Jay Smith wrote:
> In various places (not necessarily in this thread) there is discussion
> of "embedding profiles" and "tagging with color space".  It is NOT clear
> to me if these are two phrases with the same meaning.

In general they are the same thing. Some people have schemes
to tag a file with a symbolic profile or URL, but these
schemes are less robust (it needs to be a "well known" space
or you need net access to interpret the colorspace). An
embedded ICC profile is an unambiguous way of tagging it.

>>From my reading, especially of  G. Ballard of www.gballard.net
> http://www.gballard.net/psd/go_live_page_profile/embeddedJPEGprofiles.html
> http://www.gballard.net/psd/save_for_web_embed_ICC_profile.html
> Ballard is emphatic that images for web use should *NOT* have "embedded
> profiles" and should *NOT* be "tagged with a color space" except under
> unusual circumstances.

Lots of people have lots of opinions. Serious color people often call
untagged raster files "mystery meat" though, and shake their heads.

> His demonstrations are worth a look.  (However, I wish his writing was
> more precise and less repetitive.)

His website is a bit hard to follow.

A lot of his advice is along the lines of "it's not fully supported
so it doesn't work so don't use it", but of course this is chicken
and egg stuff. He's busy pushing sRGB, while others are railing
against the loss of quality of having everything squashed though sRGB!
[Note that his rant about Apple is largely moot now, since they
  have switched to Gamma 2.2 and assuming un-tagged = sRGB with OS X 10.6 ]

The bottom line is that it depends on your purpose. If you
have a particular reason to specify device dependent colors,
then you deliberately don't want to tag the file with a profile.
You may be working around limitations of other elements (for instance,
say a plugin like flash doesn't honour embedded profiles, and
you want to match an image to certain colors displayed by the plugin),
but if you want to convey actual color, then tagging the image
with the colorspace (or using a device independent color representation
like L*a*b*) is the right way to do it. If you want maximum compatibility,
convert to and tag with sRGB. If you want minimal loss of gamut and
don't care about compatibility with non-color managed applications,
you might choose some other colorspace.

Note that in an age of very wide gamut displays, even things like GUI
elements need color managing, if the GUI isn't going to look accidentally
garish, and that un-tagged images may look kind of ridiculous if
the (even color managed application) assumes that un-tagged images
are the output device space.

> QUOTING G. Ballard
> ICC profiles from 99 percent of the digital photos he publishes, mostly
> because adding color profiles increases file sizes, about 4K per photo.

Hmm. I'm not sure that 3k for an image is really that significant
given the bloat and slowdown on typical websites due to flash,
advertising re-direction, Web 2.0 etc. etc.
Even the small images on his website are 35k, so 3k for an sRGB profile
is about 8% - hardly noticeable. The moves to use URL references is
one aimed at reducing the overhead, but I wonder if it is worth the
trouble and breakage it will cause.

Graeme Gill.

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