[Tig] P3-DCI to rec709

Patrick Inhofer elists at fini.tv
Thu Jun 16 16:42:29 BST 2016

> So, by using a LUT that takes you most of the way... Would that LUT also
> 'convert' the white point? Resulting in that the TV will look closer to the
> DCI-whitepoint. Or should one not make the TV-white look like
> projector-white?

One of the things that define a Color Space is white point (or more
accurately, the R G B primary points). When moving between color spaces,
you're also resetting to the RGB primaries defined in that color space...
which have the net effect of remapping your White Points. So yes, a
suitable LUT will make sure white looks like white in the color space it's
remapping into.

​To expand on Marc's comment: In my limited experience grading on
projectors - I absolutely make different decisions than with the same
material on a direct view display... and it ain't just the gamma difference.

With pupils wide open on a relatively dim screen, I'm working in those
middle shadows with much greater effect. On direct view, with pupils closed
down, those details get murky and I'm working the middle to brighter values.

At the SMPTE HDR demo on the Friday before NAB this year it was interesting
to hear the film colorists talk about how HDR opens up the shadows for them
much more than SDR. But when you talk to colorists grading on the Sony or
Dolby direct views, it's all about the pop in the highlights and enhanced
contrast / enhanced perceived detail... the more things change the more
they stay the same - different display technology has us focusing on
different areas of the image.

So P3 vs Rec709 is much more than just white point and gamma differences.
It's a human perception difference - which is why Marc recommends doing a
detailed trim pass after doing the conversion. A LUT can't predict how
human physiology effects our net perception of the image when migrating to
different display technology; that's our job. That said - budgets are what
they are and sometimes all you can do is the conversion and quick trim
tweak and call it a day.

- patrick

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