New User Tips and Tricks
From LuxRender Wiki
Where do I start?
If you don't know where to start, then head over to the LuxRender Download page and grab a copy of LuxRender. Included in the download package should be a sample scene for you to render to get an idea of what LuxRender looks like and how it performs on your system.
Next grab the exporter for your favorite 3d modeling application. If you need help, have a question, or would like to share your latest work in progress then head over to the forums. For more immediate help you can try our IRC Channel or irc.freenode.net #luxrender.
Important Information about Scale
NOTE: It must be reiterated that LuxRender tries to simulate how light behaves in the real world. So, do yourself a favor and check your scale. As an example, 1 Blender unit = 1 meter, so your glass of water is actually 5 meters tall.
What render settings should I use?
Fast rendering on GPU cards
You could achieve order of magnitude (even x10 better) speeds by using GPU rendering on OpenCL, if you have proper hardware (e.g. good graphical card). To do this, you usually set Rendering mode to SLG Path OpenCL, as described in GPU. This page shows how to configure Blender+LuxRender+OpenCL GPU_in_blender.
The default and recommended render settings (unless you use GPU rendering which limits choices) are MLT (metropolis) + Bidir (Bidirectional Path Tracing). For general renders you will almost always use this combination. Metropolis is an intelligent and unbiased sampler.
Again metropolis + bidirectional is going to give the best results.
Generally metropolis + path but again metropolis + bidirectional will work very well here and might be faster so try both.
Renders with caustics
metropolis with a low largemutationprob and a high maxconsecrejects + bidirectional.
Highly specular scenes (glass, glossy, metal)
Higher depth/bounces (bidirectional or path) is better. However you start getting diminishing returns over 50-64. In other words it starts to slow down with too many bounces.
For animations a more predictable outcome is preferable to "intelligent" but sometimes unpredictable render times of the metropolis sampler. For this the lowdiscrepancy sampler is preferable. Generally, the bidirectional integrator will give the best if you want complete, accurate global illumination. However, you may find the distributedpath or path integrator with a low max depth setting to give faster results.
Either use metropolis + directlighting, or, ld/hilbert + exphotonmap with a low pixelsamples setting (1-4), fewer photons, and optionally no final gather.
With regards to fireflies, a new setting has been added for firefly rejection. This setting should be available in your exporter, but if it is not, you can add it manually to the scene file. This setting goes in the "Film" area of the .lxs file and shouldn't need to go over 10. In fact I found that even a setting of 1 produced great results. There is a speed hit but if your scene has fireflies in it, this is worth it.
|"integer outlierrejection_k" |
Are there any things I should know about material settings?
If you use GPU rendering, be aware some materials might be not implemented yet.
The most important thing to remember about material settings is to never use extreme RGB values i.e. over 0.8-0.9 or below 0.2-0.1 (0.9 and 0.1 are pushing the edge of the envelope). If your values are too high it can cause fireflies and are just not realistic. Values that are too low are not realistic either, but are not as much of a problem, but I don't believe that there is an object which reflects absolutely 0% of the light it receives. A piece of white office paper is roughly equivalent to 0.8 - 0.9 depending on who you ask ;). But even if you use 0.8 for paper you can adjust the tonemapping settings so it looks nice and white. For mattetranslucent the reflection and transmission parameters in each RGB column should not add up to more than 1. If you have a reflection value of 0.6 0.6 0.6, then your transmission value can not be higher than 0.4 0.4 0.4.
If you have glass in your scene and it looks black inside, first check your normals, then try increasing the max depth of your integrator (bidir/path), if you still have black areas it could be partially inside another mesh or just weird geometry.
Bump maps are relative. When creating a bump map, if you use 50% grey it will be neutral and have no effect on the bump. White is raised, and black is sunken by the chosen amount. If you start with a black background, you can never go "into" the mesh with the bump.
Are there any things I should know about mesh settings?
The default blender cube is 2 meters by 2 meters or 6 feet by 6 feet. When learning to model in blender I never paid any attention to that, I didn't need to. But when you realize that your glass of water is 5 meters tall (15 feet) you begin to rethink how you model. Personally, I just model it then scale it and apply the scale. So instead of 5 meters I would probably scale to 5 inches or 0.127 blender units tall. Google calculator is good for those who don't normally think in metric (http://www.google.com/search?q==5+inches+in+meters). Then apply the scale to the model.
If you end up with weird dark areas in your render, please check to make sure all of your normals are facing out in to the world.
Why do I get faceted shadows or black edges on glass objects?
In black you have the plain triangle used for the intersection, in blue you have the shading normals and the corresponding surface orientation, in green you have the smooth surface approximated by the triangle and its shading normals, in red you have the ray. As you can see, the ray is above the triangle and below the surface defined by the shading normal. This is inconsistent and prevents LuxRender from computing a sensible reflection or refraction. This is because with the smooth surface (in green), the ray would never have got that far.
The only way to reduce this kind of artifact is to increase the number of faces on the object.
Other sources of black edges - low poly on any glossy/reflective/etc
Same problem like with Glass objects, can happen with other glossy/reflective objects.
Too low poly count can make the edges black if they are marked as smooth shading. Fix would be, to either make shark edges sharp (in modeler, e.g. Blender) or to subdivide the model.