Am 26.04.2010 00:14, schrieb Kenneth:

> Yes, I do see the need for that. But as a practical matter, I wonder if there is
> a discernable visual difference between a .png file and one saved as a
> highest-quality .jpeg? (I suppose that's open to debate.) The real point being
> that .jpeg *is* a universal standard (lossy, of course); but more importantly,
> it has no embedded gamma (AFAIK!!)--which means that how it shows up in
> application X is basically the same as in app Y or app Z--regardless of how
> those apps deal with embedded gamma in an image.

What you forget about is that...

(1) JPEG having no gamma chunk means that it will indeed probably show 
identical in all apps on /your/ computer, but that doesn't mean it will 
look like that on /other/ computers.

(2) If your computer has a display gamma of 2.2, then specifying 
File_Gamma=2.2 will give you /exactly/ that same feature for PNG files: 
Applications that do recognize the gAMA chunks will display it ok 
because they know the gamma, and other applications will display it ok 
because the gamma happens to match your computer's display gamma. Plus, 
/good/ software on /other/ computers will display the image ok even if 
that computer has a nonstandard gamma.

(3) If /your/ computer has a nonstandard display gamma - say, 1.8 - then 
using PNG will give you /some/ chance that it will look the same on both 
your computer and other computers (depending on the quality of the 
software used), while with any other file format (except HDR formats) 
you are /guaranteed/ that it will look /different/.

 > I guess mt main worry is this:
> Not all of us have the *latest and greatest* versions of
> image-manipulation/viewing software, to view 'correct' .png images in. (My own
> version of Photoshop is quite outdated, for example, and AFAIK doesn't read
> embedded gamma correctly. And I'm even wondering about the latest version of
> Firefox!) I suppose that most/all up-to-date versions of software have addressed
> this issue--but that's just a guess. In the final analysis: Can we expect a .png
> image to show up correctly even in all 'modern' software? A .jpeg image
> eliminates that question (given it's image-quality shortcomings.)

Yes - if you have your display system set up to exhibit a total gamma of 
2.2 (or your system is uncalibrated, in which case you're likely to have 
a gamma /somewhere/ around 2.2), and use File_Gamma=2.2, then the 
chances that a PNG will look the same everywhere is /at least/ as big as 
that of a JPEG looking the same everywhere.

> Given *best practices* of course. :-P  If such a .png 'default' is made a part
> of POV-Ray, I can only hope that the documentation will make it clear as to what
> those best practices are. In the past, this situation has been a can of worms.

It was a can of worms indeed - because POV-Ray didn't do input image 
files properly until a few betas ago, making it literally impossible to 
set it up properly. Current default settings should get you a long way 
without you even noticing it (at least for new scenes; legacy scenes are 
a different issue, being necessarily as "broken" as the old versions of 
POV-Ray they were created for).

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