Description:
Although nice bright targets that respond well to fairly short integration times, globular clusters do present some challenges, particularly with sharpness, star shape and natural-looking colours. Using just the basic free processing tools such as GIMP makes achieving consistent results rather difficult.
To counter this, i've tried to develop some pre-processing tools that take out some of the guesswork, based on mathematical descriptions of different approaches I've found on the web.
The basic workflow now consists of:
- Stacking using DSS
- Simple black point adjustment based on identifying the global pedestal levels in R, G and B
- Global white-balance based on average RGB values for stars
- Colour preserving arcsinh stretch
- Non-uniform background correction based on measuring the RGB pedestals on a 20x20 grid covering the image and subtracting a smoothed surface passing through these values
- Final touchup in GIMP (denoising, sharpening, tweaking the stretch)
Overall the approach seems to preserve star colours better and give a more 'natural' look (at least to my eyes). Feedback welcome!
Uploaded: ...
| Caldwell Globular Clusters |
Comments