|  | Re: density change export shake to FCP
by David Coiffier on May 27, 2009 at 3:33:38 pm |
Hey Neil, I could give you some complicated explanations, but you really need is a workaround, isn't it ?
Mine is based on my own video hardware,that is Kona3 HD, but I guess it should equally work for other boards...
The correct video gamma isn't just obtained from RGB values with a single ratio conversion, as claimed by Apple. The wrong way of getting 'right' gamma is to set broadcast monitor gamma to .818, you get when dividing native RGB mac gamma (1.8) by video native gamma (2.2). But as we all noticed, this does not fix density shift. BTW, shift occurs not between Shake and FCP, but rather between YUV output driven by realtime converted RGB values (your Shake broadcast monitor feature) and real YUV coded file, read thru your video board, with no conversion.
My workaround is based on linear HDCAM ramp, captured with FCP. When played back in FCP, profile monitor shows a perfectly linear ramp (flat slope). When seen thru Shake monitor feature, with a monitor gamma set to 0.818, ramp is indeed linear, except in the lowest values where you can clearly see an exponential attack instead of linear attack, causing black too bee too deep, and the linear part to start too late, giving an ovrall too deep gamma as well. So FCP doesn't display too light blacks, but Shake is displaying too deep blacks...
I managed to manually correct the ramp with a colorcorrect node, to get it start at the right place, and with a linear slope all the way.
Now I've done this, I set viewer gamma to .818 and then add my colorcorrect node that gives pretty correct linear gamma. This node is only usefull when working, and you need to remove before rendering, as this correction is only to get correct output on your broadcast monitor. Note that when this node is active, you computer viewer appears way too bright, so you really have to work only with your HD monitor...
My ColorCorrect node is set this way, in TMV values :
master controls : flat
low controls :
Gain V = 2
Gamma V = 1.17
mid controls :
Gamma V = 1.17
Hope I was clear, and this workaround will be useful, cause it's a real issue when color timing with Shake...
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