Lightroom: MelissaRGB: Gamma value?

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  • Updated 7 years ago
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As far as I understand, LR uses variants of the ProphotoRGB gamut. Internally for calculations, it uses gamma 1.0, whereas for displaying the histogram and RGB percent values, it uses gamma 2.2 to represent a "natural" distribution of luminance along 0...100%, like AdobeRGB or similar to sRGB.

My question is: Which one of the above is called MelissaRGB? ProphotoRGB with gamma 1.0 or ProphotoRGB with gamma 2.2? Or is it even something completely different?

Note: I posted this question out of pure curiosity... ;-)
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LRuserXY

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Posted 7 years ago

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Lee Jay

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ProPhoto+sRGB tone curve = MelissaRGB
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Lightroom Melissa, Official Rep

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Exactly.
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Chris Cox

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ProPhoto = ROMM = Reference Output Media Metric
ProPhoto + Gamma 1.0 = RIMM = Reference Input Media Metric

(just to complete the list)
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LRuserXY

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Thanks for the replies!

Just to clarify: Based on your answers, I assume that MelissaRGB uses the sRGB tone curve (modified gamma 2.2 with "offset", see http://en.wikipedia.org/wiki/Srgb#The...) and NOT the "pure" gamma 2.2 tone curve of AdobeRGB. Is this correct? sRGB is mentioned in the LR help, too.

I made a quick test using an sRGB image with some defined RGB gray values, and the values match perfectly with the RGB percent display in lightroom, whereas for an AdobeRGB image, there are some differences. So this "experiment" clearly indicates the sRGB tone curve is used for MelissaRGB.

Again, I am just curious about this subject... during normal work in LR, it would not make a big difference ;-)
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Lee Jay

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"I assume that MelissaRGB uses the sRGB tone curve"...Yes.
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Andrew Rodney

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Yes (in that its not using a simple gamma curve of 2.2 but one with that little sRGB curve tweak in the shadows). As such, it ain’t a gamma curve.