Author Topic: H-Alpha Tutorial or Example  (Read 4751 times)

Offline greeko

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H-Alpha Tutorial or Example
« on: 2009 November 26 06:41:17 »
Hi PixInsight users

I've currently switched to a monochip CCD and now acquiring more H-Alpha data.
Any previous H-alpha data I would combine in Photoshop after splitting OSC images RGB channels and copying and pasting H-alpha to Red channel.

Is there a good tutorial or module which will allow me to handle this function within PIxInsight as I'm trying to eliminate Photoshop all together.
I did search the forums and found a thread posted in 2008 however this description provided is not very intuitive.

Thanks in advance
Troy

Offline Nocturnal

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Re: H-Alpha Tutorial or Example
« Reply #1 on: 2009 November 26 07:37:48 »
Hi,

load your OSC image and use Image->extract->split rgb channels to, well, split your RGB channels. Then recombine as you want with your Ha data with the Processes->ColorSpaces->ChannelCombination process.
Best,

    Sander
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Offline Niall Saunders

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Re: H-Alpha Tutorial or Example
« Reply #2 on: 2009 November 26 08:12:31 »
Quote
recombine as you want with your Ha data
Sander, Troy,

I am very much ready to do the same thing now, after recently moving back from my DSI-IIC to the DSI-IIP.

I haven't finished calibrating and aligning my first set of data, but I visualise my workflow involving some sort of 'multiplicative' combination of the Ha and Rd data, prior to recombination using ChannelCombination (with or without using a Lum channel as well, either 'true' Lu, or 'synthetic' Lu by using the Ha data again.

Am I on the right lines here? Does this suggestion help you at all, Troy?

Cheers,
Cheers,
Niall Saunders
Clinterty Observatories
Aberdeen, UK

Altair Astro GSO 10" f/8 Ritchey Chr├ętien CF OTA on EQ8 mount with homebrew 3D Balance and Pier
Moonfish ED80 APO & Celestron Omni XLT 120
QHY10 CCD & QHY5L-II Colour
9mm TS-OAG and Meade DSI-IIC

Offline Nocturnal

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Re: H-Alpha Tutorial or Example
« Reply #3 on: 2009 November 26 08:46:52 »
Hi Niall,

there was a thread about this subject a few months ago where someone did all kinds of combinations to find out what worked 'best'. Personally I'm not convinced Ha and RGB should be mixed at all. The best ones are hard to distinguish from plain RGB and the other ones look worse. In other words I don't consider it worth the effort. But that's just me and of course you should not listen to that at all :) Please prove me wrong by showing an Ha+RGB image that looks better than the original RGB.

The best combinations I've seen so far did what Troy asked about, replacing R with Ha for an HaGB image. Clearly when using line filters it's an easy choice to decide between an R or Ha filter and it doesn't 'cost' anything to do so. When shooting OSC you have to make a decision between adding more OSC data vs. putting an Ha filter in there and shooting Ha instead. I think the extra exposure time is better spent shooting more OSC data.
Best,

    Sander
---
Edge HD 1100
QHY-8 for imaging, IMG0H mono for guiding, video cameras for occulations
ASI224, QHY5L-IIc
HyperStar3
WO-M110ED+FR-III/TRF-2008
Takahashi EM-400
PIxInsight, DeepSkyStacker, PHD, Nebulosity

Offline Niall Saunders

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Re: H-Alpha Tutorial or Example
« Reply #4 on: 2009 November 26 08:54:34 »
Quote
you should not listen to that at all

No Sander, your advice is quite readily accepted - I'll try things boths ways, although I didn't get nearly enough Ha data (10 minute exposures) first time out, so that data set still has quite a bit of residual background noise.

What about creating a 'colour' image that uses Ha only - in other words an 'all red' image - is it my imagination playing tricks on me, or does that get done? If it does (empty G and B channels, and Ha substitued into the Rd channel), then are the 'stars' just left 'red' as well?

Cheers,
Cheers,
Niall Saunders
Clinterty Observatories
Aberdeen, UK

Altair Astro GSO 10" f/8 Ritchey Chr├ętien CF OTA on EQ8 mount with homebrew 3D Balance and Pier
Moonfish ED80 APO & Celestron Omni XLT 120
QHY10 CCD & QHY5L-II Colour
9mm TS-OAG and Meade DSI-IIC

Offline Nocturnal

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Re: H-Alpha Tutorial or Example
« Reply #5 on: 2009 November 26 08:59:48 »
Niall,

there's no conceptual difference between a monochrome image and one that puts the same data into one or more channels of an RGB image. Personally I like monochrome Ha images quite a bit. They're a bit Ansel-esque.

When you start combining channels from different sources (Ha and OSC data) keep in mind that the lowest SNR will dominate. So try to keep the SNR similar. Sticking a low SNR Ha on an RGB image as Luminance will trash a picture for example.

I should add that I think combining Ha with other NB images (say Hubble palette) is definitely worth the trouble but there too you need similar SNR.
Best,

    Sander
---
Edge HD 1100
QHY-8 for imaging, IMG0H mono for guiding, video cameras for occulations
ASI224, QHY5L-IIc
HyperStar3
WO-M110ED+FR-III/TRF-2008
Takahashi EM-400
PIxInsight, DeepSkyStacker, PHD, Nebulosity

Offline greeko

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Re: H-Alpha Tutorial or Example
« Reply #6 on: 2009 November 26 10:36:51 »
Hi Sander and  Niall

Thanks for the feedback Sander.
Just to be clear I'm only using a monochip CCD for data acquisition and was just pointing out that I previously had a OSC CCD and could easily combine the H-alpha data by copying and pasting this into the red channel via Photoshop.

I've been working with the LRGB module which is really brilliant
As silly as this sounds I have not found a way to simply copy and paste within PIxInsight.
I do realize dragging and dropping one image to another creates a mask but not clear if this is considered an actually combination of the channels.
Its not obvious when viewing an image .

If select copy, paste flatten layers is an option like in Photoshop this would be helpful.

Niall
To address your question I think the method to be used for blending H-Alpha data will depend on a couple things.

First is the object being imaged and how much H-Alpha signal is emitted; I feel this determines whether a combine option or simply replace the red channel is used.

Second the end users look and feel of the image when its completed.
Point is I dont think there is one clear cut dry method .
My feeling is the method used will vary.

I always use both methods and chose to display the one which is most appealing to me.
Troy

Offline Nocturnal

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Re: H-Alpha Tutorial or Example
« Reply #7 on: 2009 November 26 10:45:08 »
Troy,

there is no layer concept in PI so the copy/paste paradigm from PS is meaningless. Masking in PI does not combine chanels at all. Perhaps you should experiment a little with it to gain a better understanding of the feature. Try applying a luminance mask to an image and then adjust the saturation with a curve for example. Bright areas get more adjustment than dim areas.

Maybe you can explain further how you want to use copy/paste? I've not missed it yet. It seems that when you understand the LRGB module like you said then you're all set, right?



Best,

    Sander
---
Edge HD 1100
QHY-8 for imaging, IMG0H mono for guiding, video cameras for occulations
ASI224, QHY5L-IIc
HyperStar3
WO-M110ED+FR-III/TRF-2008
Takahashi EM-400
PIxInsight, DeepSkyStacker, PHD, Nebulosity