Am 26.09.2018 um 18:04 schrieb Warren:

> I take what you say into account , but I must let you know some things :
> First, I learned the two pass method with this site : http://www.nolights.de
> 
> And In my main scene file (pov file) I have those lines (I put comments to be as
> accurate as possible, that wasn't the case in my precedent post, I apologize.

Two things I'm noticing about your radiosity settings:

(1) You're turning off the pre-trace almost entirely in your main pass.
That does indeed avoid doing any double work.

(2) Aside from the pretrace settings, the radiosity settings are
identical, with the exception of `error_bound`. You should be able to
achieve the same effect - both quality- and speed-wise - by setting
`low_error_factor` to the ratio of the two values, and using just one
pass with full pretrace.


> -------------------------
> I remember some years ago, I rendered the well known scene of Gilles Tran :
> 'glass' in WIndows 7 in one pass , and with a count of 200 , that took me about
> 6 days in 1280x1024 or so and then in two pass in Ubuntu 16.04 with this time a
> value of count of 400 with the same resolution of 1280x1024 and the same other
> radiosity values that took me 5 or 6 hours for the first pass and less than 10
> hours for the second pass (I'm sure it took  one day at most for the two pass
> renders , and compared with the six days in one pass...).

A different OS makes me wonder whether different hardware was also
involved, and maybe also different versions of POV-Ray. The Ubuntu 16.04
render can't have been much more than 2 years ago, Windows 7 might have
been as much as 9 years ago.

> Now I just wonder if your answer is the same with those informations. :-D.

In general, yes. I can think of a ton of things that may have played a
role - including the possibility that by applying your approach you
might have inadvertently compromised the radiosity quality, or
inadvertently cut short an excessive pre-trace.

I might make some controlled experiments to verify your claims, but for
now I stick to my current understanding of the inner workings of the
radiosity algorithm, according to which there should be no such effect
that couldn't be achieved by other means.


(There /is/ another approach to improve performance via a separate
radiosity pass, which is to replace some complex objects in the scene
with faster-rendering stand-ins; but it comes with its own pitfalls, and
the same effect should be achievable by making use of the `no_radiosity`
and related keywords.)

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