[DJScotty (Scott)]

Originally Posted by Shiraz

Some methods seem to be significantly more efficient than others (time wise). The attached spreadsheet shows the results of a very simplistic analysis based on scaling to get to the same SNR from the different strategies. Time in hours has been presented for my system for a bright target, but the main point is the relative times of the different approaches, not the absolute time.

The four possibilities summarised in the attached spreadsheet are:
1. Lum + RGB full res where the RGB subs are not long enough to be sky limited – ie they cannot be added to the luminance stack, but may be adjusted for the desired dynamic range.
2. As above but with RGB subs that are also sky limited and that are added to the luminance stack. This approach does not allow the RGB subs to be deliberately shorter to increase the colour dynamic range.
3. Lum + 2x2binned RGB where the RGB data only requires ¼ as long, but has lower resolution, so cannot be added to the luminance – question is, does this lower res introduce any complications?
4. RGB with subs long enough to be sky limited, but with no luminance. This cannot be equivalent to 1. above, so have chosen the time required to get to the same luminance SNR, but with higher quality colour results. It can take a long time to get results, but maybe they are worth the wait?
5. Rick's method - RGB 1x1 subs long enough to add to luminance, then software bin RGB to generate the colour data.

Based on this very simple comparison, there may be significant gains to be made in time required for an image, simply by choosing an appropriate strategy. I have been using strategy 3. above with reasonable results and it is definitely quicker to get to a given result than my previous use of strategy 1. The worst possible efficiency comes with RGB at full res - you never sample more than about 1/3 of the available photons.

Originally Posted by RickS

RGB only imaging can work well, but is best suited to bright targets (or automated scopes with access to frequent clear skies). As Lee noted, LRGB will get you the same SNR in less time.

Cheers,
Rick.

Originally Posted by codemonkey

The difference is that when you're shooting lum, you're getting light from red, green and blue all at the same time, so you're getting better SNR, thus showing up fainter stuff more quickly and cleaning up the noise more quickly.

I combine my RGB with my L, since they're all shot using 1x1 binning; basically throwing away data if you don't.

Originally Posted by Slawomir

Hi Scott,

A good question and the answer is yes, you can and many do it. Easily done in PI with ImageIntegration tool :-)

You can/should also combine narrowband channels to create a synthetic Luminance that will show more info as opposed to using say Ha alone as a Lum.

Here is a link to a bit more detailed discussion: http://pixinsight.com/forum/index.php?topic=6042.15

Rick, Lee, Ray and Suavi,

Thanks for your responses.

So what I am taking away from all of this is:

• Binning 2x2 saves time
• It is possible to do, and is done
• If you decide to actually shoot Lum and then add unbinned RGB data, there is better SNR and thus overall benefit to the image in the end

Definitely something to think about. Thanks gents!