Re: Curves and Bit Depth - was Sigma fp
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Ben Allan ACS
Of course, Linear is different to Rec.709. Current display technology can’t reproduce a true linear image - ACES is an example of true linear encoding and how it looks. I think the confusion about this was born with Kodak calling their original LUTs a LOG to LIN conversion meaning that it was - “more linear than LOG” ;-) Kodak though, also accurately described Cineon LOG as a "log-like” exposure response - ie. not strictly logarithmic.
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The other thing is that there is also a difference between mathematical log for storing data and visual LOG for creating a more grade-able image. Most RAW formats use mathematical log to store the data but this needs to be converted into either a visual LOG format or something else like Rec.709 for playback. These visual LOG curves are much more subjective and often go wrong when the designer tries to makes them too mathematically correct. This subjective element is also why each manufacturer has their own LOG curve with it’s own LUT’s. If they were all mathematically logarithmic then you could use the different manufacturers LUT’s interchangeably. Because non-RAW recordings require in-camera image processing, many cameras do this at least at 14-bits because processing at higher bit depth than the input or output will produce more accurate results if any conversion is taking place. Another thing worth remembering is that LOG recordings are called “compressed” in the sense that the compress a wider dynamic range into the same recording dynamics than a more linear format would. This is a completely separate issue to data compression. _______________________________ Ben Allan ACS CSI Producer | Cinematographer | Colorist ACS National Secretary Host of "The T-Stop Inn” Podcast
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