Xref: utzoo comp.graphics:4153 comp.windows.x:7353
Path: utzoo!attcan!uunet!jvc!jonathan
From: jonathan@jvc.UUCP (Jonathan Hue)
Newsgroups: comp.graphics,comp.windows.x
Subject: Re: Luminance from RGB
Message-ID: <200@jvc.UUCP>
Date: 17 Jan 89 23:05:09 GMT
References: <23105@apple.Apple.COM> <2263@eos.UUCP> <83604@sun.uucp> <85366@sun.uucp>
Organization: JVC Laboratory of America
Lines: 16


I'm slightly puzzled by these calculations of luminance from RGB.  Doesn't
the formula Y = .299R + .587G + .114B only apply when RGB represents
intensity, rather than pixel values?  If your pixel values are completely
gamma-corrected through look-up tables in your frame buffer hardware so
they represent intensities, this would work, but if you use linear look-up
tables (or don't have any), you would need to convert pixel values to
intensity, calculate luminance, then convert them back into pixel values
(voltages).

Also, considering how far the green of the typical color monitor is from
NTSC green, it may be worth deriving new coefficients for the monitor you
are using.


Jonathan Hue		uunet!jvc!jonathan