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View Full Version : Rendering a models self shadows only


jonmalexander
04-09-2003, 12:01 AM
How does one render just the self shadows of an object? I know how to render just the shadows projected by an object, but I would like to just render the shadows that are created on a surface by the particular light setup I have. There is only one object in my scene. If anyone knows how I can do this, please help me out! Thanks!

--J

Kalimol
04-09-2003, 02:41 AM
Could you render a mask image with flatshading, then render the scene with the object turned off, then render scene with the object and composite them?

binder3d
04-09-2003, 03:33 AM
How would you do all the above Kalimol? Thanks.
:D

jonmalexander
04-09-2003, 06:35 AM
Yeah, I'd like to to know exactly what you mean, cause I'm not sure if it will produce what I am trying to.

Basically I am trying to do my own version of what was a cgtalk challenge a little while back. I am tryin to do an earthquake shot. And so I front projected a plane model that I have a pose slider that cracks the plane open like a fault line cracking open during an earthquake. Anyways, since it is a front projection map, I had to turn the ambiance up all the way on my ground model, thus there are no shadows. I want to do another render with just the shadows so I can overlay them in after effects.

Here is a screen grab from my shot, to give a better idea. Again, any solutions would be very helpful! Thanks! Oh and yes, I am doing this in A:M of course.

jonmalexander
04-09-2003, 06:41 AM
Sorry, here is the pic, my bad:

http://www14.brinkster.com/jonmalexander/grab.jpg

jonmalexander
04-09-2003, 06:42 AM
Alright, since I don't know how to post a pic here, here is the address to it, sorry everyone(please copy and paste the url in a browser window):


http://www14.brinkster.com/jonmalexander/grab.jpg

Zaryin
04-09-2003, 08:01 PM
Please don't take this the wrong way, but -- nice crack! :)

binder3d
04-09-2003, 09:59 PM
Jon when I went to the link I got the following error--
HTTP1.1 STATUS 403 Remote Access to this object forbidden This file cannot be directly accessed from a remote site, but must be linked through the Brinkster Member's site.

Can you send another link?

Kalimol
04-10-2003, 01:32 AM
Yeah, disregad my previous post on this topic...it'd obviously only work for stills....

Jon when I went to the link I got the following error--
HTTP1.1 STATUS 403 Remote Access to this object forbidden This file cannot be directly accessed from a remote site, but must be linked through the Brinkster Member's site.

Can you send another link?

Since it's on Brinkster, you can't just click the link--you'll have to copy the link and paste it into your address bar.

jonmalexander
04-14-2003, 09:44 PM
I'm guessing this can't be done in A:M, or no one seems to know what I'm talking about. But, I gues you can't just do a shadow render pass, where only shadows of the entire scene are rendered out? Thats all I'm trying to do, and I can't seem to figure out how. :scream:

daft
04-16-2003, 08:05 AM
"How does one render just the self shadows of an object?"

I know what you mean. But, I donīt think you can do this in A:M. We just hope that Hash will implement rendering passes some day.

passes in maya
Rendering Passes (http://www.thegnomonworkshop.com/tutorials/passes_layers/passes_layers.html)

pequod
04-16-2003, 09:45 AM
I'm guessing this can't be done in A:M, or no one seems to know what I'm talking about.

Unfortunately, there's no button that you can just press, but you can render all your shadows separately, but it's long winded.

A method that I use I learnt from David Rogers. Turn all your decals values down to 0 or replace the objects in your scene with identical copies that have their decals removed.
Next, you have to make all the objects in the scene essentially flat shaded, the easiest way to achieve this is to create a very simple material effector, it's attributes should be just a diffuse white and a falloff of 0. Then plonk this effector into your choreography so that it covers everything and render this with shadows on. The resultant image should look like a greyscale picture.
Now, open this image, your 'shadow pass' render, in a program like Photoshop or After Effects and make it a layer. On another layer beneath, have a normal render of your scene that included decals but no material effector or shadows. Then finally, simply change the shadow pass layer's blending mode from normal to darken. I use Commotion so that I can work with targa sequences, this allows me to use this method for animation. I also use Commotion's paint tools to retouch the image, as well as applying other post production tweaks like blurring or colour tinting your shadows etc.

You can also use this process to render specular highlights or depth of field separately (using the fog feature), but it won't work for reflections. I hope this helps or at least gives you some ideas.

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