I think it's time we revive this question, now that there's support for both LogC and PLogLin (the Josh Pines formula) in Nuke 6.3.
I'm currently doing a film when we want to read plates in Log C using the Pines math. The main reason for doing this in Nuke is that Arri's own Log C LUT (as well as the original Cineon LUT), are really designed for video output. The gamma issue is of course easy to compensate for, but the formula is still designed to set black and white points that give you a contrast suitable for display. The whole concept of a black point is not really suited for converting to a truly linear color space, as it can (and will) give you negative values. What we want is to restore the scene linear lighting information, which is what Pines is trying to do in an intelligent way. The question that remains is what settings are suitable when applying the Pines math to a Log C image. The defaults are designed to work with Cineon images, not Log C. For this reason one should avoid using the PLogLin option on the Read node (as it does not offer any settings to tweak). Instead, read the image data raw and use the PLogLin node for the conversion. As far as I can figure, the log reference value for the 18% gray point is 400, but I'm not entirely sure about the rest. I believe the gamma should be somewhat lower for Log C than Cineon (which defaults to 0.6). Unfortunately my plates aren't all that suitable references for this kind of thing, so if there is anyone out there with awesome math skills, please help us out! /Andreas
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