Finally, I will not change the gamma and the levels, because I tried something and I understood !
I add scanlines on one of my picture, and when I observe, it was equivalent to the same picture with the gamma to 2.5 instead of 2.2.
So, I conclued that the scanlines from the CRT screen affected the gamma and the general luminosity of the picture. And it's not a question of levels.
A gamma of 2.2 on a CRT looks like a gamma of 2.5 on a modern display, because of the technology that it used.
The other problem is, that I shoud change the gamma for all my videos, and I don't think it's the good thing to do. It's better to calibrate a screen to a certain gamma rather than to change the gamma of videos.
And if Higan propose to have a color filter that we can activate or not, it's just for a certain representation of what the CRT were. It doesn't respond to an objective will.
Voilą ! J'ai tout dit !
(I know it's not exactly representative of the reality, but these pictures are just for the examples)
Mr. Nutz - Scanlines vs. Original
https://media.joomeo.com/original/5af843d4308eb.png
Mr. Nutz - Scanlines vs. Original (gamma changed for 2.5)
https://media.joomeo.com/original/5af844264413d.png
Mr. Nutz - Scanlines vs. Original (gamma changed for 2.5 and luminosity adjusted)
https://media.joomeo.com/original/5af8445997808.png