Difference between “embed profile” and “tag”

[paulbk]

It’s still not clear to me. What is the difference between “embed profile” and “tag” an image?
Is there a difference?
Plain English reasonable interpretations might be:

A) Embed profile ? -- The entire color space profile is “embedded” in the image file. That is, the image file contains the embedded profile, such as Adobe1998, sRBG, etc.. This increases the image file size accordingly. But the advantage is, if the host display is color management savvy, it can use the embedded profile and does not need the profile to already exist on the host machine.  (yes..?? no..??)

B) Tag an image ? -- This sounds like only the name of the profile is provided within the image, not the entire profile as described in (A) above for embed. (I’m almost certain this is wrong.) Therefore, the host display must have access to the “named” profile. In Windows XP profiles are usually kept here: C:\WINDOWS\system32\spool\drivers\color.

A helpful answer addresses the question in the context of A & B above. And does not point me to yet another paper full of color speak dogma where a color priest is required to understand its message.

I’m an engineer (nuclear). In engineering most terms have precise definitions, usually according to an industry standard, such as, ASME, IEEE, etc.. I’m sure the color management world also have precise definitions for terms. My problem is I don’t speak “color management.”

p

[allan67]

Hello,

Adobe gives the following on one of the support pages:

"Most digital cameras attach the sRGB EXIF color space tag to JPEG files, but they don't embed a color profile in the JPEG file. Because the camera doesn't embed a profile in the JPEG file, Photoshop reads the EXIF data and opens the JPEG file into the sRGB color space."

and on a different page:

"You can embed ICC profiles into any of the following RGB, CMYK, or grayscale files saved from Photoshop 6.0 or later: .psd, .eps, .tif, .jpg, .pct, or .pdf. An embedded profile remains with the file, so the device's color space information can then be read by any ICC-aware application."

So your assumptions were totally correct:
embedding - ICC profile is included in the file
tagging - ICC profile name is included only in the EXIF tag and if application is not EXIF aware, this information is lost.

Allan

[32BT]

As a nuclear engineer you'll probably understand it depends entirely on the context. When I have a "melt-down", I simply "crash" and hit the hay. When you have one...

However, your description of A is indeed the common interpretation.

The interpretation of B is less specific. In normal use it generally refers to the act of assigning an existing profile to image data. If you subsequently save the image data to a file, then you can opt to include the profile assigned previously.

[digitaldog]

Embedding and Tagging are the same thing.

[paulbk]

re: “Embedding and Tagging are the same thing.”

That’s what I thought. Embedding and Tagging can mean whatever you want them to mean. Good thing you guys aren’t building bridges.

If I 'Assign' a profile in photoshop, is it tagged? If I DO NOT embed the profile when I save the file, is it still tagged? ..... I think not. All embedded files are tagged, but all tagged files are not embedded. In fact, tagged can mean whatever you want it to mean.

The best way to ask the question is more objective and deterministic:
C) How would you know that a file is tagged by examining the file in a hex-editor? What data structure are you looking for?
D) How would you know that a file containes an embeded profile by examining the file in a hex-editor? What data structure are you looking for?

If the answer to -C- is the same as the answer to -D-, then, there is no difference. If the answers are not the same, then, embedding is not the same as tagging.
----------
From the definitions below, “tagging” can mean embedded, assigned, or simply tagged in the EXIF data fields.

Real World Color Management -- by Bruce Fraser, et al
Glossary, pg. 552: tagging a document -- “The act of associating a source profile with an object. You can tag an object either by assigning a profile inside an application or embedding a profile in the object as you save it to a file.”

Side Bar, pg. 282:  Tagging is simply a generic term for the act of associating a source profile with an object or document. A tagged document is one that has a source profile permanently associated with it, as an embedded profile or an assigned profile. An untagged document is one that lacks a source profile.

[DiaAzul]

Embedding and Tagging are the same thing.
[a href=\"index.php?act=findpost&pid=62412\"][{POST_SNAPBACK}][/a]

I would beg to disagree on that. Taking the Adbobe quotes above and my own experience a file can be tagged with an ICC profile (i.e. stating which profile should be applied to the image) without embedding the ICC profile (the tables and data) in the image.

An image can be both tagged and have the ICC data embedded within it (through a pointer to the data or whatever mechanism defined by the file type). In which case the software may (a) read the tag, ignore the embeded data in favour of some alternate profile source, ( use the embedded data if the software is able to read it.

Therefore, files may come in three forms:
(i) Untagged, with no embedded data. Typically assumed to be sRGB files.
(ii) Tagged, with no embedded ICC profile. Assumes that end user has a copy of the profile.
(iii) Tagged, with embedded ICC profile. Assumption that end user does not have a copy of the profile.

To answer PaulBK's questions - The 'tag' is in the EXIF data, the embedded profile is in a separate container in the Tiff file structure. The data structures are clearly and explicitly defined for each case (apologies that I don't have time to dig up specific references at the moment).

[digitaldog]

I would beg to disagree on that. Taking the Adbobe quotes above and my own experience a file can be tagged with an ICC profile (i.e. stating which profile should be applied to the image) without embedding the ICC profile (the tables and data) in the image.

An image can be both tagged and have the ICC data embedded within it (through a pointer to the data or whatever mechanism defined by the file type). In which case the software may (a) read the tag, ignore the embeded data in favour of some alternate profile source, ( use the embedded data if the software is able to read it.

Therefore, files may come in three forms:
(i) Untagged, with no embedded data. Typically assumed to be sRGB files.
(ii) Tagged, with no embedded ICC profile. Assumes that end user has a copy of the profile.
(iii) Tagged, with embedded ICC profile. Assumption that end user does not have a copy of the profile.
[a href=\"index.php?act=findpost&pid=62438\"][{POST_SNAPBACK}][/a]

1. Why would an untagged file assumed to be sRGB? In fact, on the Mac, all untagged files are assumed to be in Monitor RGB in applications like Preview, Safari etc. An untagged file is simply RGB or CMYK mystery meat.

2. A file is either tagged or not. The profile is either embedded or it's not. At least with an ICC profile. Some digital cameras use EXIF data based upon DCF to define the color space from the camera (version 1.0 is either sRGB or "none" meaning if you set the camera to Adobe RGB (1998), you get silly EXIF data that says "none" which isn't at all helpful).

You can't tag a file and not have an embedded profile expect in scenario #2 above which is only applicable from some DSLRs that follow the older 1.0 spec of DCF.

[digitaldog]

From CMS for Photographers. Page 168-169:

EXIF Data and the Lie about Your Color Space: For whatever reason, when a consortium
of Japanese camera manufacturers came up with a method of identifying the RGB color space
of their camera data using EXIF data, they did so in an obscure and confusing way. In 1999,
the Japanese digital camera industry implemented a “standard format”they called Design Rule
for Camera File Systems version 1.0,or DCF for short.In that specification,the EXIF data simply
specified whether the camera data was encoded into sRGB based on the matrix setting con-
figured on the camera. If a camera encoded the data to Adobe RGB (1998) or any other avail-
able color space besides sRGB,the EXIF tag was set to “none,”causing Photoshop to produce
a Missing Profilewarning dialog if the color settings were configured to warn the user. This
caused all kinds of problems,to the degree that Adobe had to produce a plug-in for Photoshop
7 (and a setting in the general preferences for Photoshop CS as well as CS2) called Ignore EXIF
profile tag(see Fig. 5-4). This sets Photoshop to ignore the color space specified in the EXIF
data and the result is a Missing Profilewarning dialog,which allows the user to pick the correct
profile to assign. In late 2003, DCF 2.0 was introduced and it does specify Adobe RGB (1998)
in the EXIF data. Not all new cameras necessarily support this, however. None of this has any
effect on RAW data although it still does apply when a camera is set to shoot RAW+JPEG files.
The bottom line is you need to know what EXIF data is being saved in your camera files if you
don’t capture and use RAW files.If you set the camera for a specific color matrix for a processed
JPEG (or similar file),you will need to assign the correct profile upon opening the document in
Photoshop.
----

An ICC profile is different (and better) and can either be embeed/tagged or not. There's no middle ground here.

[bruce fraser]

Back when I wrote the paragraph quoted, EXIF was so weak and so badly supported that it didn't seem worthwhile making the distinction between an image whose color space was defined by the EXIF tag (it could either be sRGB or not-sRGB), particularly when many cameras set to shoot in Adobe RGB embedded the Adobe RGB profile but set the EXIF tag to sRGB, necessitating a special Photoshop preference to ignore the EXIF tag.

I did point out that tagging (assigning a profile) could be done without then embedding the profile on save, but saving without an embedded profile would create an untagged file.

"Tagging" and "assigning a profile" have basically been synonymous since the beginning of color management. If you want to undertake the effort to reserve the term "tagging" for the act the camera does when it writes the EXIF data to indicate sRGB, Adobe RGB, or Mystery RGB (those are the only possibilities in the current EXIF spec), I wouldn't want to argue the point, but expect a lot of misunderstandings in the process.

Personally, I feel that the EXIF tag is so limited (sRGB, Adobe RGB, or all other possible RGBs) that we shouldn't treat it as part of a color management system, but this is not a hill worth dying on.

[bjanes]

re: “Embedding and Tagging are the same thing.”

That’s what I thought. Embedding and Tagging can mean whatever you want them to mean. Good thing you guys aren’t building bridges.

If I 'Assign' a profile in photoshop, is it tagged? If I DO NOT embed the profile when I save the file, is it still tagged? ..... I think not. All embedded files are tagged, but all tagged files are not embedded. In fact, tagged can mean whatever you want it to mean.

The best way to ask the question is more objective and deterministic:
C) How would you know that a file is tagged by examining the file in a hex-editor? What data structure are you looking for?
D) How would you know that a file containes an embeded profile by examining the file in a hex-editor? What data structure are you looking for?

If the answer to -C- is the same as the answer to -D-, then, there is no difference. If the answers are not the same, then, embedding is not the same as tagging.
----------
From the definitions below, “tagging” can mean embedded, assigned, or simply tagged in the EXIF data fields.

Real World Color Management -- by Bruce Fraser, et al
Glossary, pg. 552: tagging a document -- “The act of associating a source profile with an object. You can tag an object either by assigning a profile inside an application or embedding a profile in the object as you save it to a file.”

Side Bar, pg. 282:  Tagging is simply a generic term for the act of associating a source profile with an object or document. A tagged document is one that has a source profile permanently associated with it, as an embedded profile or an assigned profile. An untagged document is one that lacks a source profile.
[a href=\"index.php?act=findpost&pid=62422\"][{POST_SNAPBACK}][/a]

Paul,

Thought provoking questions. As you probably know, there are two types of ICC profiles: matrix and table based. The matrix tables take up only about 550 bytes, and whether they are tagged embedded makes little difference with a normal sized digital camera file. The table based profiles, usually for output devices such as printers, contain extensive look-up tables and can become quite large. For example, the Drycreek.com profile for my local Costco (Noritsu digital printer) is 1.4M. If you are uploading jpegs for printing, you would not want to embed these profiles.

With these profiles, you can easily determine if they are tagged or embedded merely by looking at the file size.