IC410. Erratum. Adding HA to LUM actually works just fine.

A place to share images that you have taken with SharpCap.
Forum rules
Please upload large images to photo sharing sites (flickr, etc) rather than trying to upload them as forum attachments.

Please share the equipment used and if possible camera settings to help others.
Post Reply
timh
Posts: 515
Joined: Mon Aug 26, 2019 5:50 pm

IC410. Erratum. Adding HA to LUM actually works just fine.

#1

Post by timh »

I have to fess up. It turns out that I made a pigs ear of adding the HA signal to the RGB luminance in my last post and that is the reason it apparently hadn't worked all that well.

Actually..processed properly ...it looks to me to be the best way to make use of HA data to add nebula detail to RGB without distorting the colours. Anyway to set the record straight and in case folk do use PI (or equivalent steps in other software) and are interested in this technique.

So same data as before.

Skywatcher 200 PDS Newtonian, Baader flattener, F 5.0, CEM70 mount with PDS guiding via AS 120 MM camera and 9 x 50 finder. Pegasus Cube focuser

ASI 294 MM PRO camera, -10C, Optolong 7 nm HA filter
ASI 294 MC PRO camera, - 10C, using an Astronomik UHC filter

Sharpcap livestack captures filtered on FWHM and Brightness, Master darks (33-40 frames) and flats (100 frames) captured in Sharpcap.
124 x 70s (145 min) of RGB at gain 124 and 38 x 3 min (108 min) of HA at gain 124 captured by SC and preprocessed in PI

Same processing steps as before in PI but, crucially, carried out using the pre-stretched non-linear images

1) Process the linear RGB and HA images as normal (fix background (DBE), shrink star morphology, remove green (SCNR), Colour calibration. noise reduction etc.
2) Then stretch both about equivalently using Histogram transformation
3) Then extract the RGB luminance channel and use the Linear function to stretch it to be equivalent to the HA image (now call it say 'RGBLS')
4) Then use the Pixmath max function to create a new luminance image using the function max (HA, RGBLS)
5) Then add the new luminance channel to the RGB image using the LRGB process

Finally curves and anything else to tidy up further

The crucial difference was to apply the process 1) to 5) to non-linear rather than linear images. It also helped to tick the 'reduce chrominance noise' button in LRGB. It just goes to show how important it is to get the processing as well as the capture right!

TimH
Attachments
IC410_NEWT_Baader_070321_RGB_124x70s_gain124_pix_integration_ABE_SCNR_PCCcol_starrmak_PIXMATH_PLUS 38 x 3min HA gain 124 _280221_toLUM_viaLIN_pixmath_MAX_MLT_Trans_curves_curves2_px.jpg
IC410_NEWT_Baader_070321_RGB_124x70s_gain124_pix_integration_ABE_SCNR_PCCcol_starrmak_PIXMATH_PLUS 38 x 3min HA gain 124 _280221_toLUM_viaLIN_pixmath_MAX_MLT_Trans_curves_curves2_px.jpg (430.37 KiB) Viewed 1119 times
User avatar
oopfan
Posts: 1321
Joined: Sat Jul 08, 2017 2:37 pm
Location: New York
Contact:

Re: IC410. Erratum. Adding HA to LUM actually works just fine.

#2

Post by oopfan »

Now we're talkin! Great Job, Tim.

Brian
User avatar
Menno555
Posts: 1053
Joined: Mon Apr 20, 2020 2:19 pm
Location: The Netherlands
Contact:

Re: IC410. Erratum. Adding HA to LUM actually works just fine.

#3

Post by Menno555 »

Wow! Killer image!! :o
And thanx for the description. I don't have PI but nevertheless very useful!

Menno
User avatar
turfpit
Posts: 1779
Joined: Mon Feb 13, 2017 8:13 pm
Location: UK
Contact:

Re: IC410. Erratum. Adding HA to LUM actually works just fine.

#4

Post by turfpit »

Tim

That turned out really well. Thanks for the processing description.

Dave
timh
Posts: 515
Joined: Mon Aug 26, 2019 5:50 pm

Re: IC410. Erratum. Adding HA to LUM actually works just fine.

#5

Post by timh »

Many thanks for the kind comments folks.

Just as a point of possible further interest I also tried further gilding the lily by feeding in a small amount (~ 15%) of he HA signal into the red channel and somewhat more (35%) of an O3 signal (which was much weaker even after compiling 3h of subs) into the green and blue channels. It 'worked' in the sense that the image now showed up HA areas as a deeper red and the middle of the nebula was more blue green. But it didn't seem to be doable without deterioration in the quality of the image --with stars looking less well resolved and overblown etc - and it really didn't add all that much to the original image where the O3/ HA areas of the nebula are already quite well demarcated.

So it probably does help to emphasise the point that less is sometimes more...and that there is not always benefit in adding narrowband data just because you have it. I am beginning to think that my O3 filter won't see much use except on planetary nebulae and supernova remnants?

TimH
Post Reply