I think I understand what you're saying, and I understand why you make a difference between the non-linear "RGB" space and the linear sensor space.
But I was simply nitpicking on the usage of the term "RGB space" in this sense.
RGB space simply mean a color space made up of three values, one for red, one for green and one for blue. That's all it means. It says nothing about linearity, so you could have a linear "RGB space" or a non-linear "RGB space".
For that matter, it doesn't even say what "red", "green" and "blue"
are. It's a pretty generic term.
See how Wikipedia defines
RGB space: "
An RGB color space is any additive color space based on the RGB color model. [...] The complete specification of an RGB color space also requires a white point chromaticity and a gamma correction curve." (emphasis mine).
So, "an" RGB space can very well have gamma=1.0, and be linear with the input data - if the input data were produced using a sensor that, in turn, has a linear output, of course.
It says then: "
As of 2007, sRGB is by far the most commonly used RGB color space". Now this is "an" RGB space, and one where the non-linearity is present very well defined: "
The overall gamma is approximately 2.2, consisting of a linear (gamma 1.0) section near black, and a non-linear section elsewhere involving a 2.4 exponent and a gamma (slope of log output versus log input) changing from 1.0 through about 2.3".
Can you have linear RGB? Of course you can, just use a linear sensor and then apply no gamma. Or use a non-linear sensor and then appy gamma to compensate the non-linearity. My scanner natively outputs something that very closely approximates linear RGB, although the driver software then converts it to something closer to sRGB.
