Dave,
This is very interesting stuff. Like Mike, I would rather you didn't limit your explanations for fear of saying too much. We can take it!
I've always used Adobe up 'til now, but will switch to SRGB. 99% of my pictures never go near a print; they are only ever seen on a screen.
Thanks
John
On Fri, 4 Feb 2005 23:16:41 +1300, David Mann <[EMAIL PROTECTED]> wrote:
On Feb 4, 2005, at 1:31 PM, Rob Studdert wrote:
Neither sRGB or Adobe RGB are really good matches for ink print processes
however true colour photographic processes are pretty close in gamut to sRGB.
To expand on this point a bit, ink processes are CMYK (a subtractive process) while you might have guessed that the colour spaces mentioned above are RGB (an additive process).
When you overlay a CMYK gamut plot with an RGB gamut plot you end up with something resembling the Star of David: a large central area where the gamuts overlap, and a few smaller areas around the edges where they don't overlap.
This makes it very difficult to get the most out of your gear: the printer can't print some of the colours that the screen can display, and the screen can't display some of the colours that the printer can print!
The only way to totally encompass a CMYK gamut with an RGB one is to make the RGB gamut absolutely huge, but this causes problems of its own, relating to tradeoffs with bit-depth, file size and tonality. Colour spaces of this magnitude are available (EktaSpace RGB, Kodak Pro Photo RGB) but they are quite specialised and should be used with care.
BTW you can now buy printers that have a combination of CMYK and RGB inks. This complicates things a bit so I'll ignore those :) I'd actually be interested to see a true CMY monitor (an LCD would be perfect for this) but that'd be extremely difficult to implement with today's RGB-centric computer systems.
Having said all that you can argue numbers until you're blue (or magenta, if you like) in the face. I'm still very happy with my prints from sRGB files. sRGB is quite a safe option if you want to be sure that your printer is capable of reproducing nearly all of the colours represented in your file. And as a bonus the file is instantly suitable for the web without having to convert colour spaces.
I would actually hazard a guess that the content of most Adobe RGB-tagged files would fit within the sRGB colour space anyway. It's only the heavily saturated colours that would be clipped out, and most files aren't _that_ saturated. Low-saturation images (eg portraits) are theoretically better served by sRGB anyway, as there will be slightly better tonality (mainly in the green channel). This is the tradeoff - a small gamut gives better tonality at the expense of lower peak saturation, for a given bit-depth.
As an experiment you can try opening a file that was captured as Adobe RGB, then set up Photoshop to soft-proof with the sRGB profile as the output device. Then turn on the gamut warning feature. That will tell you whether or not your Adobe file fits within the sRGB colour space. Soft-proofing doesn't need to be activated for the gamut warning to work, but it tends to be automatically switched on after you set up the soft-proof options (this is why you might see the photo suddenly look brighter).
Feel free to use the Hue/Saturation tool to see how much saturation you can add before running into problems.
Cheers,
- Dave
http://www.digistar.com/~dmann/
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