Thanks for the comments folksI
STEVE333 wrote: ↑Fri Nov 27, 2020 5:34 am
That's a really interesting processing on this target Jim. don't think I've seen all those colors before. Looks like the Seagull ran into a rainbow! Just beautiful. As usual the stars are exquisite.
Steve
carastro wrote: ↑Wed Nov 25, 2020 1:01 pm
Great image, not quite sure how you managed to get 3 colours out of a bicolour image, but great stuff. I like bright colours but even for me I am wondering whether it is a bit too vivid.
Carole
Carole Steve,
Thanks for the comments and I appreciate the feedback. I didn't say anything directly in my responses regarding the vivid color and tonal variation - I wanted to see what people would say. So its good to get some feedback.
The color tone variation is done on the
Ha data. As you know, HOO presentation presents OIII and
Ha as a mixed percentage into the green - traditionally 50-50. So some people have been working on blue enhancement of the OIII data; in this case I have added a tonal variation for
Ha which tends to highlight the higher intensity levels of
Ha toward an orange hue. This is done by setting a threshold and gain on the
Ha channel (mapped into green). In this case I used 0.25 for a threshold and 1.6 for gain. That means that above 0.25 for
Ha,
Ha maps to green at a 60% increase. I do the blue (OIII) enhancement and this
Ha tonal variation in pixel math so my NB mapping is done with one pixel math step after stretching and starless treatment of
Ha an OIII. I can change the factors and thresholds to get a desired mix. My purpose is to avoid the mono-tonal red look that can sometimes occur with heavy
Ha data. So the intent is mainly to highlight higher
Ha levels - much the same that blue enhancement of OIII tends to make the blue "pop".
I appreciate your comments and those of others as well. I will probably tend to lower gain and increase threshold in some of my next Bicolor image processing to avoid startling people with the color. I do think it has some uses though. For example, in the upper left corner (of the "north up") images on the website, there is a bright star with what looks like a comet tail of "red/orange". This star is HD 54359 (which I annotated as TYC5385-1211-1). It is a high proper motion star (kinda like Bernard's star). The tail is opposite (trailing) its proper motion. I am not saying its proper motion creates a higher intensity of
Ha ionization (I am not nearly knowledgeable enough in astrophysics to suggest this and don't really want to spend the time to try to look for scientific papers that do or do not). But the higher intensity
Ha of this "tail" sort of gets lost in a straight
Ha mapping in HOO and in this mapping the intensity comes out.
Jim Thommes
Jim's Astrophotography
David Levy Maksutov Newtonian, Celestron Edge 9.25, FSQ-106N Refractor (on loan), WO ZenithStar 66 APO Refractor, WO Megrez II APO, Sigma 150 mm EOS Lens
Losmandy G11/Gemini, iOptron GEM45, Celestron Advanced VX, iOptron CEM70
ST8300M Camera, Atik 383L, Canon 350D (IR cut modified), ASI1600M, ASI294M, ASI260M
Observatory -
Desert Astronomy Association (Shelter Valley, CA)
