Star Mask, Star halos & noise

[mcbbcn]

Hi Ivo,

Thanks a lot for the tips.

I was able to get rid of those red/blue pixels, and for the 3-5 stubborn ones using RGB Blur, and then I used the 'Heal' module at the very end for the few left, as you suggested.

Regarding the star colors, I tried to apply a star mask around the halos since the RGB creation to see if I could protect them through the process (specially during Wipe's), but they did not popped out. So, just for kicks, I did the RGB combine and DBE for gradient removal in PI to check if I had any star colors, and then I could see the star colors, so I'm not sure why I'm not getting them in StarTools for red & yellow stars, but I'll let you play with it, and I look forward to your results.

Yet, I'm extremely happy with my last process. As you can see, I'm getting closer to your processing of this object & I found myself processing very fast & enjoying the processing process unlike the pain that I was feeling with my previous tools.

Here is the outcome....

[mcbbcn]

Hi Ivo,

Just for the sake of experimentation, I created the RGB in PI, which include DBE, Background calibration & color calibration, then I did the rest of the processing in StarTools & I was able to get star colors in the red, blue & yellow ranges. I still like the processing more in StarTools as well as the overall outcome, but I just wanted to run this test to see if I could pull star color. I look forward to hear your results, as I would like to be able to do all the processing end-to-end in StarTools.

See the result....

Thanks for your help,

M.

[admin]

It can be done in ST. It's just that your RGB data is very noisy and has a lot of gradients.
This is what I did;

Create RGB using LRGB, keep default values
Bin to 50%

Wipe, Parameter [Top End Treatment] set to [Wipe 2.0]
Auto Develop, Parameter [Ignore Detail <] set to [1.5 pixels]
--- Color
Parameter [Saturation] set to [580 %]
Parameter [Blue Ratio] set to [1.10]
--- Color
Parameter [Saturation] set to [773 %]
Parameter [Blue Ratio] set to [1.12]
Parameter [Green Ratio] set to [1.40]

Save RGB
Create LRGB composite

Parameter [Cap Green] set to [Yes]
Parameter [RGB Blur] set to [5.0 pixels]
Parameter [Green Ratio] set to [1.35]
--- Wipe
Parameter [Dark Anomaly Filter] set to [2 pixels]
Parameter [Aggressiveness] set to [81 %]
--- Wavelet De-Noise
Parameter [Scale 1] set to [100 %]
Parameter [Scale 2] set to [100 %]
Parameter [Scale 3] set to [100 %]
Parameter [Scale 4] set to [100 %]
Parameter [Scale 5] set to [100 %]
Parameter [Color Detail Loss] set to [50 %]
Parameter [Brightness Detail Loss] set to [17 %]
--- Color
Parameter [Cap Green] set to [To Yellow]
Parameter [Green Ratio] set to [1.20]
--- Wavelet Sharpen
Parameter [Channels] set to [Brightness & Color]
Parameter [Scale 1] set to [100 %]
Parameter [Scale 2] set to [100 %]
Parameter [Scale 3] set to [100 %]
Parameter [Scale 4] set to [100 %]
Parameter [Scale 5] set to [100 %]
Parameter [Amount] set to [90 %]
Parameter [Small Detail Bias] set to [98 %]
--- Life
Isolate preset
Parameter [Strength] set to [50 %]
--- Wipe
Parameter [Cap Green] set to [To Yellow]
Parameter [Dark Anomaly Filter] set to [3 pixels]

The following fades the color in dark parts of the images to greyscale;
--- Layer
Parameter [Layer Mode] set to [Desaturate fg (Luminance)]
Parameter [Brightness Mask Mode] set to [Where fg is light, use bg]
Parameter [Brightness Mask Power] set to [0.20]

--- Color
Parameter [Saturation] set to [133 %]

Miquel_Heart_PreLife_Post2_StarColour.jpg (474.47 KiB) Viewed 12540 times

[mcbbcn]

Got it!

At the beginning I thought you were joking with the 1200% in saturation, but I was surprise when I saw the final image. Yes, the image colors are there, but obviously, it looses some of the refinement because it's a balance on what you've called out with gradients & noise. In the end, it's just 45min. Ha, and 15min. for each color, so the noise was going to be a given...

I went ahead & followed your steps with a couple of tweaks...Thanks for all the lessons. I'm getting very comfortable with the tool very quickly.

By the way, do you have any tips when the star halos loose their roundness and start looking a bit more rough?

Thanks for all your help,

M.

[admin]

Got it!

Nice!

At the beginning I thought you were joking with the 1200% in saturation, but I was surprise when I saw the final image. Yes, the image colors are there, but obviously, it looses some of the refinement because it's a balance on what you've called out with gradients & noise. In the end, it's just 45min. Ha, and 15min. for each color, so the noise was going to be a given...

The insane increase in saturation is only needed because the normally white cores have noew been coloured every so slightly by the Magic module. It requires *a lot* of saturation to turn that very pale off-white into the real star color!
The trouble is that the RGB signal doesn't match our synthetic luminance (which includes a huge chunk Ha), so the luminance is trying to bring out detail where there is not enough (reliable) signal for the color to exhibit the same amount of detail. It's normally not such a big deal, as the human eye is less sensitive to color information, but when scales are very small (e.g. widefields) that unreliable color information starts to lead to stars having no color or incorrect colors.

I went ahead & followed your steps with a couple of tweaks...Thanks for all the lessons. I'm getting very comfortable with the tool very quickly.

It's easy to see your are getting very proficient very quickly Miquel. And if anything is unclear, remember I am here to help!

By the way, do you have any tips when the star halos loose their roundness and start looking a bit more rough?

If that happens, you may want to switch the noise reduction algorithm from Median based to Gaussian/Diffusion. The noise reduction is trying to retain a rough shape for the star halo, but that shape seems to becomes too rough. Diffusion does not attempt to retain a shape at all but diffuses pixel information to neighbouring pixels.
Also be careful with Wavelet Sharpening - create an inverse star mask that has such problematic stars deselected, otherwise the sharpening may accentuate the rough looking halos.

[mcbbcn]

Very cool! Thank you sir! By the way, I just noticed something, you said that the cores were slightly colored by the Magic module, but I did not see the Magic module called out in your steps...Is that something that I was supposed to do? Thank you. M.

[admin]

Very cool! Thank you sir! By the way, I just noticed something, you said that the cores were slightly colored by the Magic module, but I did not see the Magic module called out in your steps...Is that something that I was supposed to do? Thank you. M.

Oops! Yeah.
The reason why this works without the Magic module in this instance, is because we created a synthetic luminance that included Ha - this will make cores not completely white to begin with, combine this with colour blurring and noise reduction and your cores will be slightly colored.

[mcbbcn]

OK, so if I did not have Ha signal, let's say a shot from an exposure made with my OSC camera, please could you share where would you usually introduce the Magic module in the process. I'm going to assume that it's after the image has been stretched (aka non-linear) and after de-noising...and what kind of (most of the time) values will you work to process an image with Magic module. I'm asking because I've never used this module, but I have a few OSC shots, that I could probably reprocess and see how it goes. Thanks for your direction! M.

[admin]

OK, so if I did not have Ha signal, let's say a shot from an exposure made with my OSC camera, please could you share where would you usually introduce the Magic module in the process. I'm going to assume that it's after the image has been stretched (aka non-linear) and after de-noising...and what kind of (most of the time) values will you work to process an image with Magic module. I'm asking because I've never used this module, but I have a few OSC shots, that I could probably reprocess and see how it goes. Thanks for your direction! M.

No reprocessing needed Miquel - the Magic module is definitely a last-step sort of post-processing tool.
The Magic module is meant for manipulation of star appearance and there are a number of algorithms that you can use.
'Shrink' is useful to shrink stars. It is best applied when star fields in wide-field images detract from a DSO. It is also useful to subtly make blown out stars appear less blown out.
'Tighten' is a variaton of Shrink where everything but the star core is being shrunken.
'Shrink Core' draws color into a star's core by progressively adopting surrounding pixels for the overexposed core. This is the setting you'll want to give color to star cores that are completely white.
'Expand Core' makes star bigger. Probably not very useful.

[mcbbcn]

Got it! Thanks a lot Ivo!