From: akelly5190
Sent: Thursday, June 20, 2002 3:22 PM
To: SBIG@yahoogroups.com
Subject: [SBIG] AIP4WIN L/RGB Processing

Hi Folks,

Bert's comments the other day and several private questions I have 
received from people on this and other lists cause me to think that a 
short public tutorial on how to really use the AIP4WIN color modules 
might be useful.  Here's the basic procedure:

1.  Process the luminance first to the desired stretch, sharpening, 
etc. (save it), then load the processed and saved luminance image and 
the calibrated (but otherwise unprocessed) RGB stacks (they must all 
have the exact same array dimensions).

2.  Activate the COLOR/PROCESS RGB drop-down. Select the LRGB images 
into the correct fields and the activate the REGISTER RGB IMAGES 
bar.  Use 2-star registration to register the RGBs to the L.  Once 
they are registered, enter the desired RGB weights (preferably 
derived from a Solar-analog calibration exercise <g>) and the average 
altitude above the horizon that the images were made and activate the 
CORRECT BALANCE bar.  (One note here: the RGB weights are the inverse 
of the multiplier weights that folks usually discuss...i.e., if 
your preferred R:G:B multipliers are 1:1:1.5, then the AIP weights 
would be 1:1:0.667).  Images named "red", "green", and "blue" will be 
produced.

3.  Activate the COLOR/JOIN COLORS drop-down. Select the red, green, 
blue, and L images into the proper channels. Hit the RESET TO 
DEFAULTS bar to ensure that *no* stretching is done to any of the 
channels!  Bring up the L/RGB color composite by activating the 
CREATE NEW COLOR IMAGE bar, then activate the BLACK SKY bar to 
neutralize foreground sky color (note: the BLACK SKY bar sets the 
low value of linear stretches on the RGB images to values just below 
the mean background sky ADU in each image.  Activate the SHOW MANUAL 
SETTINGS bar to see the new low values for the RGBs.  The high values 
for the RGBS and the L should still be at 65535).  If the S/N of all 
images is good and the color balance weights are accurate, you should 
be about done..:).

4.  If color is blotchy (low S/N in the chrominance images), activate 
the CUSTOM SETTINGS bar and increase the COLOR NOISE REDUCTION 
function.  If the background is still a bit blotchy, manually reduce 
the low values in the COLOR CHANNEL ENDPOINTS.  If chrominance is 
still noisy, then you should go back to your red, green, and blue 
images and Gaussian blur them before compositing. 

5.  As a rule, if you were happy with your original luminance 
processing, the LUMINANCE FRACTION should stay at 1.00.  COLOR 
SATURATION can be increased to taste, but 1.00 should be good.

6.  As a rule, the high values of the COLOR CHANNEL ENDPOINTS should 
be kept equal.  All at 65535 should be fine, but you should 
experiment with lowering them all equally (if you are happy with the 
color balance) to see what happens with the star colors.  Some people 
prefer brighter stars to have less hue and as the high values 
approach the ADUs of the brighter stars in all three colors, 
they will approach white.  Making the high values unequal changes the 
color balance....experiment with the colorful ADJUST COLOR buttons 
and watch the high values change.

7.  Save the completed composite by exporting it as a TIFF.

Hope this helps a bit.

Kind Regards to All,

Al K.