At 10:46 PM 1/29/2009, C.H.Ling wrote:
>There should be a standard to measure the ISO for digital cameras, I believe
>it check the grey rendering. For example, the grey card should read 128 (?)
>if properly exposed.
IIRC the number for a Kodak gray card is 117, not 128. It has to do
with the gray card having an 18% reflectance and viewing the file in
a 2.2 gamma color space. A Google search would probably turn up the formula.
There's also been talk for years of Canon (and some others) using 12%
gray instead of 18% for meter calibration. Here's a link to an old
article by Tom Hogan on the subject:
<http://www.bythom.com/graycards.htm>
Later,
Johnny
__________________________
Johnny Johnson
Cleveland, GA
mailto:jjohnso4@xxxxxxxxxxxxxx
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