In a recent newsgroup thread by Thomas, a sub-topic arose about 'ICC profiles'
in JPEG and PNG images that are posted to the internet-- essentially about
whether or not the images actually show up as visually intended. As this seems
to be a rather important topic (to say the least!), I thought it best to start a
separate thread about the questions and comments that were posted there.

Thomas's original thread, for reference...
http://news.povray.org/povray.binaries.images/thread/%3Cweb.5ab82726b126f8c9a47873e10%40news.povray.org%3E/

Ive wrote...
> And a general note to everybody who's posting images to theses
> newsgroups: please make sure your JPEG image contains a ICC profile.
> Since about 2 months Firefox and Thunderbird have full color management
> enabled by default. Chrome and Opera do the same since quite a while,
> [...]

And Clipka wrote...
> ...the W3C officially recommends sRGB for all web content, so that's what
> browsers should default to if an ICC profile is not embedded.
>
> Also, a lot of images posted here are rendered with POV-Ray, which
> currently does not embed an ICC profile. So to comply with your request,
> each and every image would have to be post-processed before posting,
> which I consider unreasonable.
> [...]

My own *current* understanding of JPEG images is that they do not include an ICC
profile (and never have?) And that the vast majority of general graphics apps do
not 'embed' any profile in them. Meaning, the image will show up 'more or less'
as intended by the person who made it... assuming the image was made in an app
that was working in either a gamma 2.2 or sRGB color/gamma space-- the two
genarally-accepted defaults.

As others mentioned in the previous thread, I likewise don't know how to embed a
specific ICC profile into a JPEG image, or if it is even necessary.

For PNG images (whether made in POV-Ray or elsewhere), my current understanding
is that they DO have an embedded ICC profile, created when the image was made.
That profile would generally be either gamma 2.2 or gamma sRGB, depending on the
particular app... which *should* match the display gamma of a
monitor/computer... or rather, the *intended* or expected display gamma.

One main question seems to be: Should JPEG images *have* an embedded ICC
profile? And if so, how is that done?

There are other questions about this situation that need discussing-- but I
don't yet know what to ask ;-) It's all quite complex and technical.

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