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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 version of Photoshop is quite outdated, for example, and AFAIK doesn't read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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> Hmm, I vote no. Sorry to be the one nay-sayer here. Given the past
> problems of
> different applications not reading the embedded gamma of .png images
> correctly,
> is this a good idea? Or am I missing something that I should know about?
>
> Is this idea based purely on image quality (.png vs. .jpeg, for example)?
I don't think the default file type should be one that uses lossy
compression. However, I agree that the gamma confusion makes PNG less than
ideal. I'm not sure there's a better format though.
- Slime
[ http://www.slimeland.com/ ]
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"Slime" <fak### [at] email address> wrote:
> > Hmm, I vote no. Sorry to be the one nay-sayer here. Given the past
> > problems of
> > different applications not reading the embedded gamma of .png images
> > correctly,
> > is this a good idea? Or am I missing something that I should know about?
> >
> > Is this idea based purely on image quality (.png vs. .jpeg, for example)?
>
> I don't think the default file type should be one that uses lossy
> compression. However, I agree that the gamma confusion makes PNG less than
> ideal. I'm not sure there's a better format though.
Not unless we want to get into the "business" of promoting one HDR format over
another, which... well, let's just say that standards wars probably aren't the
best usage of anyone's time here, with the possible exclusion of Warp. :-D
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clipka <ano### [at] anonymousorg> wrote:
> 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.
Good point. (Actually, I thought that a .png image would *showcase* these kinds
of discrepancies in an even worse way; but apparently not, which is good to
know.)
Ken
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clipka <ano### [at] anonymousorg> wrote:
> Am 25.04.2010 23:20, schrieb Alain:
> >> How about changing the default output file type for both Windows and
> >> Unix version to PNG?
> >
> > Why not for all versions?
>
> With me having not much of an idea about Macs anyway, I pass that
> question on to any Mac experts listening right now...
Probably not an expert, but everything I've used on the Mac can read/write all
the POV-Ray output filetypes (apart from HDR). I'd say your arguments hold for
the Mac platform as well as Win/Unix.
(oh, and I vote PNG too; not sure about Win7 but XP certainly had no clue what
to do with TGAs, and I object to BMP on moral and aesthetic grounds ;) JPEG is
out of the question for your stated reasons. 2 of my English pence :))
Bill
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Am 26.04.2010 10:20, schrieb Bill Pragnell:
> (oh, and I vote PNG too; not sure about Win7 but XP certainly had no clue what
> to do with TGAs, and I object to BMP on moral and aesthetic grounds ;) JPEG is
> out of the question for your stated reasons. 2 of my English pence :))
I think BMP (which is the current default for POV-Ray for Windows) has
also become a poor choice for technical reasons, as POV-Ray's
implementation can only write uncompressed BMPs, making it a major waste
of space without any gain. (It would of course be possible to implement
compressed BMP output, but then again, why bother when there are better
alternatives around nowadays.)
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> 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.)
FWIW I had a model of the golden gate bridge and the red vertical cables
never worked with JPEG.
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clipka <ano### [at] anonymousorg> wrote:
> (It would of course be possible to implement
> compressed BMP output, but then again, why bother when there are better
> alternatives around nowadays.)
Um...because it would be free of embedded gamma? ;-) (Sorry, I can't seem to let
this poor old horse die a peaceful death.) Actually, I didn't know that a
compressed BMP image was even possible.
In re-reading the posts here, I get the impression that one of the reasons for
choosing .png as a default is that it's a smaller file size (compared to BMP,
for example.) In the old days--when hard-drive memory was at more of a
premium--that would have been a legitimate argument. But it's an issue that has
far less importance now. (ALTHOUGH, for uploading onto the 'net, a compressed
image is preferable; no argument there. And .png might well be the right choice,
for the reasons given.)
I guess a basic question (or some further food for thought) would be this:
Should the choice of POV's default file type be 'driven' by the needs of the
'net? I would estimate that the ratio of my own POV images (between JPEG/PNG and
BMP) is less than 1%. In other words, I only compress an image when I have to.
No compelling reason to do otherwise.
Although I work on a Windows platform, I actually hadn't considered BMP as an
alternative to the PNG 'default' idea. (It's the POV default anyway, on that
platform.) But it does have one compelling virtue: The majority of computer
users work on Windows--and it's an easy step to convert BMP to JPEG (or PNG!) in
any image app--assuming that everyone who works with POV-Ray *has* another image
app to do that with. (Who doesn't??) Yet, I don't know how/if Macs work with BMP
images; I assume they can handle it.
But in the final analysis, I guess there's nothing wrong with PNG as the
default, if it's implemented and documented well.
Ken
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Slime <fak### [at] emailaddress> wrote:
> I don't think the default file type should be one that uses lossy
> compression.
I didn't know that POV-Ray even supported lossy formats as output...
--
- Warp
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On 04/25/2010 06:44 AM, clipka wrote:
> How about changing the default output file type for both Windows and
> Unix version to PNG?
I'm in favor of this as that's the most common format I use ... but that
doesn't make it correct. Everyone has made compelling pro and con
arguments, but I think it's rather like asking a painter what medium
they like to work with ... acrylics or oil. Personal choice right? If
something other than png is ultimately the choice ... no worries for me
as the format I like to use is just a command line option away!
Jim
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