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Hello all, I’ve been doing AP for about a year now and like to think I’m starting to get the hang of acquiring and processing my data. I am very critical of my photos and spend a lot of time and effort behind the computer screen for this hobby. I eventually want to make prints of my work, but before I do that I want to make sure that my processing skills are as good as they can be. I am starting to become very proud of my work. But everyone sees things differently, and I want to make sure that I’m creating work that not only I am happy with, but that is fundamentally well processed - not blowing out stars, not too much deconvolution, overstretching, etc. So I am asking for constructive criticism, and to please be as nit picky as possible. No hurt feelings here  M31 - https://www.astrobin.com/i1g1f5/B/ thank you! |
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| Much too colorful and contrasty. Check your stars' colours don't show LCA. The shadows are a tad noisy (for the stretch applied). |
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I'm in the same boat as you (early into AP) therefore I'm not super advanced enough to comment on your images but I think that you've progressed very well in a year's time! I always scutinize other examples of the target in hand to get an idea of the range of processing potential. It's a blast learning all that's needed in this pursuit! Keep it up! |
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| Nice work! Only a bit of fine-scale color noise is present, which should be easy to fix. Other than that, I wonder if there is more color to to ask for from nearly 28h of data from a very bright galaxy! |
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andrea tasselli: Thanks for your input. By too colorful, are you saying it is over saturated? I do typically prefer more saturated photos but after comparing some of the top M31 pics I felt that I had left some room. Maybe I will bring it down just a bit. Also, can you explain what you mean by LCA? Die Launische Diva: Thank you! I do notice the color noise as well, NoiseX did a good job for the image but I wonder if I could have pushed it a bit harder, or if there is a better tool for color noise specifically. Maybe applying some noise redux with color masks. As far as the color goes, are you suggesting it should be more saturated? I definitely had room to push more but I tried not to overdo it. Of course this is personal preference, especially considering the other commenter mention it was over saturated to them! |
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Thanks for your input. By too colorful, are you saying it is over saturated? I do typically prefer more saturated photos but after comparing some of the top M31 pics I felt that I had left some room. Maybe I will bring it down just a bit. Also, can you explain what you mean by LCA? LCA stands for Lateral Chromatic Aberration which means that the effective focal length at different wavelengths are different (something that happens with optics containing refractive components). In practice this shows in stars' colors slightly mismatched (i.e., between red and blue) and, as the effect is linearly dependent with the field angle, this gets worse the wider the field is (and the image scale). As for colorfulness: your yellows (which is the base color of most galaxies and M31 in particular) are just a bit too saturated. I'd tone them done and improve the red (if you have Ha data this is easier) and the outer blue galaxy's arms. Also, you should try and retain some color in stars, most notably in the bright ones (if they are not saturated to begin with). |
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andrea tasselli:Thanks for your input. By too colorful, are you saying it is over saturated? I do typically prefer more saturated photos but after comparing some of the top M31 pics I felt that I had left some room. Maybe I will bring it down just a bit. Also, can you explain what you mean by LCA? Ahh, I am familiar with chromatic aberration but I've never heard it abbreviated as LCA. What's strange is that this was taken with a very high quality telescope, a brand new Stellarvue SVX080. Aside from my refractor's optics, what else can I do to reduce CA? |
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Ahh, I am familiar with chromatic aberration but I've never heard it abbreviated as LCA. What's strange is that this was taken with a very high quality telescope, a brand new Stellarvue SVX080. Aside from my refractor's optics, what else can I do to reduce CA? You are thinking about CA but this isn't the same and affects most deeply fast optics (either directly or reduced). Chromatic aberration is difference in focus position as a function of wavelength and isn't a field aberration (it is measured at the field center). LCA., on the other hand, changes the focal length itself so the image scale is affected by both wavelength and field angle (albeit for typical field sizes isn't that great) and results in a slight mismatch between position of the red PSF and blue PSF. Nothing too terrible since it can be fixed, by and large, in post-processing. Other than get a very expensive AP or Taka or similar just fix in during image calibration in PI. |
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Lovely image Jay! Now that I see it in higher quality, on my screen, many smaller stars seem to have a green tinge to them. I notice this mostly in the dark regions outside the galaxy. To be clear the image itself does not seem to have any hint of green, just the stars. Not sure why. For Galaxies I typically use SPCC to color calibrate my image and a linked stretch to maintain the original colors. |
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Ashraf AbuSara: Hmm, I hadn't noticed this before but I do see it. When looking at my data, it seems that after I run BlurX on the stars image, they then get that green tinge. It fixes the CA, but adds that green hue. What the heck is that all about! |
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Ashraf AbuSara: Very strange. Is that after application in the linear state? Never seen that behavior before to be honest. |
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Die Launische Diva: You can reduce color noise with PI by using any of the built-in noise reduction tools which allows for targeting the chrominance component. Also, many photo processing software have a chrominance noise reduction tool. Regarding color saturation, this is a personal preference. One good argument for saturated images is when the data supports color saturation, someone should go for it since it will bring up the physical processes behind those colors. For M31 specifically, if you take a look at other respected astrophotographers' images, there are blue regions (star-forming areas). This is because, M31 is somewhere in between regarding galaxy evolution. For your image, some more work on HDR, parallel with color saturation should do. And finally, I believe the tiny green stars is a consequence of the color noise and I suspect that if you reduce color noise, they will be less prominent. |
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Die Launische Diva:Die Launische Diva: Thank you very much for the tips and explanations. I will give this another go sometime this week. I appreciate the comments from everybody! |
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I took advice from this thread and started Adam Block's "Stretch Academy" course, and made another attempt at processing this. I think it turned out much much better and I'd like to hear other people's feedback to see if I've moved in the right direction. I was able to pull out a lot more color and have a slightly more balanced image in terms of stretching. I also removed the green hue from the stars. The stars do still have some issues but you have to look closely to see. Let me know what y'all think - the feedback is very much appreciated and obviously very helpful! Thanks to everyone that has provided constructive criticism thus far! |
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| Hi, it's a great photo. I don't see too many flaws, except that you should pay a little attention to the overall color correction. |
