I took a video with nearly white backgrond.
How can I correct this "nearly white" backgrond to perfect white background.
All the best
Whichever approach you take it'll require some comping.
I'd start by crushing the levels and pulling a luma key his head and hands = matte 1. Then Keylight the shirt = matte 2. Combine matte 1 and matte 2 and you've got a foreground matte. Then place that layer over your original plate, grade the original plate up to a solid white and hope your foreground matte holds!