self wrote:
How do I duplicate an underwater photo of a color wheel?


I want to try to correct underwater photos that I took to reflect the
fact that some colors do not show correctly at depth. I took a color
wheel to a depth of 50 feet and photographed it using natural light. [ I
did not use a flash.] I then took the resulting photo of the color wheel
and tried to use Photoshop to alter the color so that it would match the
original.
I can't seem to get the photo of the red sector to look even remotely
like the red original. I do not know much about Photoshop, is my
approach wrong or did I overestimate the ability of Photoshop to restore
the original colors?


The problem is that there is an uneven loss of the colour spectrum with
the red end fading first and so on until everything is in shades of
blue. What you need to do is rebuild the red channel in the photo, this
can be a long and complex process. Here is a link to a tutorial from
the Digital Diver Network (http://www.digitaldiver.net)
http://www.digitaldiver.net/lib_docs/color_cast.pdf

Depending on which camera you are using there may be other ways for you
to improve the colour rendition of your photos. If you can set the
white-balance manually or are able to shoot RAW then you are in luck,
otherwise filters are your best bet with ambient light.

jon