Hi,
99.9%, probably more, of the CRT displays available are using rec709
primaries. No matter Mac, Win, or whatever. Regarding gamma,
you will find a lot of variation, between 2.3 and 2.8.
It is wrongly believed that Macintosh computers use monitors whose
transfer function is different from the rest of the industry. The unconventional
QuickDraw handling of nonlinearity is the root of this misconception.
So, for CRT monitors, sRGB would be adequate in the vast majority of
cases. In the other hand, TFT and LCD displays behaves quite different.
The transfer function is not a exponential-like curve but something that
may be from an S-shaper curve to anything. Also, primaries are different.
Some TFT vendors are adding firmware to make TFT behave like CRD,
but there is still no agreed standard on that.
AdobeRGB is most used as exchange or working space. There is no
physical device that really renders in AdobeRGB, however, there are
very high-end softproofing devices for prepress that are *emulating*
AdobeRGB. But these are pretty rare.
The only point no so clear with sRGB is white point. D65 is used in many
color-critical environments, but the average monitor is probably set to
something higher, D91 or D93, which gives more bright at expense
of a blue cast. For a user that don't care about color accuracy, this
would be the best choice. Even so, D65 may yield a slight blue cast
when comparing against a proof in D50 box, so, for true softproofing
or match to screen, D50 should be used. But then the yellow cast is
so evident that makes the monitor unsuitable for anything but softproofing.
So my advice would be: use sRGB as default profile for CRT monitor,
and probably for TFT too. If you want extra precision, let enduser to
adjust gamma. Keep rec709 primaries. If you want to let enduser to
adjust whitepoint, that's ok, but hide it as "advanced calibration".
There is a function in lcms cmsCreateRGBProfile() that will let you to
create any of these spaces. Here is as example, how to clone AdobeRGB:
cmsHPROFILE CreateAdobe1998RGB(void)
{
LPGAMMATABLE Gamma[3];
cmsHPROFILE hProfile;
cmsCIExyY D65;
cmsCIExyYTRIPLE Primaries = {{0.64, 0.33, 1 },
{0.21, 0.71, 1 },
{0.15, 0.06, 1 }};
Gamma[0] = Gamma[1] = Gamma[2] = cmsBuildGamma(256, 2.2);
cmsWhitePointFromTemp(6504, &D65);
hProfile = cmsCreateRGBProfile(&D65, &Primaries, Gamma);
cmsFreeGamma(Gamma[0]);
cmsAddTag(hProfile, icSigDeviceMfgDescTag, "(lcms internal)");
cmsAddTag(hProfile, icSigProfileDescriptionTag, "AdobeRGB 1998 virtual profile");
cmsAddTag(hProfile, icSigDeviceModelDescTag, "AdobeRGB 1998 built-in");
return hProfile;
}
Hope this helps,
Marti Maria
The little cms project
http://www.littlecms.com
[EMAIL PROTECTED]
----- Original Message -----
From: "Stuart Nixon" <[EMAIL PROTECTED]>
To: "Marti Maria" <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>
Sent: Sunday, August 08, 2004 2:35 PM
Subject: Correct "Generic" Monitor profile for Mac/PC?
Marti & others:
I need to create some default "generic" monitor profiles
for an application. These are for CMS display output for
when the user does not have a calibrated profile for their
display.
I'm trying to establish what the generic display profiles
should be.
For PCs, I would think it should be:
Gamma 2.2, D65 WP, sRGB gamut projection
And for Macs:
Gamma 1.8, D65 WP, Apple RGB gamut projection
Questions I'm trying resolve:
1. Can anyone confirm or correct the above?
2. The description for Microsoft's Generic Monitor G2.2 D65
suggests it uses Adobe RGB (1998), yet other generic
display profiles use sRGB, which I would think makes more sense.
3. I'm certain that the Mac uses Gamma 1.8. I'm not sure what
white point should be used. Some documents say that Mac's use
D93 WP, where as generic profiles Mac G1.8 profiles I've seen use D65.
Any input on this would be appreciated. These are to build default
internal profiles for when the user or system has not specified a
profile for the monitor.
Regards
Stuart
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