Gray cards : the 12% - 18% controversy

Started Apr 13, 2013 | Questions thread
xpatUSA Forum Pro • Posts: 13,152
Re: The grey card is a reference for print making

cquarksnow wrote:

Hi, xpatUSA -

As the gamma for this Melissa RGB (a.k.a. B@stard RGB) is not 2.2 , do you think the MelissaRGBD65.icc profile in Sandy McGuffog's site is nevertheless correct

based on his explanation :

The MelissaRGB profile deserves some explanation. Melissa RGB is not an "official" color space, but is the combination of the ProPhoto color space, with an sRGB gamma curve. It's important because Melissa RGB is what Lightroom uses for its readouts. Specifically, the RGB values you get as Lightroom readouts are in this space. Note that the Melissa RGB profile I'm providing here has the real sRGB gamma curve. The sRGB gamma is close to a 2.2 gamma, but is linear at low values. So, if you take a readout of the darkest patch of the GretagMacBeth chart, there is is about a 1.5% difference between the reading using ProPhoto at a 2.2 gamma and a true Melissa RGB profile.

I looked at MelissaRGBD65.icc with the ICC Inspector utility.

The white point is slightly different than D65 in standard profiles.

The blue thingy is in negative xyY territory! The green thingy is positioned such that it excludes quite a few visible CIE xyY colors.

I don't quite understand what the purpose of the profile is, so I can't say whether it's correct or not. I guess Adobe has its own reasons for b@stardizing Kodaks ROMM and I'm sure those reasons make sense to somebody . . E.C. perhaps.

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