At 10:01 AM 4/17/01 +0200, Jez Cunningham wrote:
[snip]
In the book "Photoshop for Photographers" concerning color balance there
is an interesting suggestion that you photograph a grey card (ideally a
Kodak 18 0rey reference) and then use the dropper tool to sample some
pixels on the scanned image. The R, G
and B components should all have the SAME numerical value if there is no
color cast - and presumably should equate to 18%. So by tweaking levels
on the color channels they can be equalized and then by tweaking
brightness and contrast the image can
presumably be 'calibrated' to the gray card.
And then the rest of the photos on the same film should be correct.
I'm not sure this would work. If all of the photos you took on a roll of
film were shot within a short period of time after you photographed the
grey card, and the lighting hadn't changed, then yes, this would be
reasonable. But even over the course of an hour outdoors, lighting levels
and colours can change, making it a necessity to re-shoot the grey card
under the new conditions.
I don't want to take too many pictures of my grey card. ;-)
On the other hand, this suggestion should work quite well under controlled
(e.g., studio) conditions.
Garth
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