Hi Dave,
Sorry for being unresponsive. These days I'm working like crazy trying to get PI 1.5.5 ready for release. With some difficult bugs and all the new features, I'm having a hard time trying to keep myself synchronized with the forum.
As you already have discovered, a mask protects where it is black, so you indeed need an inverted mask (black stars, light background) to protect your stars.
Building a good star mask is in general a difficult task that requires a lot of practice. This is probably one of the most complex topics of image processing in astrophotography. We have a number of tutorials that can help you. First an entry-level example:
http://pixinsight.com/examples/intro/dbosch-ha/en.htmlIn the above tutorial, skip to section "5.1 Star Mask", where the author describes a simple but effective method for star mask generation based on wavelets.
Here's a similar but more sophisticated technique (skip to "Controlling Star Sizes: Morphological Transformations"):
http://pixinsight.com/examples/M45-sonnenstein/en.htmlTo the purpose of controlling stars during HDRWT, I think you have enough power with these wavelet-based star mask generation techniques. Along with these, we have the StarMask tool. StarMask allows you to select virtually
every star in your image, but it is a complex tool. I describe it in this tutorial:
http://pixinsight.com/examples/deconvolution/Gemini-NGC5189/en.htmlSkip to "Section 7, The StarMask Process", where you'll find a thorough description of this tool with examples. As I've said this is a complex tool, but it is much more accurate and flexible than wavelet-based techniques.
If you want, you can upload your image and I'll be happy to try my hand at building a star mask for you. This can be a helpful example for all forum members.
