Re(3): use of sRGB as a default
Re(3): use of sRGB as a default
- Subject: Re(3): use of sRGB as a default
- From: Matt Deatherage <email@hidden>
- Date: Sun, 20 Jun 2004 12:30:24 -0500
On 6/20/04 at 8:58 AM, Andrew Rodney <email@hidden> wrote:
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The "experts" in this series of posts outside of Apple have thus far
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been asking for clarification FROM Apple just what is going on. We
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don't invent this stuff, we just try to figure out how it works and
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explain it.
Yeah, terminology works both ways. :)
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John tells us that untagged files in Panther are assumed to be
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displayed in the Generic RGB profile and yet for some reason, when I
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tag a file with that profile, it doesn't match
Time out. Per my previous message, this seems incredibly vague to me. Here's what I *think* you're saying:
| Untagged files in panther are assumed to be *created* in the Generic RGB
| *color space*, and yet for some reason, when I tag a file with a
| *Generic RGB source profile* and open it in Photoshop, it doesn't match
| what I see in Preview.
Am I close?
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and when I tag my
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display profile, it does match what I see in Preview verses
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Photoshop.
Again, I think you mean:
| ...and when I embed my display profile as a *source profile* in
| the image, Photoshop displays it just as Preview does.
This second part is more just clarification than terminology, but to someone like me, it makes all the difference. If I'm right about what you meant, then if I read the question the way I phrased it, I know how to try to reproduce it and what you're seeing. Otherwise it's too vague for me, and honestly, I'd skim over it unless it was a bug report that I had to address - in which case I'd write back and ask for clarification.
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As Bruce pointed out, this is a bad idea (assuming the display
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profile). At least by assuming sRGB, the user can "fix" the image or
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do whatever is necessary and even if the document remains untagged,
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the next user in the chain will also assume the same color space
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(sRGB).
John has made clear, at least in my mind, that this line of thinking is not good for Mac OS X. Why? "Even if the document remains untagged" is an unacceptable answer - there should be no such thing as untagged images. As a programmer, what I want to know is what I'm supposed to do if I find one.
Look, most programs aren't Photoshop or Fireworks, and saving an image file is a check-off item at best. If someone can explain in simple terms what to do with untagged images, as in what profile to embed, almost all programs will do it once the word gets out. If you offer the option of "even if the document remains untagged," though, a programmer who has one day to spend on image file writing routines will read that and say, "Oh, so I pass the buck on to other programs" and leave it at that. Code you don't write never needs debugging.
If you want Preview-like programs from small developers to do the right thing with profiles, it needs to be clear and simple what the right thing is. Sample code is best, but a few bullet point instructions will do. If the answer comes back with "Photoshop 5.5" and "AdobeRGB" and "if it stays untagged," they're going to punt.
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The display profile should only be used for preview purposes
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along with the assumed or known embedded profile. That's why this
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Generic verses display profile behavior discussed above is so
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confusing and frustrating.
Well, it's one reason. :)
As I said to Olaf, this sounds like a simple rule: "Display profiles are never source profiles, only destination profiles. Do not embed display profiles in image files." Is this *ever* false? If it's always true, perhaps someone should request that ColorSync add the concept of destination-only profiles and return errors when trying to embed one in an image. Errors get programmers' attention.
Actually, programmers *love* errors if they lead to a simple fix, like a documentation page that says, "This error code means you're trying to use a destination-only profile as a source profile in an image. You're probably trying to embed a display profile in an image when you meant to embed the source color space profile. If you're _sure_ you want to embed this profile, clear the destination-only flag and try again."
(I'm talking out of my hat here; it's been over a decade since I was in the DTS group that answered ColorSync questions, and even then, I didn't answer them, but I hope the point is clear - if there really are simple rules, let's get the OS to help enforce them.)
I didn't mean to turn the list into a novel or tech weblog about this, and I probably won't be replying much for the next couple of weeks. But my frustration on reading has become as high as some of you writing these messages, and I'd started to say something several different times and stopped. I really, truly feel that if everyone can settle on precise terminology, and then explain simply what most programs should do with color profiles, then most programmers will go along with it.
Sample code would be even better. There's ColorSync sample code showing how to _display_ an image with an embedded profile, but it's all the theoretical stuff that allows or requires you to choose printer, display, proof, and RGB profiles, and how the matching is performed, and all that, and your average screen capture program *won't do that.* You guy aren't complaining about a lack of tools to apply profiles to image files; you're complaining that most programs don't treat the embedded profiles consistently, and I'm quite sure that's because most programmers have no idea what to do in the simple, default cases.
Tell programmers what to do and for the most part they'll do it, if they understand what you're asking. Advanced stuff is different, but honest to God, if you can make default rules for embedding profiles in JPEG files that had none embedded, and give those rules to the Bryce team, I'll bet you a box of Krispy Kremes that they'll implement them.
Then you can figure out what Web browsers should do. :)
--Matt
--
Matt Deatherage <email@hidden> <
http://www.macjournals.com>
I read this list in digest mode; copy me privately for faster responses
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