Difference between gamma range in different softwares

Hello,

the first step of my retouching process is to set a gamma value between 2.2 and 2.7 in Photoshop (or Elements)

In Photoshop, Capture One, PhotoLine, Capture NX, the range goes from B=0 to W=255, middle being 1 (i.e. non linear scale)

In GraphicConverter, Pixelmator, Aperture and anything with a Quartz engine, the range goes from B=-1 (or -1.5) to W=+1 (or +1.5), middle being 0 (i.e. linear scale)

Have you any explanation for the different approaches ?

If I want to use Aperture, what gamma range should I use ?

Thanks a lot for your help.

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Christophe Boudier