Here is an experiment
about how the amount of color data affects the final LRGB image.
All processing was
done with CCDStack.
The Luminance was acquired at 0.64
arcsec/pixel and the color was binned 2x2. The above LRGB shots
are displayed at 200%, or 0.32 arcsec/pixel.
The sub exposures, all
at 15-minutes, were first normalized and sorted by weight. For
luminance, I used the middle 30 and 15 subs. For color, the
middle 15 and 7 were used.
The final images were
mean combined, all using identical data rejection. For the
luminance, min/max clipping was used and STD sigma reject for the
DDP and color
saturation adjustments were applied using... "apply to all."
In the first two
images, the color data with seven subs, clearly has more noise.
The higher count of hot pixels shows that data rejection works
better with more sub exposures.
Images two and three
show how inadequate color can ruin your smooth luminance background.
The luminance of image three is smoother. However, the noisier color
data has taken over. Image two, with only 15 luminance subs,
actually looks better. This may be improved with selective
smoothing of the color data.
Images three and four
also show how insufficient
color can ruin the your hard work in obtaining many luminance
sub-exposures. Image four is smoother and the color extends
down to fainter stars.
When binning color,
for each two hours of luminance try collecting one hour for each
sub-exposures so that rejection is effective.
asymmetrical Min/Max clipping. It may be better to clip more
on the bottom or top.
If you are not fortunate to have
skies, images two and three may show a good way to go. It can
be useful to cut back on the luminance exposures and concentrate
more on the color.