[argyllcms] Re: Could someone help me understand something applying printer profiles.
- From: "Alastair M. Robinson" <profiling@xxxxxxxxxxxxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Fri, 25 Jan 2008 04:23:39 +0000
Hi :)
Leonard Evens wrote:
Thank you. I did figure that out myself. Using cctiff helped understand
the process better, so when I went back today to look at photoprint, it
became clear what to do.
Yes, having done conversions manually makes it much easier to understand
what's going on "behind the curtain" doesn't it? Definitely an area
that needs documentation.
I'm still not sure what Image>Set color profile is for. When I
> set something there, and the original file had an embedded profile,
it warns
me it will override it. I don't know what the purpose of the before and
after is. And how does all this interact with the default image profile
set under options?
Image->Set Colour Profile makes the image behave as though the profile
you select were embedded in the image. That's why there's a warning if
you're over-riding an embedded profile. It's mainly useful if you have,
say, a scanned image and a profile for the scanner, or maybe one or two
odd images in AdobeRGB when you use sRGB as a default profile, and these
images don't have the correct profile embedded.
I thought it might be something like that. So, is it true that I can't
do essentially the same thing with cctiff or lcms's tifficc? Do they
perform calculations in lower precision?
No, not really - the "problem" is merely that the tifficc / GIMP
workflow involves quantizing the data to 8 bits before sending it to the
printer driver. PhotoPrint avoids that.
If I have it right, then the comment that I was losing information was
not quite accurate.
Well, the information you're losing is just low-order bits. Whether
that's a problem is entirely your call ;)
It would be more accurate to say I was processing
the information at lower precision. It would be the difference between
adding rounded off floating point numbers or adding first at higher
precision and rounding off afterwards.
Yes, that's a pretty good analogy.
I think I understand that sort of thing pretty well as a mathematician,
> and I see that it could make a difference, but I would be surprised if
> the difference were significant compared to all the other variation
present
> in real life color management and color editing.
Whether you'd see any real difference would depend a lot on how
well-behaved your printer is. Generally, though, any difference would
be subtle - you might see a little contouring in a sky or something like
that.
All the best,
--
Alastair M. Robinson
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