Hello dear Astropeeps, I am still rather new to the SHO palette with a mono-camera and I just completed my third image on the North American Nebula and never collected as much data for an image as of now. I love to see the separation of gases and how the interaction of different colors create different new combinations such as the SII and OIII interactions create magenta patches. I also take great care to calibrate and balance the intensity between the channels and as a result there are also parts of the image that are green from the H-Alpha. I intentionally left those areas untouched, because a.) I like how it looks like (we collect a whole third channel to introduce more color, why get rid of) and b.) it feels unscientifical to run SCNR to get rid of it. My question to you is: What is your approach with the SHO palette? Do you leave the green in or not? I am also more than open to hear (constructive) criticism towards my processing and hear your opinion on my latest image. CS, David
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Hello David,
Once I used to do just that, to wipe out all of the green in the photos because I was literated by Astrobin and Youtube astrophotographers to do so.. After I read "Picturing the Cosmos, Hubble Space Telescope Images and the Astronomical Sublime" I've started to understood that maybe my processing should have a little of green. Not to much, but a little bit, despite the green color not been a present color in the universe, or at least in most of the universe as we know it. And this why I started to reconfigure my processing. I leave a bit of green there just to give a more natural SHO palette.
Once I saw a video from Dylan O'Donnel regarding the faking of SHO palette and removing the green we are only working with a bicolor image, meaning Red and Blue information and eliminating the green channel while removing the green from an image.
I don't agree on this with him, because one thing is removing the green channel and you will never ever have a color image, just a BW one, and the other is keep the green channel but removing the green from the color mixing by the 3 channels (Red, Green and Blue). Those are two completely different things.
Best regards,
Cesar
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For me it depends on the target. I have an image of the Horsehead region that I left the green in and worked on separating the colours as much as possible, and I like it. IMO, we are doing art as much as science and interpretation is up to the astrophotographer. Some might gripe about certain palettes or interpretations, but in the end it is your work to do as you please. If we all keep doing the same thing, the same way, then all our images will look the same. Narrowband imaging to me is powerful because there’s literally no end to combinations and that’s what makes it fun. We can’t see any of these objects with the naked eye(at least compared to what they look like from our cameras), so what it “should” look like is a moot point.
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Interesting discussion, and I will usually develop the same target along several lines, including ones that preserve the green signal. Rather than SCNR, I will usually turn to Narrowband Normalization to modify the green but without losing the signal. @Bill Blanshan and @Mike Cranfield have developed a great tool for this, and it has several useful modifications you can preview in real time.
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I’m on the same line as @ScottF & @Rob Foster in that it depends on the target as well as what I’m attempting to do with it. My last image that I shot I actually used the HSO pallet and found I liked it a lot. You can see it here if your interested: https://www.astrobin.com/uqfj83/D/In the past I struggled to get the colors the way I wanted and found that HSO color pallet to be a better way (at least for me) to incorporate the green channel in my images.
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I generally use SCNR to reduce the green by 50% - 80% — almost never 100%. Some level of green maintains the orange tones and provides a much richer color palette than if you remove 100% of the green, which results in almost pure yellow/blue tones. Still, I generally don’t want to see anything in the image that looks pure green.
John
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I do the same as what John does. The colors are richer if a bit of green is left in.
A related question is - how do people normalize the individual masters? I find that the choice of which master to serve as the reference for linear bit prior to combination has a large effect on the final color. Is there a logical way to do this?
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Here is my horsehead that I just posted(if I've linked it correctly). The colours are a bit wild, but that's what I like about NB, you can do so many combinations. I like how different parts of the nebula are different colours. It's not everyone's cup of tea, but I like experimenting. https://astrob.in/ncubja/0/ |
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Agree with everyone on it depends on the target. I'm personally not a fan of SCNR in anything but tiny doses. The thought being if I wanted a bicolor image I should have just taken one to start with. I blend Ha into both red and green channels most of the time to get the color I like. There are many ways to do this in both Photoshop and Pixinsight that I use.
CS,
Jeff
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I always leave a touch of green and magenta in my blends. I think it tells the story better.
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I just imaged the Eastern Veil Nebula with narrow band filters. I processed it with RGB = HSO first. I didn't alter the balance of the colors in processing because there was little green as there was little sulfur. I then processed it with RGB = SHO and upped the red and blue channels until I liked what I saw. Wherever there is only hydrogen, there is some green. Where there was a mix, there is yellow and cyan. I prefer this image to the HSO one, but both have their charms. I just uploaded the SHO version as my first AstroBin post: https://astrob.in/9vvmlw/0/ |
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I think one thing you have to keep in mind, beyond the aesthetic of the colors, is that using SCNR to remove green is also removing the highest SNR information you have captured: the Hydrogen data. There are many ways to balance the color contributions of the Hydrogen so that you end up with an image made up of many hues and not dominated by green. SCNR is not one that I use. But I do I try to be aware of what I'm doing to the Luminance contribution of the H channel and thus to the SNR.
The solution here is to do one thing with the Color data and another with the Luminance data. I typically create a PsuedoLuminance of either 1/3 each H,S, and O or some other mix that leans a bit more on the strongest channel. That frees me to be more aggressive with the color data to get the color mix I like.
You have to be careful not to "strand" color data. By that I mean having some feature in the Color data that is not supported by a structure in the Luminance data. This is the main issue with using H alone for Luminance. You get great SNR and detail that way but you can have blue structures that are just featureless blobs of blue.
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I agree with Kevin above, I never use SCNR on SHO data, only RGB. I also like to leave a little green which I think looks better to me than removing all of it in SHO. I usually use PI or PS to transform the green signal to either yellow by reducing cyan or blue by reducing green and playing with it in stages and experimenting to see what looks best.
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Similar to Kevin's approach, lately I've been using an extracted luminance from an SHO blend, and applying it to my own HSO formula to maintain all the details. Sometimes the Oiii details get lost, so I'll use pixelmath to blend the Oiii layer back in on top of my HSO.
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Like others have mentioned, if you nuke all the green with scnr you'll end up with a bi-color image. Leaving some green in there, even if you dont see pure green helps with the other colors.
I like green and tend to leave some visible green in place. To my eye it makes for a nice transition of different colors, similar how in certain conditions you can pick up a faint green band at sunsets.
As for science… we're just making pretty pictures. NB in mu opinion does allow for a little creativity in the colors.
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Hi David,
Generally I nuke it out, but on some targets I don't. The answer "it depends" is generally non-informative, a way of not giving a definite answer because the questionner wants to know what does it depend on.
There seems to be a theory or critical attitude towards the SHO palette that decrees that since you use a 3 filter composition, you should see green in the image. This is baseless. The final colors in the image are a composition of the 3 filters anyway, so all 3 participate. It's also false that if you take out the green, you will end up with a bichrome image. You can end up with browns, yellows, reds, magenta, blues etc. It's true that if you completely take out green in the image, you will delete all cyan or turquoise nuances.
Besides the obvious aesthetic preferences, some scientific arguments can be given for reducing green in images.
The first one is based on human vision: our color-sensitive retinal cells are most sensitive to green. This is why camera captors are also very sensitive to green, imitating human vision. The maximal sensitivity of our photopic vision is at 555 nm wavelength, green/yellow. Pretty much why the life vest in your car is green/yellow and why we usually use green/yellow markers to underline our texts when preparing an exam.
The second one is based on the structure of the universe, which we all know is dominated by Hydrogen. Most emission nebulae emit heavily in Ha, the SHO composition will be dominated by and look very green.
When we combine these two premises, it becomes clear why green should be reduced and can be reduced completely sometimes. The goal of the false color Hubble palette is to make it possible for the human eye to distinguish the structures in these emission nebulae. The L information is not lost when we manipulate the color palette (when you compensate for the intensity decrease of course). The green dominance however produces a veil since Ha is present all over the place. You cannot see any chromatic contrast, since whenever the green dominantes in adjacent structure, your eye will be more sensitive to G than the other colors seen in the image. When you decrease it, the subtle color differences magically appear. The Ha in the palette is still there, for example in the yellow clouds. Yellow is made up of R and G, no blue: (255,255,0) for pure Y. If you do not reduce green to match the red intensity in those clouds, you'll never obtain yellow. But the Ha or the G contribution has not disappeared, it's intensity is more proportionate to the R.
However, you can go too far when you take out green, when the chromatic contrast disappears in the respective structure and you no longer see the subtle differences present before.
So, I think there is a bit more to be discussed than just "that's the way I like it". There are more subtle and precise ways of taking out the green than SCNR though.
Clear skies,
Bogdan
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try a colorized SHO palate. It's much superior to standard Hubble palate. As a suggestion, my latest image I uploaded a couple of hours ago used gold for Ha, Rusty red for S and teal for O. Give it a try…it's very pleasant
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No I do not I think one thing folks forget is that when you wipe out green you don’t eliminate green you eliminate greens effect on other colors. You need RG and B to get the full pallet so what you end up with and I see it all the time is a blue and orange image.
Once you linear fit and know how to manipulate and massage the colors a bit in PS you can create almost the entire color pallet in SHO and use the green to your advantage. The key is to not allow the Ha to overwhelm the image and linear fit is a bit help there.
Green allows for so many more subtle colors and smoother transition between colors and u think early on many of us just nuked it but once you understand processing and color theory better you can definitely use green to your advantage.
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Ryan:
Once you linear fit and know how to manipulate and massage the colors a bit in PS you can create almost the entire color pallet in SHO and use the green to your advantage. The key is to not allow the Ha to overwhelm the image and linear fit is a bit help there. I consider myself fairly good at PixInsight but have not bothered to learn Photoshop beyond basic curves adjustments which are superior to what PI provides. It is obvious that some of the really nice narrowband images are photoshop color adjustments. I'd like to add these to my toolbox so I am not limited by PixInsight. There are any number of suggestions for PI tutorials. Are there similar PS tutorials from an astrophotography standpoint? I am mainly interested in color manipulation.
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Ryan:
No I do not I think one thing folks forget is that when you wipe out green you don’t eliminate green you eliminate greens effect on other colors. You need RG and B to get the full pallet so what you end up with and I see it all the time is a blue and orange image.
Once you linear fit and know how to manipulate and massage the colors a bit in PS you can create almost the entire color pallet in SHO and use the green to your advantage. The key is to not allow the Ha to overwhelm the image and linear fit is a bit help there.
Green allows for so many more subtle colors and smoother transition between colors and u think early on many of us just nuked it but once you understand processing and color theory better you can definitely use green to your advantage. Hello dear Astropeeps,
I am still rather new to the SHO palette with a mono-camera and I just completed my third image on the North American Nebula and never collected as much data for an image as of now. I love to see the separation of gases and how the interaction of different colors create different new combinations such as the SII and OIII interactions create magenta patches.
I also take great care to calibrate and balance the intensity between the channels and as a result there are also parts of the image that are green from the H-Alpha. I intentionally left those areas untouched, because
a.) I like how it looks like (we collect a whole third channel to introduce more color, why get rid of) and
b.) it feels unscientifical to run SCNR to get rid of it.
My question to you is: What is your approach with the SHO palette? Do you leave the green in or not?
I am also more than open to hear (constructive) criticism towards my processing and hear your opinion on my latest image.
CS,
David I am not a fan of leaving the green in an SHO image. It seems to be a new trend but it can really overwhelm the image if you are not careful.
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How many hubble SHO images don't have green in them? and why would we want to attenuate the hydrogen out of the image?
I guess it really depends on what you're trying to achieve with your image. If you're going for 'pretty picture' then, do what you like… If you're trying to specifically highlight the different gasses that make up a nebula, then why would you cut out the green?
I would always leave the green in an image, would I scale the green to be less extreme in some cases - of course, but I would never drop it out to be significantly less than SII or OIII, unless the target I was imaging was composed that way….
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Franco Rodriguez:
try a colorized SHO palate. It's much superior to standard Hubble palate. As a suggestion, my latest image I uploaded a couple of hours ago used gold for Ha, Rusty red for S and teal for O. Give it a try...it's very pleasant THIS....... I tried colourising my SHO image of the Fighting Dragons!! I'm happy with the current revision but have since doubled my initial total data so going to do another revision!! I did struggle trying to initially balance the Ha, S and O channels when I colorised. Didn't quite get gold, rusty red and teal but this process IMO is very in depth and you do have a lot of control/input which is really fun
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Alex Nicholas:
How many hubble SHO images don't have green in them? and why would we want to attenuate the hydrogen out of the image?
I guess it really depends on what you're trying to achieve with your image. If you're going for 'pretty picture' then, do what you like... If you're trying to specifically highlight the different gasses that make up a nebula, then why would you cut out the green?
I would always leave the green in an image, would I scale the green to be less extreme in some cases - of course, but I would never drop it out to be significantly less than SII or OIII, unless the target I was imaging was composed that way.... Hi Alex, Well, a lot of iconic Hubble images do not have green in them. Here are some examples: I don't believe that the Hubble team is cutting signal out by reducing or "zapping" the green, or that they don't know what they're doing. This is pretty much contrary to the idea that if the Hubble palette uses 3 filters, you have to leave green in the image, if not it becomes a bicolor image etc. Of course there is an aesthetic criterion involved. Some astrophotographers on astrobin are really good at keeping the green in the image with nice results, some images look best without it imo. Everyone is free to keep it or clear it as they like, but there is no obligation for it to be present in the Hubble palette. CS, Bogdan
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Sam Badcock:
Franco Rodriguez:
try a colorized SHO palate. It's much superior to standard Hubble palate. As a suggestion, my latest image I uploaded a couple of hours ago used gold for Ha, Rusty red for S and teal for O. Give it a try...it's very pleasant
THIS....... I tried colourising my SHO image of the Fighting Dragons!! I'm happy with the current revision but have since doubled my initial total data so going to do another revision!! I did struggle trying to initially balance the Ha, S and O channels when I colorised. Didn't quite get gold, rusty red and teal but this process IMO is very in depth and you do have a lot of control/input which is really fun I prefer using Bill Blanshan’s Narrowband Normalization process. As long as you do not over process the image prior to using the process. For this I just used channel combination, background neutralization and unlinked stretch prior to NN. Then color masks and curves. https://astrob.in/djbgde/0/ |
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Sam Badcock:
Franco Rodriguez:
try a colorized SHO palate. It's much superior to standard Hubble palate. As a suggestion, my latest image I uploaded a couple of hours ago used gold for Ha, Rusty red for S and teal for O. Give it a try...it's very pleasant
THIS....... I tried colourising my SHO image of the Fighting Dragons!! I'm happy with the current revision but have since doubled my initial total data so going to do another revision!! I did struggle trying to initially balance the Ha, S and O channels when I colorised. Didn't quite get gold, rusty red and teal but this process IMO is very in depth and you do have a lot of control/input which is really fun
I prefer using Bill Blanshan’s Narrowband Normalization process. As long as you do not over process the image prior to using the process. For this I just used channel combination, background neutralization and unlinked stretch prior to NN. Then color masks and curves.
https://astrob.in/djbgde/0/
I’ve used narrowband normalisation as well!! Amazing script, I love it!! I also enjoy the extra work involved by colourising the images before combining them!! For me it’s a bit more “fun” LOL
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