Lightroom colour space(s)

[tenmangu81]

Hi,

I was told some years ago that the colour space of the development module of Lightroom was "Melissa RGB" (Prophoto with an sRGB "gamma"). According to the Lightroom user manual, it is merely Prophoto (i.e. with a gamma of 1.8). For the Library module it is mentioned as Adobe RGB. I guess the calculations are all made with a linear gamma (= 1).

Am I right ? Is Melissa RGB still valid or not ? What are the gamma values of each of those ?

Thanks !!

[TheDigitalDog · Accepted solution]

http://digitaldog.net/files/18Color%20Management%20in%20Lightroom.pdf

Previews in Develop are working in its internal color space, which is Linear encoded "ProPhoto" (RGB primaries). In terms of color gamut, Linear ProPhoto, ProPhoto RGB, and Melissa RGB all have the same color gamut because they use the same set of RGB primaries from ProPhoto RGB. The difference between them is the encoding of the image values (e.g., linear encoding, 1.8 encoding, and 2.2 encoding, respectively). The differences in this encoding does not affect image appearance in previews. So, within the Develop module, how our images appear in Linear ProPhoto, regular ProPhoto, and Melissa RGB are all correct and all the same and for all files: raw, jpeg, tiff, dng, etc. The facts are however, in Develop, the previews are the unnamed internal color space. 

The Library previews are Adobe RGB (1998), because the previews are stored as JPEGs. JPEGs are 8-bit, inappropriate for a wide gamut color space like Linear ProPhoto, ProPhoto RGB, and Melissa RGB. Using an intermediate-sized color gamut as found in Adobe RGB (1998), avoids artifacts, while providing a larger gamut than sRGB. Another reason why the LR user might consider a wide gamut display that closely approaches or exceeds Adobe RGB (1998). 

The Develop module doesn't have quantization problems because the image rendering isn't using JPEGs. It is instead performed on the fly using the original image data (e.g., a raw file), using higher internal precision (at least 16 bits). 

Within the Develop module, if a user has turns on soft proofing, the gamut is limited to whatever ICC profile the user has chosen for soft proofing. 

[tenmangu81]

Thanks a lot you for your answer. I see that not much has changed since the beginning of Lightroom, then (I started with Lightroom 2). The pdf you gave us the link is very informative, even if a little bit old, but still valid.