"note: gamma here is a different stuff from those used for contrast for those not familiar" - Actually, it's substantially the same thing Ryuji.(posted 8059 days ago)
Since sensitometry curves are all plotted log/log, even the 'straight line' portion of a film curve follows a power law (gamma function). Only when film is developed to a gamma of one is it truly linear.
A gamma of 0.7 on a film sensitometry curve has exactly the same meaning as a gamma of 2.2 applied to a computer monitor. It's just that when converted back to a linear form, a gamma < 1 means that the curve has a positive hump, while a gamma >1 has a negative dip - that's all.As an interesting aside to this: If we developed our negatives to a gamma of 0.45, it would almost exactly cancel the (sRGB) gamma of 2.2 of a computer monitor, and we'd get a linear translation of brightness from subject to output device.
(This is probably why I prefer to have my monitor set at gamma 1.8; the reciprocal power of 0.55 is much closer to a normally developed film gamma.)