Stephane,
> How do I figure out the correct RGB weight value in the RGB Worspace interface?
Each image will be different depending on your target. For example, if your target is composed of mostly H-alpha (i.e. red nebulosity), you could go with a R=2, G=1, and B=1. In the end, this will create a ratio of R=0.5, G=0.25, and B=0.25. You're giving red more emphasis in the luminance channel. When there are mixed colors (i.e. reds, greens and blues), I generally go with R=G=B=1. This gives all three channels an equal weight. The RGBWorkingSpace helps you control the dominant color in an image. It will take some experimenting, but you will finally get a feel on what ratios to settle on. I would recommend creating Previews of several of your targets, create several clones of these Previews, experiment with different ratios for each target/clone, and then extract their luminance channel. By going through this sequence, you'll find which ratios give the best result. It's all about compromise. You'll find if you go too far in one channel, other targets will suffer.
I hope this helps,
Wade
