What does the percentage complete in a render mean?

Drogo Nazhur

I have had images run for over a thousand iterations and show 0% complete. Conversely, I've had images run for a hundred or two iterations and be 100% complete. 

Also, I have had images that were only a little bit complete and they looked more finished than images that were almost all complete.

So what does the percentage complete in a render telling us?

nemesis10

Oh, to avoid a long complicated answer, think of ray tracing.  Imagine a simple scene with a room, a box, a light, and a camera. When you look at the scene, you see the box as the light bounces off the box and enters your eye. In 3d rendering, the opposite is true.  The computer starts with the theoretical light beam starting from the box and traces it back to the camera and repeats again with another light beam on and on until it reaches a state where the pattern of light and darkness is statistically above noise (convergence).  In my simple scene, the calculations are relatively easy so the iteration number will be small and the image will be very crisp and sharp very fast. Now image a much more complicated scene with lots of lights, diffuse light, translucence, hair with millions of reflections and suddenly we aren't talking millions of calculations, we are talking tens of billions of calculations and may never reach convergence.  So basically, the percentage complete tells you how close the image is statistically approaching a state above background noise.  A proviso should be made that human eyes and brains do a great job of filling things in so a pointillist painting may look coherent to our eyes but statistically a mess to a computer so "finished" is in the eye of the beholder.

felis

It tells procentage of pixels that have converged (reached their end value), given the Rendering Quality there is set, and relative to the Rendering Converged Ratio (i.e. if Rendering Converged Ratio is 95%, the render will be 100% when the render reaches 95%.

You can find these values in Render Settings > Progressive Rendering.

Richard Haseltine

felis said:

It tells procentage of pixels that have converged (reached their end value), given the Rendering Quality there is set, and relative to the Rendering Converged Ratio (i.e. if Rendering Converged Ratio is 95%, the render will be 100% when the render reaches 95%.

You can find these values in Render Settings > Progressive Rendering.

The key points to bear in mind are that the percentage is or a percentage (when done it is 100% of 95% converged, for example) and that it isn't a value that steadily ticks up from 0 to 100% - some areas converge quickly and some slowly, for example eye are often a sticking point (or frelections and refractions generally) while dark., matt surfaces often finish quickly.