Hi folks. My first time posting in this forum as I didn't feel ready to share my beginners efforts until now. I am however quite happy with this image of M83.
6.5hrs of OSC data shot over two nights. Integrated and processed in PI with a final tweak in PS. Interestingly, APP got the colour almost perfect (in my view) after an initial trial integration while PI didn't. I found it quite difficult in PI to extract the colour and achieved the final result via countless iterations of tweaking curves, saturation and detail. Ultimately, I liked the detail that could be extracted using PI. I like the yellow central bar and the magenta and blue arms. I don't like the CA from the Celestron SCT reducer and despite numerous efforts recombining various combinations of the RGB channels, I couldn't reduce the CA. Oh well!
Edge HD 8" with 0.7 R, ASI533MC, Antlia RGB Ultra filter
77 x 300s (6.5hrs)
PI, PS
I see what you mean about the chromatic aberration Alex but the overall colour and detail in the galaxy have come out well so definitely worthy of display.
Great stuff Alex- that’s a fantastic shot. Stacks of detail and well controlled. I get some annoying CA imaging with my c14 as well as found it was accentuated through some of my processes in PI (especially GHS). Im sure there’s a solution somewhere tho. But even so, I didn’t find it distracting in your image.
Hi Rodney, Michael and Marcus and thanks for the feedback. Being a comparative newbie to PI, I found it challenging to get decent colour regardless of whether I used normal histogram, generalised hyperbolic or masked stretching. I've tweak my image to reduce the magenta and enhance the blue slightly - it's subtle but does look better. I'll soon have an ASI294MM mono setup running and will re-shoot M83 using LRGB ... it'll be interesting to see what difference it makes to colour and maybe even the CA too. Alex
Hi Dave and thanks for the feedback. Celestron's EdgeHD reducer does introduce CA but I too am ok with that - everything is a tradeoff. And your experience with PI's GHS reflects mine; it seems to accentuate CA. In comparison, integrating/stretching in APP seems to produce 'cleaner' looking stars without accentuated CA. That said, I prefer using PI despite the huuuuge learning curve (which you're now on too ... tis fun, eh!). Alex
Hi folks. Thanks for your feedback. I reprocessed the data (in PI) but this time separately processed the galaxy and stars. End result: bluer galaxy, ie. less magenta, and less CA in the stars (which are tighter too). It's hard to know when to stop fiddling but that'll do ... for now
Hi folks. Thanks for your feedback. I reprocessed the data (in PI) but this time separately processed the galaxy and stars. End result: bluer galaxy, ie. less magenta, and less CA in the stars (which are tighter too). It's hard to know when to stop fiddling but that'll do ... for now
Hmmm, compared to your original, I think you've diluted your colour depth Alex, especially with the subtle reds and Ha structures. Also, your stars and faint fuzzies are less colourful.
At the risk of being controversial - your original was not overly magenta. It was a fine image with a good balance of colour. By all means, selectively chase down and lessen the CA visible in your stars.
Hi Marc. Thanks for your feedback, it’s very helpful. This is the 4th galaxy I’ve imaged and for each them, I struggled in PI to get colours that seemed ‘about right’ based on my own sense of things and exemplars. APP however produced colour depth for the galaxies that was ‘about right’ with minimal editing and that’s what my initial M83 image was based on. I have much to learn about PI (… it does my head in lol) to achieve the same result as AAP, and all feedback and advice is most welcomed. Alex
You may have already tried this in PI, but a trick I use to remove/reduce CA is to take the freshly stacked image, use Channel Extraction to get the red, green and blue images. Then use Star Alignment to align both the red and blue images using the green image as a reference, now use Channel Combination to put them back together again. Star Align will "distort" the red and blue star images and overlay the colours better.
Thank you, Matthew. A lot of it is due to the power of PI magic. PI does my head in but it can produce great results, even for relative newcomers like me when used with other tools like APP and PS.
Chris, thanks for the hot tip. I literally stumbled upon this tip the other night (YouTube) but have yet to attempt it. I’ll def be giving this a go and this image/data when I get a spare moment, and on the Fighting Dragons (NGC6188) that I’m currently processing. Alex
