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Why not collect HAlpha instead of Luminosity?

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#1 jerryyyyy

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Posted 27 March 2013 - 03:45 PM

Reading a couple posts on the great Whale Galaxy images below and a few others it came to me as a new CCD imager, why not collect Halpha instead of Luminosity (Clear filter). Most Luminosity must be HA anyway and this narrow-band would cut through my horrible light polution.

Must be a downside somewhere... :question:

#2 broca

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Posted 27 March 2013 - 04:19 PM

This is what I was doing when imaging nebula Ha RGB. Galaxies need LUM to make the galaxy luminous, the Ha adds extra punch in the Ha regions of a galaxy.

#3 jerryyyyy

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Posted 27 March 2013 - 04:36 PM

Thanks. :bow:

How do you stack the images? Do you add a HA sub to a R,G or B stack? Or do you do this with layers in Photoshop?

#4 broca

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Posted 27 March 2013 - 05:26 PM

With my current skill set I use the Starizona method outlined here.

#5 vpcirc

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Posted 27 March 2013 - 06:29 PM

Ha, when used as a luminosity frame is a color killer. Ha should be blended very carefully from what I've been taught.

#6 elbee

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Posted 27 March 2013 - 06:34 PM

i would say that "most luminosity" is NOT narrow band. a luminosity filter passes all wavelengths from Blue to Green to Red, blocking UV and IR. if you want to use H-a only you have to be willing to give up the light/detail coming from most of the entire visible light spectrum (~400-700nm wavelength). H-a works great on (most) Nebulae since they emit (a lot of) light in a specific wavelength (~656nm), but that is just a small part of the visible spectrum.

Here is an informative view of the visible light spectrum on:
Jerry Lodriguss' Web Page

the effect of "Luminosity" on color can be quite dramatic. In addition to describing color by RGB values, it can be mapped to HSL values (hue, saturation, lightness). with "missing" lightness data, you may be quite surprised by the result. Turning oranges into chocolate...

Posted Image

using Ha to enhance data can be useful, but it is usually not a substitute for real data across the visible spectrum (unless you just want to make stuff up which is easy to do in Photo processing :)

#7 Rick J

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Posted 27 March 2013 - 06:59 PM

See my comment in this thread:
www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5760045/
for better (and cheaper in time and money) ways to deal with LP when imaging galaxies.

Rick

#8 jerryyyyy

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Posted 28 March 2013 - 09:50 AM

With my current skill set I use the Starizona method outlined here.


Thanks... this looks like somehing I can follow to get started. I now see the downside(s).

#9 Peter in Reno

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Posted 28 March 2013 - 10:27 AM

I've tried that and it's not fun or easy to do.

Have you tried PixInsight? Somebody wrote a very cool script to add Ha to RGB. The script extracts Red channel from RGB image and processes Ha with Red and recombines HaR with GB into HaRGB. I use this script to process HaRGB of M82 without using Luminance and it turned out better than I expected.

M82 in HaRGB

Mixing Luminance with high light pollution don't always work well together but it's doable. I am still working on adding Luminance to HaRGB of M82 and getting there. I am not giving up. I experimented by taking different sub-exposures of Luminance and determine the maximum sub-exposure time for my light pollution condition and in my area it looks like it's about 5 minutes per sub with my high sensitivity Atik 460EX mono camera. Then maybe increase 50-100% sub-exposure times for RGB for same unbinned 1x1. Binning 2x2 or greater is not good for heavy light pollution.

You will also see L(HaR)GB (Luminance channel added to (HaR)GB) at my web site but it was done incorrectly. The color balance is off and M82 as well as the stars are too blue. Like I said before, I am getting there and when I am done processing L(HaR)GB, I will replace the bluish M82 with a more correct color balanced M82 in L(HaR)GB.

I personally don't like Light Pollution Suppression filter. I have IDAS LP2. I started this hobby with SXVR-M25C with IDAS LP2 and I thought it worked well. By the time I became more serious, I started to notice many images have star colors too blue. LPS filter can cause mis-balanced colors so I started imaging without LPS filter and use PixInsight to take care of gradients and it worked much better.

So my bottom line is short sub-exposures and longer total integration times for light pollution. Fof NarrowBand imaging, it does not seem to matter because NB filters do a great job blocking light pollution. I've gone as long as 30 minutes without issues. This will depend on how well your mount can handle long sub-exposure times.

Peter

#10 blueman

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Posted 28 March 2013 - 12:02 PM

I also found that Ha just ruins color when used as Luminance.
It can be used as a blend with Red and Blue channels, but it can be difficult to get the ration right.70% Ha + red and 30% Ha + blue is the recommended starting point.

I no longer am taking luminance for my RGB images. I make synthetic Luminace from the RGB. I find this same a lot of time and has the desired effect.

Blueman

#11 Peter in Reno

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Posted 29 March 2013 - 04:11 PM

Hello,

It turns out that processing Luminance channel from heavy light pollution is next to impossible. If the quality of Luminance channel is not as good as RGB or HaRGB, then it's not worth combining Luminance with RGB or HaRGB. I have found that extracting Luminance from RGB or HaRGB as pseudo-Luminance to be quite effective.

I have uploaded my final process of M82 containing HaRGB combined with pseudo-Luminace of M82.

M82 in HaRGB with Psuedo-Luminance

Peter

#12 alpal

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Posted 29 March 2013 - 05:54 PM

What about using an anti light pollution filter when taking luminance?

#13 Peter in Reno

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Posted 29 March 2013 - 07:17 PM

I have IDAS LP2 Light Pollution Suppression (LPS) Filter and I found that color balancing is difficult. It makes stars look little too bluish. When I stopped using IDAS LP2 and rely on PixInsight removing gradients, I get better results.

LPS is not a miracle filter that wipes out all light pollution and let in all DSO signals. It does not work that way. The problem with LPS is that it blocks some relevant light which may be part of light pollution but it also can cause color imbalance.

Personally, I do not like light pollution filter.

Peter

#14 alpal

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Posted 29 March 2013 - 08:54 PM

Yes Peter,
my Astronomic CLS CCD 2" ALP filter does tend to give a blue tinge to everything
but I've never tried it with my mono camera.

I have a feeling I may be able map the colours slightly different to the standard RGB to improve the balance.

At the moment I just merge the RGB channels but if I assigned them a different angle I may get a good result?

#15 Peter in Reno

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Posted 29 March 2013 - 09:58 PM

Hi Allen,

I am not sure if you are asking me or the community. I do not quite understand your last sentence regarding to "different angle". Without LPS filter, it allowed me to expose shorter sub-exposures and longer total integration times and I think the results are better than with LPS filter.

Peter

#16 alpal

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Posted 29 March 2013 - 10:16 PM

Hi Peter - colours are assigned angles in Photoshop.

Red is 0°
Green is 120°
Blue is 240°


See here:
Clipping Masks and Color Mapping for Narrowband Processing

at

http://www.imagingde...sentations.html

#17 jerryyyyy

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Posted 30 March 2013 - 01:25 PM

Am learning a lot from this discussion. Any idea where I can find the PixInsight plug-in referred to above.

Looking at my subs I do not think the LP is so bad that the L signal would not add to the RGB channels.

#18 Peter in Reno

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Posted 30 March 2013 - 03:14 PM

I got the PixInsight script about adding Ha to RGB image from PixInsight forum at:

http://pixinsight.co...g31975#msg31975

Download "HaRGBCombinationV1.4.zip" from Ioannis Ioannou post. It took me a while to figure out how to add this script to be part of PixInsight. It was not intuitive. I tried many different ways to install the script but once I got it working, I don't recall what I did. It might be best to join PixInsight forum and ask there.

This script is based on Harry's "Adding Ha to a Galaxy" PixInsight video tutorial:

http://www.harrysast...m/Hagalaxy.html

The script simply made our lives much easier. All you have to do is fill in the parameters and the script will do all calculations and output a HaRGB image.

Ever since I received my Atik 460EX mono camera, I've imaged only two DSOs and both contain good amount of Ha: Bubble Nebula and M82 Cigar Galaxy. So far I have not yet image an DSO that does not contain any Ha. Since M82 contained Ha and I captured this image with Ha filter, I can see why adding Luminance to HaRGB may not work well. My Luminance of M82 didn't contain much colorful red star burst at the core like Ha filter did and adding Luminance image to HaRGB just made it worse. Same thing for Bubble Nebula, my HaRGB looks better than L(HaR)GB.

Maybe if I image an DSO that does not contain Ha, then adding Luminance to RGB may just work well and better than RGB alone.

Anyone else have experience with adding Luminance to HaRGB and made the result better than not including Luminance for HaRGB? If so, please show us your samples.

Peter

#19 Peter in Reno

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Posted 30 March 2013 - 03:49 PM

I think I found a procedure to add script to PixInsight:

http://pixinsight.co...g30421#msg30421

1) download the script (*.js) and save it to folder C:\Program Files\PixInsight\src\scripts
2) run PI
3) select menu/SCRIPT/Feature Scripts
4) press add button, select "scripts" or where tha HaRGBCombination.js file is located, click on "Select Folder" button; and you will find the new script in the list called "HaRGBCombination"...
5) Click on "Regenerate" button.

Open Ha and already combined RGB files and run SCRIPT->Utlities->HaRGBCombination script. Hopefully a new window will pop up and you fill in the parameters.

My OS is Windows 7 64 bits so the location to place the script may be different than yours if you use different Windows than mine.

I am not an expert about this script. Please follow Harry's "Adding Ha to a Galaxy" video tutorial and it should give you clues about the parameters to fill in the script.

Peter

#20 jerryyyyy

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Posted 30 March 2013 - 11:12 PM

Thanks. Believe it or not I found the script, loaded it, it runs and have an RGB and Ha files loaded.

I get an error:

line 129: Error: GenericImage::Allocate(): Insufficient number of channels

For the record, there is apparently a newer version is out somewhere. This one has an error in line 128 true should be false.

In any case it is coming up OK post-editing and will report my adventures.

#21 Peter in Reno

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Posted 30 March 2013 - 11:19 PM

Hi Jerry,

I forgot to mention that if you are using latest PixInsight version 1.8 Release Candidate 1 - 5 or RC1 - RC5, you need to edit the script as shown in this link:

http://pixinsight.co...g35224#msg35224

I am using PixInsight 1.8 RC5.

In order for the script to work, you must first open two FIT files: Ha and combined RGB files and then execute the script.

Peter

#22 jerryyyyy

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Posted 31 March 2013 - 06:40 PM

Thanks,

I got the script error fixed and ran the program. I have data in the can on M97... so now I have a very nice pink M97 :). Seriously, it works and I can see how I can dial back the H-alpha. Funny how when I put it next to the RGB images it really punches out... strongly. I originally collected Ha and O-III on M97, but then saw most people used RGB to get the colors. Now I guess I can combine them both if I can learn how to use this software correctly.

Seems that the Ha overwhelms the blue in the center... as well as adding red to the outside.

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