Grading doesn't benefit AT ALL from 4:4:4. It only helps in greenscreening. Oh and theatres are 4:2:2.
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Ummm i have to disagree on both points...
1) DCP spec is 12 bit per pixel, and DCP is what gets screened in theatres, and the standard i work to... hence the Dolby mon, the only screen that shows 12 bit per pixel
2) There is advantages to working with YUV sourced material in RGB, mainly due to creating colors in gradeing that are not discribed by YUV, and monitoring while working in P3 (gammut is far wider than 709) shows colors that just do not exist in YUV.
I do agree that keying / qualifying masks / secondaries is far easier in RGB as well... but the real advantage of working with YUV footage in DCi-P3 is WYSIWYG, something YUV/709 can and will never, ever be
Some light reading;
DCP specs;
http://en.wikipedia.org/wiki/Digital_Cinema_Package
XYZ color space;
http://en.wikipedia.org/wiki/CIE_1931_color_space
