()

On LW 11.6.3

? Has any one got the same error ? - have tried re-installing plug-in but get the same error

Its been broke since LW 11 i believe. I have the source for it given to me by Christian, he is not doing anything with it now and believes its not optimised for the latest LW versions.

Any coders out there are invited to have a go and update it. Ive passed it to a couple of people but no real updates yet. believe the problem has allot to do with directory structure of where
you put the IBL, HDR and Images.

gerry_g
11-23-2015, 03:31 AM
Latest version is •SMART_IBL_2.4b182• will need to dig through developer forums on site to find it though, this version works just fine in LW2015.3 in 64bit mode, and I know for sure I had a version (I think 2.4) running in LW 11.6.3, but yes the light and the light only is what catches the shadows that is why it is set up to replicate the point of illumination from the HDRI

perhaps this link – http://www.hdrlabs.com/cgi-bin/forum/YaBB.pl?num=1316465879

Kevbarnes
11-23-2015, 12:05 PM
believe the problem has allot to do with directory structure of where you put the IBL, HDR and Images.

Many thanks for the info - I'll check it out



Latest version is •SMART_IBL_2.4b182 http://www.hdrlabs.com/cgi-bin/forum/YaBB.pl?num=1316465879

Thanks Gerry_g - just downloaded 2.4 I'll test it out to

Cheers :beerchug: Kev

JohnMarchant
11-24-2015, 02:54 AM
Yes thanks Gerry-g.

tburbage
11-30-2015, 02:26 AM
Latest version is •SMART_IBL_2.4b182• will need to dig through developer forums on site to find it though, this version works just fine in LW2015.3 in 64bit mode, and I know for sure I had a version (I think 2.4) running in LW 11.6.3, but yes the light and the light only is what catches the shadows that is why it is set up to replicate the point of illumination from the HDRI

perhaps this link – http://www.hdrlabs.com/cgi-bin/forum/YaBB.pl?num=1316465879

Gerry, thanks for posting this reference. I had just re-installed the "official" version a few days ago, but have replaced with the "Beta" one. Have not had time to play with it yet though.

A few notes about Shadow Catcher. The "caught" shadows do contribute to both the Shadow render buffer, and to Alpha if you have the catcher object's surface is set to Unaffected by Surface or Surface Opacity, but interestingly not if set to Shadow Density.

In a pure GI context (not using Shadow Catcher) the Radiosity channel (Effects:Processing Compositing Buffer Export) does capture GI shading which includes "shadow" information.

gerry_g
11-30-2015, 07:42 AM
I believe the purpose of the shadow catcher is to place a ground shadow only in the scene where you intend using the ground plane of you BG image as opposed to real geometry for your render I don't think it captures anything else, see this thread for generating full shadow pass


http://forums.newtek.com/showthread.php?148639-Shadow-Passes-better-new-techniques-than-white-objects&highlight=sensei

gerardstrada
11-30-2015, 10:44 PM
Just in case, a way of adding colored bouncelight to sIBL shadowcatcher is this:

http://s4.postimg.org/ryayasxn1/bounce_setup.jpg



Gerardo

Otterman
12-04-2015, 04:56 AM
Gerardo

I can't see the attached image....anyone else? Could do with this info right about now

cheers

pinkmouse
12-04-2015, 05:14 AM
It was hosted externally, I'm sure he won't mind me adding it here:

131328

Otterman
12-04-2015, 07:28 AM
Cool I will experiment! Many thanks Pinkmouse.

gerardstrada
12-05-2015, 03:34 AM
Al, Thanks! :thumbsup:

Andrew, the BoxStep node is used like a way of wp/bp adjustment. The Begin parameter adjust the black point (positive values increases the blacks) and End parameter drives the white point (values below 1.0 increase the whites and values above 1.0 diminish it). Default settings for DP ColorBleed commonly provides good results.



Gerardo