StarMask can be applied to a nonlinear image to create a mask that can be used with linear and nonlinear images. In fact, the StarMask process already includes several parameters to delinearize the image: the shadows, midtones and highlights parameters work just like a histogram transformation applied as an initial step prior to mask generation.
With some practice, StarMask can be used to create a mask including virtually *all* of the stars in an image. In difficult cases you can apply HDRWaveletTransform to a stretched version of the image before StarMask. Rogelio Bernal has recently published a
tutorial where he demonstrates this technique. The HDRWT+StarMask combo is a killer combination. Using it we have been able to create a mask of the M42 region including all the stars within the core of M42 and M43.
Another common source of confusion is deconvolution and its
deringing support image. A deringing support is
not a mask. It works by driving a special routine that limits growth of ringing artifacts at each deconvolution iteration, but it doesn't work as a mask because it does not perform a blend of two images. Fortunately, a deringing support for deconvolution is usually very easy to build: you just need to include relatively bright stars. Jordi Gallego has a nice presentation on his website in PDF format:
http://astrosurf.com/jordigallego/articles/Pixinsight_avanzado_JGallego.pdfThis document is in Spanish but the examples relevant to this discussion are very easy to understand. Jump to slide # 15 and you'll see the typical ringing artifacts that one may expect when applying deconvolution to a linear image. In slide 16 you can see the effect of using our
global deringing algorithm. In slides 18, 19 and 20 Jordi puts a very nice example of global + local deringing using a deringing support image (a star mask including only bright stars). In slides 21, 22 and 23 you can see a comparison of the result before deconvolution, with deconvolution + global deringing, and deconvolution + global + local deringing.
Note that deringing with a deringing support can be used along with a regular mask, which is often necessary for deconvolution to protect low SNR areas. However, a star mask (working as a mask) is almost never necessary for deconvolution.
