Allan Brito has published a neat trick to simulate light groups with the GIMP. I don't think this is a YafaRay specific trick; it should work with the internal renderer as well.
Allan writes:
One of the most interesting features of LuxRender is the option to control light by groups. With this feature we can separate several light sources into groups, and change the intensity, temperature and turn them on and off during the render. It allows us to produce several different renderings from a single image, and save lots of render time. For instance, we can have in the same rendering lights representing daylight visualization and other lights for a night shot.
There are other tools that have similar options such as Maxwell Render and their Multilight feature, and even V-Ray and Mental Ray with the use of a MAXScript in 3ds Max. But, what if we could fake this effect using nothing more than GIMP or any other image editor? I was browsing through a SketchUp user forum this week when I found an interesting tutorial about the setup of a scene using SketchUp, Twilight Render and GIMP to fake this type of effect. Almost immediately I fired up Blender 3D and YafaRay to test it and the technique really works.
Link
8 Comments
Hello!
What a cool idea !
In fact now i think about it, you could do the same with nodes and renderlayers !
How cool is that ?
grtz wzzl
Actually, this technique was already demonstrated before by Daniel Martinez Lara:
http://www.daniel3d.com/pepeland/misc/3dstuff/ilum_normal/%5Bpepeland%5D-iluminating_with_normal_nodes.htm
The page contains a demo video, blend files, and it's possible to modify the direction of the lights as well.
http://www.graficaobscura.com/synth/index.html
@ijstaart: faking light using normal nodes is a different approach alltogether, combining renders of different light setups simulates lightgroups, much like the link above this post.
@wizzleteet: yes, this can be done with nodes, even changing the colours of the lights at the same time, Lighting BSoD has one page explaining it
http://wiki.blender.org/index.php/Doc:Tutorials/Lighting/BSoD/Adjusting_with_Nodes The tech is pretty old, Grafica Obscura doc says at least 1992.
by the way, I've dropped a couple of request of a solution to have this features INto blender:
http://www.blender.org/forum/viewtopic.php?t=15879
and
http://blenderartists.org/forum/showthread.php?t=168688
but it didn't arise much interest, and i can't understand why!
Wasn't this implied with many 3d tutorials? That is where I get it.
This is a good technique. Very good time saver, it took time to adjust light and then rerender, so make render for each light then composite them together.
@lsscpp: what you ask sounds pretty similar to creating a group composed of one (or more) light(s) and then a renderlayer with such lamp group. You can also override a renderlayer material, both things are there to allow tricks that need overriding all lights or materials with something else. http://en.wikibooks.org/wiki/Blender_3D:_Noob_to_Pro/Render_Settings#Output_.2F_Render_Layers "Light:" and "Mat:"