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Larry_g1s
05-01-2009, 12:58 PM
I'm trying to get the shadow only from the image attached. I've tried some of the suggestions from this thread here: http://www.newtek.com/forums/showthread.php?t=26997, but to no avail. I'm trying to use this for a t-shirt where it can placed on different color shirts. So the shadow needs to be separated from the ground plane. Any ideas.

Eagle66
05-01-2009, 01:12 PM
buffersave is from year 2005 and only for LW 6. :hey:

Larry_g1s
05-01-2009, 01:21 PM
buffersave is from year 2005 and only for LW 6. :hey:Right...which is why I started this thread for some solutions. lol

SteveH
05-02-2009, 07:13 AM
Can you use the Photoshop PSD Export function and only check the shadow button? I just tried it and although I had to invert the layer in photoshop - it did seem to do the trick. It's in the processing>image filter pulldown.

toby
05-02-2009, 09:22 AM
Radiosity shadows are not like raytraced shadows, it really is an absence of light, which can't really be a buffer, so none of the buffer savers will work. You'll just have to render the ground separately with the character hidden.

joelaff
05-06-2009, 04:39 PM
Right. Render the ground with the character set to unseen by camera (object properties Render tab). Adjust the diffuse values of the ground until you get a nice full range on the shadow. Then you can bring this into your compositor and put a curve on it to get the shadow looking the way you want it. Ideally you then use this as a matte to drive a color correction (since shadows are rarely colorless)

You can make something similar to this with am ambient occlusion node set in the luminance channel. May render faster than radiosity... (may not)

toby
06-22-2009, 02:21 AM
Radiosity shadows are not like raytraced shadows, it really is an absence of light, which can't really be a buffer, so none of the buffer savers will work.
That's just silly, I know better than that. This is what I used to think before I learned how radiosity works. Of course it can be a buffer, they just haven't made it accessible to us. But it might be possible with nodes.

daforum
06-22-2009, 03:17 AM
Make a ground plane (if you haven't got one already)

In the Surface Editor make it 100% transparent, the shadow density "Alpha"

In the Objects Properties make the geometry "Unseen By Camera"

toby
06-22-2009, 03:44 AM
Make a ground plane (if you haven't got one already)

In the Surface Editor make it 100% transparent, the shadow density "Alpha"

In the Objects Properties make the geometry "Unseen By Camera"
That only works with shadow maps or raytrace shadows, not radiosity or Ambient Occlusion.

But speaking of AO, you *could* plug an AO node into the transparency of the groundplane, and make the groundplane black. That would give you a shadow with alpha in the same render as your character. That's less-than-professional though, the shadow pass should really be multiplied over the ground, not dropped on top of it with an alpha.

gerardstrada
06-22-2009, 07:51 PM
One thing we need to keep in mind is that a shadow provided by GI is not a shadow properly, it's a shade. In Lightwave (and most common 3D packages), only lights generate shadows; shades provided by GI aren't interpreted as shadows; so if we are lighting a scene only with BG images, gradients or Backdrops, we can't extract those shades from a shadow buffer.

There are several ways to get those shades, btw. Before the nodal system, we needed to render separate passes and compose them by using:

the differential rendering technique
http://www.free3dtutorials.com/lighting/lightwave/how-to-compose-shadows.php

Today, with DP Filter Node Editors, we can solve all this in a single rendering pass and compose it within Image Filter NE.

But if you don't want to compose this within LW and just get the RO pass, we can isolate that pass with DP Filter Node Editors too:

http://www.spinquad.com/forums/showpost.php?p=212442&postcount=12

If you are looking for a way to solve this in Surface NE (supposing we don't have shadows or we have already separated shadows from radiosity shading), we subtract from a diffuse model (white color) with radiosity enabled, same model with radiosity disabled.

To adjust the strength of the shading we can input this result to a gradient or to a BoxStep node. The BoxStep node works like a levels filter in a compositing package (to set up the white and black points) and with a Gradient we can even tint the shading with other hue.

This output can be connected later to Alpha input of the Mixer tool to define the way a colored shading is mixed with a 100% luminous image texture for a LSD setup.



Gerardo

nickdigital
06-22-2009, 08:35 PM
If it's just a still you're going to use for a t-shirt you could just draw it in photoshop.

littlewaves
06-24-2009, 11:24 AM
I guess Larry found a solution by now but being as this thread has been resurrected anyway here's my two cents:

duplicate robot object

in the first one select "unseen by camera" in render tab of object properties

in copied version make it a matte object and set matte colour to white

toby
06-24-2009, 03:44 PM
I guess Larry found a solution by now but being as this thread has been resurrected anyway here's my two cents:

duplicate robot object

in the first one select "unseen by camera" in render tab of object properties

in copied version make it a matte object and set matte colour to white
What's that for?

littlewaves
06-24-2009, 04:01 PM
What's that for?

what my whole post or just the bit about the matte object?

toby
06-24-2009, 04:16 PM
The whole post
Cropping out a shape in the shadow doesn't sound like a good idea, and I don't see why you need a robot unseen by camera, the matte object can cast shadows

littlewaves
06-24-2009, 04:20 PM
I think I probably misunderstood what he was asking for.

I thought he was just trying to get the shadows on the ground plane and nothing else so he could layer up different elements in a limited no. of inks for t-shirt printing.

Anyway the reason for the matte object is to remove the robot from the image so he can be superimposed back in different colours.

Sekhar
06-24-2009, 06:06 PM
Actually, can't you just make the floor surface and environment white? That'll give you a luminance mask. Unless I misunderstood... E.g., see below.

Tobian
06-24-2009, 07:22 PM
Yeah the simplest method would be to make a white-only radiosity pass, but that would mostly only give you occlusion...

As it happens, I was advising about this elsehwere http://www.spinquad.com/forums/showthread.php?p=250740&posted=1#post250740

You could do either as I have done, or just make feed the node group into luminosity.

The only downside with this technique is I haven't figured out how to separate the diffuse element from the shadow element, so you have to clamp out the diffuse shading, which means, if you change the light, you may have to tweak the gradient to match...

Anyway if it's for stills, it's not an issue, and to get 'just' his shadow, make him 'unseen by camera' - transparency will not work, as that fades the shadow too, just make him invisible to the camera, and not rays, and he'll still cast his shadow.

Tobian
06-24-2009, 07:43 PM
With the teapot 'unseen by camera' it looks like this...

If you reverse the scene, telling the object to be seen by camera, and the ground plane to be unseen by camera, then you will generate a 'figure' only version, as well as a clipping mask for the object, and something to trim the shadow with, should you need too...