From: "doodlebun" <gbleser@bellsouth.net>
Date: May 19, 2008 12:25:00 PM MDT
To: Astro_IIDC@yahoogroups.com
Subject: Use of Histogram expand and color balance techniques
My wife and I use Astro IIDC with the DMK21AF04 and Astronomik LRGB
filter wheel for imaging Saturn. My wife feels that she gets the best
results leaving Histogram expand on to achieve proper brightness on
all channels.. I feel that it can give Astro IIDC fits.
My understanding is the proper way to achieve color balance is:
Take a bunch of movie frames of an out of focus G2V star using the
monochrome camera. Start with some red frames through a red filter,
making sure the image is not clipped. Do the same with G and B
filters, taking care to not allow the exposure to change by keeping
all "auto" functions disabled in Astro IIDC.
Use photoshop to determine the intensities of the R,G and B
components in each image. From those intensities one derives
the "boost" value given to the dimmer G and B channels of the tiffs
generated from stacked Saturn channels.
This method means that the RED channel of Saturn is filmed first,
as bright as possible without clipping. Then a green and blue movie
is filmed without altering any gain, or any other setting period. The
blue movie will be quite dim in the series. There is a strong
tendency to boost gain or exposure time, but it seems that would
throw the whole color balance scheme into confusion.
Use photoshop to increase the gain in each channel according to the
test results from the G2V star. If everything is done correctly then
you should get rings of Saturn that are actually "white" like they
are supposed to be. And there will be no reddish bands on the planet
like I have been getting.
Before I proceed with this, I sure would appreciate some comments
for myself and my wife Gail.