Showing gamma correction value in usual form

[konstantin_hu]

I would like to know/ask for, how can I determine the accurate value of applied gamma correction (when it is set on Tools/Effect and Filters/Video Effects/Image Adjusts/Gamma). The usual value in video processing applications is in range 0.0-1.0-2.0, for example 1.2

I would like to preview videos with gamma correction applied, and then encode them with ffmpeg CLI application, setting the determined value.