Iray Progressive Rendering documentation

josh.pactor

Any chance we can get this page completed?  http://docs.daz3d.com/doku.php/public/software/dazstudio/4/referenceguide/interface/panes/render_settings/engine/nvidia_iray/progressive_render/start

Barring that, is there somewhere else that these settings are fully explained?  I'm most interested in finding out the effects of Max Samples, Max Time, Rendering Quality, and Rendering Converged Ratio (apart from just "bigger values improve quality", though hey, that works too).

Thanks!

mjc1016

Max time, samples and converged ratio are the three main controls for length of render.  If the max time (2 hrs default) is reached before the samples or converged ratio are reached, the render will be 'finished'.     Same for samples.  And of course, if it converges quickly (long before 2 hrs) it will end the render, too.

Rendering Quality is a bit differnet...it's similar to 3Delight's Shading Rate option...it's an overall 'quality' control but is constrained by the other controls.

josh.pactor

Thanks!

nicstt

You can also change the settings during render; can be useful.

 

hphoenix

From my understanding (please, anyone who knows if or how I might be wrong, illuminate us!):

 

"Max Samples" is the number of iterations/passes through the beam tracing algorithm.  Each pass refines the image.  You'll see these counting up in the render progress window.  Each pass (after the first) refines the image a little more.

"Max Time" is simply a limit on how long to keep refining the image.  It puts an upper limit on how long to keep rendering the image.

"Rendering Quality" is simply how close any pixel has to be to its prior sampled value before it is considered 'converged'.  The higher this value, the closer in value any pixel has to be to its prior value before it is considered 'converged'

"Rendering Converged Ratio" is what percentage of pixels have to be 'converged' (to within the value specified by rendering quality) for the image to be considered 'complete'.

If ANY ONE of "Max Samples", "Max Time", or "Rendering Converged Ratio" are reached or exceeded during a pass, the image is considered 'complete', and the render passes stop.

Setting "Max Time" (and also I think, "Max Samples") to zero will cause that stopping condition to be ignored....so with Max Time of zero, it will continue to render until one of the other conditions is met.  Time won't be limited.

 

For test renders, "Max Time" should be kept low, say 300s (5 minutes.)  Max Samples can be set to 500, Rendering Quality at 1 (or even less) and a Convergence ratio of 75%.  This will result with a grainy image with speckling, but the general appearance of the rendering and lighting should be apparent very quickly.

 

For final renders, "Max Time" should be zero, Max Samples should be a large value (at least 5000, probably 10000 to 15000 for good quality), and Rendering Quality set to 2 or 3 with a Convergence Ratio of 98% or 99%.  I recommend avoiding a Convergence Ratio of 100%, as this can be unachievable in some renders (where a given pixel keeps swapping back and forth between two values, but both are outside the range set by the Rendering Quality.)  At 99%, that means 1 out of every 100 pixels is still outside the rendering quality level.....so for larger renders, to avoid graininess one must set the convergence ratio higher (but still try to stay below 100%).

 

Also, remember that lighting and camera parameters affect the image quality a LOT.  Choosing the right film speed, shutter speed, exposure levels and light intensities/colors/etc. can make a huge difference.  Lower speed film requires longer exposure (slower shutter speed), but for scenes with animation, will result in much more significant motion blur.  Higher speed film will reduce that, but requires a faster shutter speed.

Tobor

Samples and time are simply "stop-at" values. They DO NOT control final rendering quality. All they do is programmatically stop Iray from rendering indefinitely. Your render can, and often does, look perfectly good before these stop-values are reached. (Exception: time when you're on a slow-rendering machine. Two hours isn't long for a complex scene and CPU-only renders.)

Convergence ratio as a quality metric is an *estimate*. There is no mechanism in Iray that knows when a pixel looks good. All it can do is compare the value of ray hits to a given pixel, and when a certain percentage of these hits provide the same result, it says "I'm done." But here, things get complicated, because Iray appears to also base at least some of its convergence ratio math on nearest-neighbor comparisons. A scene with metal flakes or other textural or procedural noise will take longer to render, because it's harder to compare nearby pixels to determine accuracy in the rendering.

Rendering Quality is a threshold for judging convergence. It's not a stop-at value, but setting it higher or lower changes how picky Iray is in judging the variance of ray hit values.

People put WAY too much emphasis on these settings. Your own eyes are better than Iray in judging render quality.These stop-at render settings are really made for programmatic renders and animation, where a human isn't involved in making a judgment of "finished."