Casting Shadow without casting light
Scavenger
Posts: 2,674
I want to have basically a fake shadow in my scene...
I have the spotlight set up, and it sends the shadow where I want, but I'd prefer for the spotlight not to actually put light into the scene..
Is this possible?
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Kinda-sorta possible, but tedious. Essentially, the material settings of each item in your scene determine how/if it reacts to light -- if you change every single material zone of every single one of them (which the exception of the thing you want the shadow on) to 0% Diffuse and 100% Ambient (with the Ambient color set to 255 255 255, or at least something reasonably light), I think that'll do what you want.
Well, that wouldn't be how I'd want to go.
I've played with shadow catchers before....will they grab light as well as shadow?
(I was hoping to do everything in this picture in Daz..as a challenge..without compositing in PS, but if i has to, I has to).
If the light doesn't illuminate the non-shadowed areas how will you see the shadow? You could adjust the overall lighting, in DS or in post work, so that the total lighting was as before adding the spotlight but there'd still need to be a difference between the shadowed and unshadowed areas. Beth's method would let you do it in post, and adjust the opacity of the shadow layer, but it's still going to affect the lighting of the scene.
In Photoshop terms, a shadow is a darker shape with some level of opacity placed over an image.
I want that darker shape. I don't want the brightening made by the spotlight on the areas that aren't the darker shape. in those areas, I just want the light I'm already using.
Well, if you have the render with black shadow/white everything else, load it over the top of your real render, and ctrl-click the RGB channel to load it as a selection, invert the selection, then hide the layer, add a new adjustment layer (levels, say) which will take the selection as a mask you can selectively darken the shadow area.
Maybe this can help?
http://snowsultan.deviantart.com/art/Shadow-Only-Lights-in-Studio-325589206
You can use the shader mixer to create a light that subtracts shadows instead of lighting non-shadows.
Thanks SnowSultan & Millighost.
right now, I've found a good illumination level that gives me the shadow I want without the light changing things, but I'll go thru both of yoru ideas to learn more.
Select the light casting the shadow you want, go to create another light of the same type and tell it to copy the selected light. Select the new light and turn off shadow casting, then turn off limits on the intensity and set it to negative the original value. Easy, simple, and works with the basic lights. I used to use it all the time before we had the ability to change the strength of shadows.
Also.. if you're using a more advanced light just set the intensity to 1% and turn off limits on the shadow strength and crank it up to 1000%
Negative light...cool.
If you stick that in a physics based render engine, does the world explode?
No, you just best make sure that everything is nailed down, first...because it would get sucked past the event horizon in a hurry.
No, you just best make sure that everything is nailed down, first...because it would get sucked past the event horizon in a hurry.
I trust you have a script to ease this process. :D
The negative light trick works like a charm.