[Tig] fade ins, fade outs.

Richard Kirk richard at filmlight.ltd.uk
Tue May 5 08:56:01 BST 2009


Is rec709 'clipped'?

In digital terms it is not more 'clipped' then conventional log RGBwhich 
go from 0-1023. The difference is in how the colors reach the limit at 
the top end. Film log RGB flattens off gracefully as you get to the 
'toe' of the print stock exposure curve, so you can have highlights that 
clip but still look pleasing. Video, on the other hand, has a luminance 
curve that gets steeper and steeper until it whacks into the limit, 
which can give you rend and yellow bands around your highlights as the 
red, green. and blue channels saturate in turn.

This does not mean there is anything 'wrong' with video as such: it is 
just a standard for processed image data. It was originally designed to 
keep your color telly simple and cheap (simple and cheap when compared 
to a 1950's computer, that is). On the other hand 'log' is a working 
standard with the handy property that you can grade images up and down 
and fetch data from the highlights or the shadows. To some extent you 
can fetch a bit back from the beyond-legal video range when you edit, 
but you still slam visually into the upper limit.

Cheers.
Richard Kirk





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