color profile embedding (not conversion) utility?

[John]

Hi John,

As for my understanding of "tagging", I always assumed that this was
simply an instruction to the editing software telling it to disregard
the embedded profile (or absence thereof), assume the file is in color
space X and assign that profile as the document working space, (i.e.
tag the file with that profile). No data conversion occurs, and the
file is saved with its original profile (or no profile). I welcome any
corrections or additions to this hypothesis.

Thanks again for your input.
Cheers,
Mike

Your hypothesis is sort of half correct. I think the word 'tag' is maybe a
source of confusion - better to use the word 'assign'. When you *assign* a
profile to a document, you are associating that profile with that document.
In other words, you are defining the calibration of the RGB data and making
it device independent. When you assign a profile to an image in Photoshop,
as you correctly observe, you override any existing profile with the new
one. In other words, the RGB data remains unchanged, but you are re-defining
the calibration of it.

As an example, suppose you have a file with sRGB embedded. If you *assign* a
wide gamut colour space to it (e.g.Wide Gamut RGB) you will note that the
colours become extremely saturated. This is because you have effectively
re-defined the definition of the RGB values to represent more saturated
colours.

What happens when you save off the file depends on your colour settings; if
you have 'Preserve Embedded Profiles' enabled, the assigned profile will be
embedded in your saved file. However, if you have 'Preserve Embedded
Profiles' disabled, the file will be saved off without an embedded profile,
so that when you open it subsequently, it will be 'untagged' (have no
assigned profile), and Photoshop will *assume* the current RGB working space
profile. (BTW, you can also choose to embed or not during a save via the
File|Save dialogue, irrespective of your colour management policy.)

Your working space profile is not affected by any embedded profiles in
individual documents. It remains as set by your colour settings. However,
working space only affects 'untagged' documents (i.e. documents without an
assigned profile). In such cases, the working space profile is *assumed* for
editing purposes, but will not be saved off in any files unless you
specifically instruct it to be.

The embedded or assigned profile will always override the working space
profile. You will see the colours according to the document's own profile
because Photoshop does an 'on the fly' conversion from the document colour
space to the monitor's colour space. The file data itself does not change,
as you are aware.

If you are taking Don's approach of hand crafting raw scan files, you will
be assuming your working space profile and colour corrrecting so that you
effectively end up with a valid file in that colour space, say Adobe RGB
(1998). It is therefore wise to embed this profile to your *edited* files
rather than leave them unembedded - this will ensure that you have the
correct profile on subsequent opening. However, leave your unedited raw
archive files unembedded.

 

[Don]

You can rest assured that
in NikonScan, if you select either ScannerRGB or turn off colour management
altogether, you will get native scanner RGB, or as Don likes to say
'Uncorrupted data'

LOL! Very good! ;o)

Don.

 

[Don]

There is a bit of confusion (at least on my part) about the meaning of
a "tagged image". Putting this aside for the moment, the meaning of
"embedded profile" is quite clear. To me, an embedded profile
describes the color space of its associated file. The file was either
created in that color space or subsequently converted (from whatever
color space it was in, e.g. raw scanner) into that color space. Thus
when I find that the file output by the scanner software has an
embedded profile (sRGB) it suggests that the "native" scanner data have
been converted into this color space before writing the file to disk.
That, of course, requires changing the data. [See my previous post to
John which describes my workflow and PS color settings.]

I think I better "tag" John, now... ;o)

You see, I only have Photoshop version 6 here so John's remarks are
much more appropriate. PS 6, for example, totally ignores EXIF data
and strips it all away when the file is saved (a major annoyance for
my digicam images!).

Having said that, I think a part of the problem is probably the
terminology as well, so let's settle for Photoshop terms.

Assign (or Tag as we have been calling it) simply means a marker is
saved with the file indicating the profile to be used but the image
data is not changed.

Assign and Convert, by contrast, means change the image data.

Finally, "Leave as is..." as Photoshop calls it means don't do
anything to the file; don't assign a profile and don't change the
data.

BTW, you can test all this out as follows. Take a scan without a
profile and import into Photoshop. Assuming your preferences are set
to "Ask" a dialog pops-up. Select "Leave as is..." and then save the
image as RAW. When you do that only image data is saved without any
prefix or suffix (which is where profiles, tags, EXIFs, etc live).

Close and open the same image again. This time select "Assign
working..." and again "Save as" using the RAW option.

Finally, close again and open but select the third option "Assign"
click the check mark for "convert". Again, save as RAW.

You can then compare these three files to see what action causes image
data to change. If you don't have a compare program, you can use "fc"
(file compare) in DOS. Type "fc /?" for parameters.

Your phrase "waiting for another PREVIEW scan" adds to my confusion.
As noted above, when I select "Redraw" the scanner performs another
preview scan.

It could have been the NikonScan version (I used both 3 and 4 over two
scanners LS-30 and LS-50) but I remember distinctly that in some cases
the image was just redrawn instantly without performing the new scan.

Anyway, I don't use NikonScan anymore, but if every time you press
Redraw the scanner does perform another preview scan then everything's
fine and just ignore what I said.

BTW, you probably know this, but an exclamation mark in a yellow
triangle indicates when the Analog Gain settings has been changed but
the display was not updated with a Redraw. This icon appears in the
information panel.

It is my understanding that when the image imported into PS was 16 bit,
the histogram display used all 16 bits. I am using PS CS(8). Please
correct me if I am wrong.

There are two issues here. One is that Photoshop's 16-bit mode is
actually 15-bit. At least for version 6. I'm not sure about version 8
but I believe that hasn't changed. Maybe someone else can jump in to
clarify this. If so then any histogram uses this reduced 15-bit image.

The second issue is more important, because the Photoshop histogram
display (at least in version 6, again) is only 8-bit i.e the data is
reduced to fit into 256 bins available in the display window.

Don.

 

[John]

I think I better "tag" John, now... ;o)

You see, I only have Photoshop version 6 here so John's remarks are
much more appropriate. PS 6, for example, totally ignores EXIF data
and strips it all away when the file is saved (a major annoyance for
my digicam images!).

Don.

Yes, it was when I upgraded to CS2 from Photoshop 6 that the problem with
the EXIF profile first reared its head - before that, images saved from
NikonScan with CM off came in untagged as they should. Desks were hammered,
expletives were uttered, then I worked out what was going on. What actually
pointed me in the right direction was the name of the sRGB profile - it
wasn't sRGB IEC61966-2.1 or Nikon sRGB - just plain sRGB. So I looked at the
EXIF data and there it was. I still don't understand why that profile is
there though - I assume that it's a default that doesn't get removed rather
than a deliberate insertion.

 

[Don]

On the chance you may have missed my reply to this message (#38) it is
just above in message #37, in my reply to John.

Hi Mike,

Yes, I did see it and answered it but my news server was on the blink
last night so I sent it out first thing this morning.

Anyway, looks like John solved that EXIF kink!

Many thanks for the link to the wide histogram. That is a vast
improvement. It's a pity that it doesn't function in real time
simultaneously with editing the image with the Levels adjustment. But
one shouldn't look a gift horse in the mouth.

I know, that would really be nice. The trouble is with huge 16-bit
files there's a lot of data so it takes a while to tabulate it all.

Don.

 

[Don]

Yes, it was when I upgraded to CS2 from Photoshop 6 that the problem with
the EXIF profile first reared its head - before that, images saved from
NikonScan with CM off came in untagged as they should.

That's very important! I saved the message and I made a mental note
for when I take the plunge and upgrade PS. It won't be until I get a
new computer, though.

Desks were hammered,
expletives were uttered, then I worked out what was going on.

In my case it's pulling of hair and climbing of walls but the end
result is the same. ;o)

What actually
pointed me in the right direction was the name of the sRGB profile - it
wasn't sRGB IEC61966-2.1 or Nikon sRGB - just plain sRGB. So I looked at the
EXIF data and there it was. I still don't understand why that profile is
there though - I assume that it's a default that doesn't get removed rather
than a deliberate insertion.

I think you're right. It's probably one of those "it will be
overwritten anyway because everybody will embed a profile".

Well, they sure didn't count on us contrarians, did they! ;o)

Don.