Levels corrections like in Photoshop

[jeeg]

Hi!
Something I use a lot are the levels adjustment in photoshop (CTRL+L).
Xnview has levels corrections but are differente and less useful.

In Photoshop I have three arrows to change the levels, the white arrow, the black arrow and the gray arrow.
In Xnview I have only the white and black arrows.

What happens? It happens that without the grey arrows I can't adjust the midtones...and so I can't adjust the lightness of the image without changing the black and white point.

Is it possible to improve the levels panel in Xnview? So I don't need to open photoshop every time and use Xnview directly?

Please!!