[Mp4-tech] question on VUI transfer characteristics

[hudson deng]

Hello,
  I'm studying the VUI part of H.264 and found there are two quite special opto-electronic transfer characteristics, the logarithmic 100:1 and 316:1. I think they are special because they two are logarithmic while others are power functions. And I found that there is no such transfer characteristic defined in ISO 13818-2 (2000 version). 
  here are my questions: 
    what's purpose of these logarithmic transfer functions?
    where can I find their initial definition (just some doc like BT.709/SMPTE 240M)?
    in what situation they will be used?
  Any guideline to find further info is welcome.
  Thank you!
  Hudson Deng
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