Am 19.10.2016 um 07:13 schrieb omniverse:

> Seeing this I began trying to find out if the File_Gamma=srgb I just began using
> recently was making a difference from File_Gamma=2.2 I had been using prior to
> that.
> 
> Well, that wasn't the thing that caused me a tremendous surprise because I was
> only seeing a real change if using assumed_gamma=1 for global_settings instead
> of srgb I also started using for that. A brightened image, as expected, which is
> why I had trouble with the idea of the necessity of adding it to all my scene
> files the many years ago now.

This is to be expected /if/ you were using PNG output.

Most image file formats require that the generating software encodes the
image data to match the viewing system's gamma. This is what is known as
"gamma pre-correction". If the generating software encodes for a
different gamma, the viewing system will display the image differently.

The PNG file format, on the other hand, allows the generating software
to choose an encoding gamma independently, and store the chosen gamma in
the file header; it is then up to the viewing system to read that gamma
information, and decode the data accordingly. Provided the decoding
software supports this mode of operation, it can therefore properly
display the image data in the same manner no matter the encoding gamma.


> By using Antialias_Gamma=1 in my povray.ini the rendering I was testing all this
> with went from over a minute (plus 3 to 10 seconds) to only 20 seconds!!!
> 
> I put 2 of those images together or overlayed, one with and one without that
> option, applied as differences between them and it didn't show anything. No
> differences visible.
> 
> So I must ask, is that to be expected?

I'm a bit surprised about the magnitude, but I consider it possible, as
changing "Antialias_Gamma" also changes the effective anti-aliasing
threshold, though the effect also depends on the absolute brightness of
the colours.

However, with the symptoms observed you should be able to get about the
same speedup in render times by choosing a higher anti-aliasing
threshold, also without loss of quality.

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