Layout
- ShadowBlend
Layout
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The ShadowBlend plug-in is one of the more advanced
and useful features of RealiTools, but is also one of the easiest to use.
It's a Surface Shader, and can be found listed as RealiTools_ShadowBlend.
Quite often a job calls for the addition of LightWave-rendered elements
into real-life scenes, either still or video. This is by no means
easy. Just matching the lighting on your objects can take quite a
while. However, when it comes time for your object to cast shadows
on the background plate, you're just plain out of luck! The most
common way to do this is to use an
object that matches the background, put a front-projection image map on
that, and have your CGI object cast shadows onto it. However, there's
a problem with that. To match the background, the luminosity of that
surface needs to be 100%. But, to get nice dark shadows, the diffuse
of the surface needs to be turned up, too. If you put them both to
100%, your object will be way too bright. The only alternative so
far has been to play with the luminosity and diffuse until you get some
sort of workable balance.
Now, RealiTools ShadowBlend
plug-in does the dirty work for you. To use it, you make an object
to match the background just like you used to, you put the front-projection
map on it just like before, but now you also turn on ShadowBlend.
In many cases, you don't even need to set the options. But here's
what they do:
Matching Light Intensity is a value that
should be the total of all the lights pointed at the surface. Say
you had two lights, one at 25% and one at 50%, that lit your object just
like you wanted it. (Assume also that they both face the surface
that's receiving the shadow...) You'd set the Matching Light Intensity
to 75%. This way, if you need less light than 100%, you can still
have the surface match the background, and if you need more, you
don't have to worry about washing out your shadows. It's important
to note here that the plug-in will never let you "over-light" a surface.
No matter how much light you throw at it, the surface will never get brighter
than the background. In effect, you are telling the plug-in "Any
place that gets this much light should match the background, and anything
less is a shadow."
Minimum Shadow Brightness lets you set the
darkest the shadows will ever get. In real life, shadows are almost
never 100% pure dark. Changing this will make the shadows darker
or brighter.
Shadow Color lets you add color to your shadows.
The easiest way to find what your shadow color should be is to bring the
background image into something like Photoshop and use the eyedropper in
the darkest shadow you can find. Then, set the shadow color to that
value. Shadows are usually less than 20 in R, G, and B channels.
However, if you feel like making your composite happen in an alternate
universe, you can make the shadows any color you want (even pure white)!
Tutorial
Here's a simple demonstration of how to use ShadowBlend
to merge some CGI objects with a photograph.
1. Open Layout and load backyard.tga.
Make it the background image, and set the Layout background to display
the BG image.
2. In the Camera panel, set the custom size to 640 by 360 pixels,
and set the zoom factor to 4.0, to match the camera the photograph was
taken with.
3. Load grass.lwo,
table.lwo, and (if you
want), tablecloth.lwo.
4. Size grass.lwo so that it will be large enough that any shadows
cast by the table will fall on it.
5. Using the background image for reference, position the table about
where you'd expect to see it in real life.
6. Open the Surfaces panel, and switch to the "Grass" surface.
Activate the RealiTools_ShadowBlend plug-in.
7. Using the eyedropper in Photoshop, measure the color of some of
the other shadows in the scene. The darkest are colored about 2,
25, 30 RGB.
8. Open the Options panel for ShadowBlend, and set the Shadow
Color to 2, 25, 30. Set the Minimum Shadow Brightness
to about 8.
9. Rotate the single distant light in the scene so that it approximates
the position of the sun (about 60 degrees pitch, coming from the right
of the screen).
10. Turn on Trace Shadows in the Render panel, and press
F9 to watch ShadowBlend work its magic! Here's
the scene I came up with.
