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.