[Tig] Apple Color strange behavior

Rob Lingelbach rob at colorist.org
Thu Aug 12 17:51:10 BST 2010


[ admin note: the images Anne refers to below as attachments are on the TIG wiki at
http://tig.colorist.org/wiki/Apple_color_anomaly1 ]


I am not familiar with Apple Color behavior and am looking for an explanation/work around for an odd behavior.

I created a 16 bit tiff file (using Matlab) containing a gray ramp, i.e. code values from 0 to 65535 in each RGB channel in a linear horizontal ramp (so no gamma encoding).  When I input this into Apple Color, I therefore expect it to show me linear relationship in the RGB scopes. 

Instead, I see a curve that appears to have a gamma of 1.22.  I have attached a figure of the RGB scopes below.  If I intercept the signal Apple is outputting to the grading monitor, it confirms this gamma 1.22 curve is indeed being transmitted to my grading monitor. 

However, when I render it out of Apple Color without any grading, the line is linear again (see figure below)!   As far as I can tell, this is therefore independent of the display LUT used within Color.  What concerns me then is that what I render is not what I saw on my monitor.  The Apple Color output being sent to the display does not correspond to what’s rendered out for that display. 


Can anyone explain why Apple Color is adjusting the gamma on input?


Linear 16-bit tiff ramp as input by Apple Color (gamma of about 1.22 for some unknown reason):

Ramp values once rendered as DPX and saved as 16 bit tiff via Photoshop (it’s linear again):

[ see http://tig.colorist.org/wiki/Apple_color_anomaly1 for these 2 images --admin ]

----------------------------------

Anne Webster

Staff Engineer, Image Technology Research

Dolby Canada

2985 Virtual Way, Suite 150

Vancouver, B.C. V5M 4X7, Canada

T  604-215-6845

F  604-215-6900

www.dolby.com | anne.webster at dolby.com


--
Rob Lingelbach
rob at colorist.org




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