Ngc6744

[Asterix2020]

Had a great time at Astrofest, and with some help from some generous people I was able to sort out the new equipment and get some images.

NGC6744 taken over 2 nights, total of 320 minutes. 10 min subs. GSO RC8, TSOAG9, NEQ6 and CDS-600D DSLR.

Larger version here: http://www.astrobin.com/full/109660/0/

Final version: http://www.astrobin.com/full/109660/B/

[RickS]

Also a nice one...

[cometcatcher]

Very nice. I'm contemplating an RC8 for small galaxies like this.

[troypiggo]

Lovely image. Does it look a little magenta to you? Maybe the white balance needs tweaking?

[Asterix2020]

Yes, I thought the background was a bit magenta, but when I tried to remove that in Startools, it made the galaxy core green. As it is, I used Lightroom and a mask to leave the galaxy untouched and alter the background to less magenta. I think I will get more data on this galaxy from home since it's already a good start, so I won't spend too much time on the colour for this version.

Open to suggestions on how else I could remove the magenta though.

[troypiggo]

Depends on your software. PixInsight you'd do a background neutralisation and colour calibration pretty easy. If you post your untouched images we can have a play.

[Spookyer]

Good one Paul, nice to see you got some good data.

Brett

[Asterix2020]

Thanks Kevin, Rick and Brett.

Troy, what data do you want? The FITS file out of DSS is 200MB. Is this what you need?

[troypiggo]

I'm not sure what DSS does to images, but it's a starting point :)

[Asterix2020]

This is my stacked DSS FITS file. It should be as untouched as I can make it.

https://onedrive.live.com/redir?resid=6EE8C56E7DD871A7!503&authkey=!AHTdQh6Yx7fbAh0&ithint=folder%2cFTS

[jjjnettie]

:) Nice one Paul. :)

[irwjager]

Hi Paul,

I had a look at the data set in StarTools. I actually couldn't produce the magenta cast - any chance you could share your workflow with us, so we might pinpoint what caused it?

What I did notice though was that the data has been pre-colorbalanced. This introduces anomalous colour in the highlights (because colour balancing necessitates clipping). DSS does not seem to respect settings telling it to keep its hands off the colour data as recorded :( As a work around, you could use dcraw from the command line (see correct parameters elsewhere).

Another thing I noticed were some dust donuts that were not corrected by your flats.

The image you posted is indeed a little on the blue side. However, this image should be really easy to color balance in fact; it is a milkyway type galaxy, its aggregate pixels being a good whitebalance source. Add to that a nice evenly distributed star field (in terms of temperatures) and the whole image becomes the perfect calibration source! (marred only a by DSS butchering the colour information in the highlights)

What you'd be looking for in terms of this image and NGC6744 are (as mentioned) a good even distribution of all star temperatures from red->orange->yellow to white and blue, and, in terms of the galaxy, a bluer outer rim (younger stars due to more star formation), a yellow core (older stars due to less star formation) and the presence of HII areas/knots (predominantly emitting on the Ha and Hb wavelengths which turns up a purplish/pinkish colour). Evidence of the latter is visible, but it's not much.
This is all assuming you care about your colour information conveying interesting information to the viewer of course :) If you want to stretch and mangle your colour information along with your luminance (like most people/software) all bets are off of course...

All this is also assuming that all you're capturing is the visible wavelengths. Since your camera has a modified spectrum (correct?) you will be capturing more red and below, though I cannot immediately see evidence of increased sensitivity.

Quick result here;
http://www.startools.org/download/TutorialResults/Paul_NGC6744.jpg

[Asterix2020]

Thanks Ivo, I do like your version. I did notice those dust donuts too, I tried to hide them :). I have more flats so I might try and redo it. I did use DCRAW to convert the .CR2 to .tiff as we have previously discussed, so I don't know where DSS is corrupting the colour data. I used median sigma kappa clipping for my stacking parameter, is this the best to use?
Camera is spectrum modified but has a UV/IR blocking filter in place.

[Asterix2020]

Here's my workflow:
tarTools 1.3.5.289
Sun Jul 27 11:57:47 2014
-----------------------------------------------------------
File loaded [E:\Astrophotos\2014-07-25 Astrofest\ngc6744 330 mins.FTS].
---
--- Crop
Parameter [X1] set to [111 pixels]
Parameter [Y1] set to [102 pixels]
Parameter [X2] set to [5009 pixels (-78)]
Parameter [Y2] set to [3221 pixels (-149)]
--- Auto Develop
Parameter [Ignore Fine Detail <] set to [Off]
Parameter [Outside ROI Influence] set to [15 %]
--- 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 [1 pixels]
Parameter [Drop Off Point] set to [100 %]
Parameter [Corner Aggressiveness] set to [100 %]
Parameter [Aggressiveness] set to [75 %]
--- Auto Develop
Parameter [Ignore Fine Detail <] set to [Off]
Parameter [Outside ROI Influence] set to [15 %]
--- Contrast
Parameter [Expose Dark Areas] set to [No]
Parameter [Compensate Gamma] set to [No]
Parameter [Precision] set to [256 x 256 pixels]
Parameter [Dark Anomaly Filter] set to [1 pixels]
Parameter [Aggressiveness] set to [75 %]
Parameter [Dark Anomaly Headroom] set to [15 %]
--- 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 [100 %]
Parameter [Small Detail Bias] set to [75 %]
--- Color
Parameter [Cap Green] set to [To Brown]
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 [2.00]
Parameter [Bright Saturation] set to [Full]
Parameter [Saturation Amount] set to [218 %]
Parameter [Blue Bias Reduce] set to [1.00]
Parameter [Green Bias Reduce] set to [1.57]
Parameter [Red Bias Reduce] set to [1.35]
Parameter [Mask Fuzz] set to [1.0 pixels]
--- Life
Parameter [Detail Preservation] set to [Min Distance to 1/2 Unity]
Parameter [Compositing Algorithm] set to [Power of Inverse]
Parameter [Inherit Brightness, Color] set to [Off]
Parameter [Output Glow Only] set to [No]
Parameter [Airy Disk Sampling] set to [128 x 128 pixels]
Parameter [Airy Disk Radius] set to [8 pixels]
Parameter [Glow Threshold] set to [12 %]
Parameter [Detail Preservation Radius] set to [20.0 pixels]
Parameter [Saturation] set to [50 %]
Parameter [Strength] set to [100 %]
Parameter [Mask Fuzz] set to [1.0 pixels]
--- Develop
Parameter [White Calibration] set to [Use Stars]
Parameter [Gamma] set to [1.00]
Parameter [Skyglow] set to [0 %]
Parameter [Digital Development] set to [Off]
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 [3 %]
Parameter [Dark Anomaly Filter] set to [15.6 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 [0 %]
Parameter [Mask Fuzz] set to [1.0 pixels]
Parameter [Scale Correlation] set to [3]
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 [4.32 %]
Parameter [Smoothness] set to [75 %]
File saved [E:\Astrophotos\2014-07-25 Astrofest\Astrofest\NGC6744 330 mins.tiff].

[Asterix2020]

Ivo, how can I tell if the FTS file is pre-colour balanced? When I enter the colour module, the galaxy goes green with the whole image selected. Removing the green left me with the magenta the first time. I tried masking the galaxy, still green.

[Asterix2020]

Ok, here's the new FTS file, I think the flats made the dust bunny better, but I still get a green colouring on default, and removing the green bias leaves me with magenta/purple.
https://onedrive.live.com/redir?resid=6EE8C56E7DD871A7!510&authkey=!APDkR9KhRODqEoM&ithint=file%2cFTS

[troypiggo]

I had a quick play with the original data you sent. Managed to tidy it up a little with just PixInsight background neutralisation and colour calibration, then boost saturation curve.

The version attached is a little dark. I did a slight histogram stretch after this, but must've saved and uploaded the wrong version. But you get the picture.

[Asterix2020]

The background looks better but the galaxy has no colour now. I thought the galaxy should have blues and reds (nebula) in it?

[troypiggo]

Yes, you're right. That looks rubbish. I think I discarded the one I meant to post, and uploaded an earlier/incomplete version. Because it was a quickie I didn't save any of it. I'll have another crack. The point is, the white balance can be corrected using the right tools :)

[irwjager]

That's really odd, as bias seems to have been removed and light pollution is 'correctly' colored. Typically, non corrected data is a distinct green or teal colour and has a bias. It is as though the DSS settings pertaining to color calibration/alignment are not all set to 'no'.



I can reproduce the magenta background remnant if you keep the data at full resolution and do not counter the dark anomalies (caused by noise) by upping the Dark Anomaly filter in the Wipe module. Contrary to other software, Wipe, by default, takes your data as gospel and refuses to Wipe away anything lighter than the background, which it takes to be the darkest pixel it can find in an area (that's why ST tends to preserve faint nebulosity better). If it cannot rely on per-pixel measurements, but should instead look at averages of clumps pixels, you can tell it to do so with the Dark Anomaly filter.

The attached screenshot should be indicative of what you should be seeing in the Color module upon first launch.



The whole galaxy going green sounds like a bug :mad2:, which, if reproducible I would like to squash immediately. When the galaxy comes out green, does cancelling, binning to 50%, 'Keep'ing that and 'undo' ing the binning (e.g. now you're back where you started), then redoing the Color module give you correct colors?

[troypiggo]

Another go. Blues coming out in the galaxy. Bit hard to see any reds without actual Ha data. Still a bit funky colour-wise, but was more just an exercise to see how we can get rid of that magenta and get the colours back.

[Asterix2020]

With some help from Ivo I've managed to repro this and remove the magenta. So it wasn't the tools it was the person using them :)

Thanks for everyone's help and to Troy reprocessing as well.

Larger version here: http://www.astrobin.com/full/109660/B/

[troypiggo]

Nice.

[tilbrook@rbe.ne]

Really nice job Paul!:thumbsup:

NGC 6744 is difficult to process.

Cheers,

Justin.

[Asterix2020]

Thanks Troy and Justin.

[cometcatcher]

The repo is excellent.

[Asterix2020]

Thanks Kevin.

[astroron]

Very nice Paul,:) you have brought out the bar superbly :D
Cheers:thumbsup:

[andyc]

That's very pleasing to look at, nice image :thumbsup: