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Am 28.05.2010 19:54, schrieb Jim Holsenback:
> Hola,
>
> Working on this section in docs:
>
http://wiki.povray.org/content/Documentation:Reference_Section_3.2#Adjusting_Radiosity
>
> and came across something I'm not quite clear on. In particular the
> "maximum_reuse" entry ... 3rd line into that entry refers to
> "reuse_count" setting ... typo? (lifted this from change-log)
>
> Also a general review of that section would be nice before I call this
> section done. So anyone who feels inclined to have a look, please do so.
> If you see anything else that needs attention, either mention it here
> ... or on the "talk" page for that section, and I'll follow up.
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always_sample
You can force POV-Ray to only use the data from the pretrace step and
not gather any new samples during the final radiosity pass. This may
reduce splotchiness. To do this, use always_sample off, by default it is
on. It can also be usefully when reusing previously saved radiosity data.
---------------------------
As a matter of fact, for high-quality results "always_sample off" is
virtually a /must/, and for quick renders it's a good thing as well.
(Expect this value's default to change accordingly before the release;
I'm even pondering removing that parameter altogether.)
---------------------------
brightness
The brightness keyword specifies a float value that is the degree to
which objects are brightened before being returned upwards to the rest
of the system. The default value is 1.0. In cases where you would raise
the global_settings{ambient_light value} to increase the over all
brightness in a non-radiosity scene, you can use brightness in a
radiosity scene.
---------------------------
This is actually not so good advice. In an ideal world, "brightness"
should be set to 1.0. If the overall brightness doesn't seem to fit, the
diffuse color of objects and/or the overall brightness of light sources
(including ambient>0 objects) should be adjusted.
A typical problem in radiosity scenes is that people set "pigment" to
e.g. "rgb <1.0,1.0,1.0> and "diffuse" to 1.0, and then tweak the light
source and "ambient_light" brightness to make the image look right. This
will not work in radiosity scenes, as it will give too strong
interreflections. While you /can/ compensate for this by reducing
radiosity "brightness", it's generally discouraged. Instead, in this
case the surface properties should be fixed (e.g. "diffuse" set to
something around 0.7, which is much more realistic).
An exception is the adjusting of "brightness" to compensate for low
"recursion_limit" settings: Setting "recursion_limit" to e.g. 1
effectively suppresses part of diffuse interreflection (those using more
diffuse bounces); to compensate for this, it is suggested to increase
"brightness" a bit (e.g. 1.2 instead of 1.0).
----------------------------
nearest_count
The nearest_count integer value is the minimum number of old ambient
values blended together to create a new interpolated value. The total
number blended will vary depending on error_bound. All previous values
that fit within the specified error_bound will be used in the average.
It will always be the n geometrically closest reusable points that get
used. If you go lower than 4, things can get pretty patchy. This can be
good for debugging, though. Must be no more than 20, since that is the
size of the array allocated. The default value is 5.
----------------------------
This sounds contradictory to me: Is the total number of blended samples
governed by error_bound, or will only the n geometrically closest
samples be used?
Fact is, there is no upper limit on the number of samples blended - all
available samples are blended that match the error_bound and
maximum_reuse settings. Nor is there any internal data structure these
days that would require nearest_count to be capped. (The "nearest_count"
parameter is still limited to 20, but this is just a relic which
probably hasn't been removed for the sole reason that values >20 are not
really very useful in practice.
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