StarTools

Hi!

I have a question: there is a tool for Photoshop called Hasta La Vista Green! that removes the green noise and green cast from the final images. The green noise and green cast issue as I understand is mainly a DSLR stack/processed image problem, the description of the plugin says:

HLVG is a chromatic noise reduction tool that attempts to remove green noise and the green casts such noise may cause in some images. It is based on PixInsight's SCNR Average Neutral algorithm.

The idea is not new. We all know that with a very few exceptions (some planetary nebulae, comets, etc), there are no green objects in the sky. Therefore, if we've already correctly calibrated and color-balanced an image and it's free of gradients (to the best of our ability at least), we have to assume that if something else looks green in our images it's got to be noise...Don't mistake gradients with noise. Removing gradients are best dealt by subtracting a good background model. Chromatic noise on the other hand is tricky, since it "overwrites" the real data we want.

There are several techniques widely used to deal with this problem, however most of them rely on selections and adjustments that sometimes are not easy to execute. SCNR (the base algorithm used by this plug-in) is in my opinion one of the most reliable methods to deal with "green noise" and it works the same every time, without having to worry about anything, just click OK and you're done.

I use a modified Canon DSLR and I too have the green noise/cast issue, and I don't have Photoshop but I had a license in the past and I can tell you that the plugin made wonders to my images. So is it possible to implement this on StarTools?

Here is the plugin page:
http://www.deepskycolors.com/archivo/20 ... Green.html

Also here is a link to the Pisinsight page about there method with the description of how it works:
http://www.pixinsight.com/doc/legacy/LE ... /scnr.html

So my question is would this be useful to StarTools users (I really think it would) and can we expect this to be implemented? Or maybe I had an oversight and this is already implemented?

Hi,

A very similar tool is already implemented in StarTools; the 'Cap Green' function in Color Module (see here).

"The 'Cap Green' parameter, finally, removes spurious green pixels if needed, reasoning that green dominant colours in outer space are rare and must therefore be caused by noise. Use of this feature should be considered a last resort if colour balancing does not yield adequate results and the green noise is severe. The final denoising stage should, thanks to Tracking data mining, pin pointed the green channel noise already and should be able to adequately mitigate it."


Hope this helps!

I know the Cap Green function but it ain't always doing enough job. With my modified dslr images, the result is still greenish if I cap green to yellow, and the colors go nuts if I use cap green to brown. I will upload some images sometime next week to show you what I'm saying.

MrMxyzptlk wrote:I know the Cap Green function but it ain't always doing enough job. With my modified dslr images, the result is still greenish if I cap green to yellow, and the colors go nuts if I use cap green to brown. I will upload some images sometime next week to show you what I'm saying.

Cap Green (as is HLVG and SCNR) is a last resort tool to remove spurious green color information that can be reasonably assumed to not exist (e.g. an artifact). In general, when following a correct workflow, such artifacts should be very, very rare. If you have large swaths of green in your image at the stage of using the Color module (as one of the last steps), it's typically due to not having correctly color balanced the image, or Wipe somehow failing to correctly remove a green bias.
Cap Green is not a color balancing or correction tool!

Would definitely love to see some images to get a better understanding of what your use case is!

Well. I had finally time to show you this the right way. Here is a link to my Google drive with a ZIP archive and 4 files:
https://drive.google.com/open?id=0B-tkU ... GlNa3lmNVE

The files are:
HorseHead 48x300+10x600.fit -> the original stack without any modification
HorseHead 48x300+10x600_FullRes_AstroToolsProcess.tif -> My full process with StarTools (steps below)
HorseHead 48x300+10x600_FullRes_AstroToolsProcess_PSHLVG.tif -> The above file with Hasta La Vista Green applied on medium settings in Photoshop

My process in StarTools was (from the LOG file):
-----------------------------------------------------------
StarTools 1.4.316
Wed Jun 08 15:35:12 2016
-----------------------------------------------------------
File loaded [F:\Astronomy\HorseHead 48x300+10x600.fit].
---
--- Auto Develop
Parameter [Ignore Fine Detail <] set to [Off]
Parameter [Outside ROI Influence] set to [15 %]
--- Rotate
Parameter [Angle] set to [180.00]
--- Crop
Parameter [X1] set to [4224 pixels]
Parameter [Y1] set to [2796 pixels]
Parameter [X2] set to [1 pixels (-4289)]
Parameter [Y2] set to [35 pixels (-2821)]
--- Wipe
Parameter [Mode] set to [Correct Color & Brightness]
Parameter [UNKNOWN] set to [Yes]
Parameter [Precision] set to [256 x 256 pixels]
Parameter [Dark Anomaly Filter] set to [3 pixels]
Parameter [Drop Off Point] set to [100 %]
Parameter [Corner Aggressiveness] set to [100 %]
Parameter [Aggressiveness] set to [75 %]
--- Develop
Parameter [White Calibration] set to [Use Stars]
Parameter [Gamma] set to [1.00]
Parameter [Skyglow] set to [0 %]
Parameter [Digital Development] set to [90.00 %]
Parameter [Blue Luminance Contrib.] set to [100 %]
Parameter [Green Luminance Contrib.] set to [100 %]
Parameter [Red Luminance Contrib.] set to [100 %]
Parameter [Dark Anomaly Headroom] set to [5 %]
Parameter [Dark Anomaly Filter] set to [3.0 pixels]
--- Deconvolution
Parameter [Image Type] set to [Deep Space]
Parameter [Mask Behavior] set to [De-ring Mask Gaps, Hide Result]
Parameter [Radius] set to [2.5 pixels]
Parameter [Iterations] set to [6]
Parameter [Regularization] set to [1.00 (optimal noise and detail)]
Parameter [Mask Fuzz] set to [8.0 pixels]
--- Wavelet Sharpen
Parameter [Intelligent Enhance] set to [Yes]
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 [Mask Fuzz] set to [8.0 pixels]
Parameter [Amount] set to [250 %]
Parameter [Small Detail Bias] set to [75 %]
--- Color
Parameter [Cap Green] set to [To Yellow]
Parameter [Bias Slider Mode] set to [Sliders Reduce Color Bias]
Parameter [Style] set to [Scientific (Color Constancy)]
Parameter [LRGB Method Emulation] set to [Straight CIELab Luminance Retention]
Parameter [Dark Saturation] set to [9.80]
Parameter [Bright Saturation] set to [Full]
Parameter [Saturation Amount] set to [100 %]
Parameter [Blue Bias Reduce] set to [1.18]
Parameter [Green Bias Reduce] set to [1.16]
Parameter [Red Bias Reduce] set to [1.00]
Parameter [Mask Fuzz] set to [1.0 pixels]
--- Wavelet De-Noise
Parameter [Scale 1] set to [90 %]
Parameter [Scale 2] set to [90 %]
Parameter [Scale 3] set to [90 %]
Parameter [Scale 4] set to [90 %]
Parameter [Scale 5] set to [65 %]
Parameter [Mask Fuzz] set to [1.0 pixels]
Parameter [Scale Correlation] set to [6]
Parameter [Color Detail Loss] set to [12 %]
Parameter [Brightness Detail Loss] set to [12 %]
Parameter [Grain Size] set to [4.5 pixels]
Parameter [Read Noise Compensation] set to [Off]
Parameter [Smoothness] set to [80 %]
File saved [F:\Astronomy\HorseHead 48x300+10x600_FullRes_AstroToolsProcess.tif].

I think the photo with HLVG applied is better looking than the final photo from StarTools. The StarTools one has some grrenish color in it, while the HLVG filtered one has more blueish colors, closer to the generally accepted colors of the Horshead surrounding region. Of course maybe my processing wasn't done correctly and I might have skipped a step or something. So please, if you want too please feel free to redo my processing and tell me where did I did nmy mistake. The general idea is that in space there is no green color especially on star. There are a few nebulae with a greenish tint but they are rare and is not the case with the Horshead Nebula and surrounding region.

Thank you for sharing the data.
I had a look at the data and images.
Putting the Color module in Max RGB mode (showing channel dominance) reveals very little to no green channel dominance in the StarTools result, which leads me to believe Cap Green is doing its job correctly. If colors still look green, I would recommend trying to calibrate your monitor.

As mentioned before, Cap Green and HLVG are last-resort tools. A dominance of green coloring is almost always a sign of an incorrect color balance.

Looking at the data, it appears it has already been tampered with; there is no bias in the signal and the colors already look "somewhat" balanced. It is hard(er) to tell given the data has been meddled with, but the absence of any yellow suggests some sort of light pollution filter may have been used during acquisition. If so, it will be of course impossible to balance the colors correctly at all (given parts of the spectrum are completely missing). In the latter case, discussing color response becomes a very, very subjective discussion and the presence or absence of green will be more a matter of taste than a mater of objective measurement or science.

Was a LP filter used? How was the data pre-processed?

Thanks!

Yes, light pollution filter was used. Sadly I leave in a heavy light pollution zone and I must use it. I used a CLS-CCD filter.
Pre-processing was done in my usual way: Bias, Dark, Flat, Flat Dark frames (all with the LP filter of course), than basic calibrating and stacking with IRIS without any color balancing.

Anyhow your post had an enlightening effect. And you are absolutely right. I have a problem with my pictures where I use a LP filter ... So there is no universal method to fixing balance on those picture. Maybe a "reverse color correct" for LP filters but than you should make a profile for every single filter that exists out there witch is an impossible task. And that would be still better applied to raw files before stacking I think. So yeah. In this case the whole thing comes down to an artistic preference rather than a scientific correctness. So I must take into consideration when I'm using my LP filter from now on. Thank you, this was a great help for me.

your post had an enlightening effect

That's really good to hear!

Maybe a "reverse color correct" for LP filters but than you should make a profile for every single filter that exists out there witch is an impossible task

The trouble is that we're removing a narrow part of the spectrum, but we are only recording wide bands of the spectrum (red, green and blue). Through color balancing (which operates on red, green and blue wide bands) it's impossible to boost just the missing narrow part of the spectrum without also boosting the spectrum around that narrow part. There is no way of telling which photons that we recorded belonged to the narrow part, and which photons belong to the part around the narrow part - they are all lumped into one reading (red, green or blue).

I hope this explains the problem.

However, there is a way to have a good bit of your cake and eat it too (see here).