How to Monochrome, Haze video Effect in FFmpeg?
Monochrome

 

One method is to use the hue filter to desaturate.

ffmpeg -i input -vf hue=s=0 -c:a copy output
ffplay -vf hue=s=0 input


De-haze (increase contrast)

 

The curves filter has several presets including a few that increase contrast. You can also make your own curves in Photoshop, export the ACV file and use it via the psfile option in the curves filter.

ffmpeg -i input -vf curves=preset=increase_contrast -c:a copy output
ffplay -vf curves=preset=increase_contrast input