An introduction to astro image processing

1. An Introduction To Astro Image
Processing
February 1, 2019
Mark Casazza

2. Astro Imaging has 3 Distinct Processes
Acquisition
Pre-processing
Processing
Science - Comes down to Time and Money
Art - More influenced by Skill and Taste
Science
Science
Art and Science
Mount, Camera, Telescope, Guiding, Polar Alignment
Software, Dark Library
Practice, Understanding, Software, Practice

3. Why Start with the Last Process?
● When I revisit old data and reprocess it I always end up with a better image
● I spent much time stressing over what ended up being a gap in processing skills
● Turn what little (data) you have into the best (image) it can be
● How can I practice before I even capture any data?
○ http://www.mistisoftware.com/astronomy/index_fits.htm Link to Mitsi (about 50 images)
○ Link to Yahoo groups (60 images)
■ Search for the group dslr_astro_image_processing
■ Then look for Challenge posted
○ http://www.astropix.com/html/i_astrop/practice_files.html (5 images)
○ https://www.astrobin.com/forum/c/astrophotography/other/all-my-raw-files-are-or-will-be-public-online
/
■ https://drive.google.com/drive/folders/0B9-mgz7OQ4fnYzJHLTdwZzRldEU (too many to count)
○ http://www.rawastrodata.com/ (22 images)

4. High Level View of the Process of Processing
● Global non-Linear Stretching
○ Digital Development
● Gradient, Amp glow, Vignetting removal
● Local non-Linear Stretching
○ Use of masks to focus effects
● Correcting Color and Increasing Contrast and Saturation
● Noise Reduction
Art: What to do in what order and to what extent?
What works for one image will not work for the next
You need to develop an understanding of how things build on each other
Goal: Reality, Scientific, Art, Pretty picture, etc.

5. Global Non-Linear Stretch (aka Digital Development)
● Major impact to darker shades to brighten them up
○ 5 to 20
● Minor impact to brighter shades
○ 30 to 31
● Possibly even dim down the brightest objects
○ 255 to 250
● Never curve back on yourself!

6. Gradient Removal
● Vignetting - Flats only do so much
● Sky brightness
● Amp glow - internal camera effects

7. Pulling out details - Localized changes
● Masks are tricky to get right
● Automation tools help with star masks
● Astronomy focused tools have unique algorithms for this challenge

8. Color Correction and Increased Saturation
● Camera sensors do not see like our eyes
○ Cameras are much more sensitive to red and infrared
● Light pollution filters can mess up color balance
● Colors are subtle in reality, cranking up saturation is visually pleasing

9. Noise - We have been fighting noise at every step
● Pure software feature; your product will do the work
● Star Tools - unique approach
● Photoshop - minimal stock capabilities
● Plugins - I love Colormancer’s Boundary Noise Reduction

10. Before the demo
● Want to learn more?
○ Watch this video: http://www.astronomersdoitinthedark.com/dslr_llrgb_tutorial.php
○ Read this site: http://www.astropix.com/html/j_digit/toc_dig.htm
○ Ask me about further exploring this topic outside of our regular meetings