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A "Blue" Hidden Galaxy


tomato
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I managed to add another 3.5 hrs data to my IC 342 Hidden Galaxy image last night, albeit with a 70% illuminated moon in attendance.  I added this to the raw data (Esprit 150/IMX 571 OSC sensors) to give 8.4 hrs of integration, then calibrated and stacked in APP. I then applied the APP remove LP and Calibrate Star colours tools before using the StarXTerminator tool in PI to separate the stars (very impressed), reduce these and stretch the starless galaxy image before re-combining for further processing in Affinity Photo.

What is intriguing me is unlike my first image, I appear to have lost a lot of the golden hue commonly seen on images of this galaxy, the spiral arms in particular have  more blue in them  than usually seen. The image also looks odd as the galaxy is in quite a dense star field and my radical star reduction has now made it look like it is in a sparsely populated part of the sky.

Anyway,  I can appreciate the comments made that if this galaxy was in a different part of the sky, it would probably out do M101 or M51 as a fine example of a face on spiral galaxy.

Thanks for looking.

Image03APPSTXAPW.thumb.jpg.96247aca0d7cfee76a9603e509e01702.jpg

 

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Even with star reduction it is obvious that you are oversampled when zoomed in to 100%.

Have you considered binning the data at linear stage - at least x2 but even maybe x3?

Even with x3 bin you'll still have "HD compatible" format of about 1770 x 1100

Second objection is very strange effect around stars. It looks like there is "smooth" halo around all bright stars that is rather distracting:

image.png.54c5b6280efa47ba075b93d2aa6becb8.png

image.png.47e670e0d0bf443eab181da231f4079e.png

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Thanks for the feedback. Yes, it’s imaging at 0.7 arcsec/pixel so binning the data is a good idea, I’ll have to see how best to do this with the software I have available. StarTools has a good binning tool but I need to see if I can save it from there in a linear state.

As for the halos, this might be a artefact of my star reduction technique, and it’s the very first time I have used StarXTerminator, I’ll take a look.

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6 minutes ago, tomato said:

Image binned 60% in Startools, and a less aggressive star reduction in PI. I think the smooth halos are still there but are somewhat less obvious? 

Yes, stars look better now.

Background is a bit lighter in this version? I think I slightly prefer original background.

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Here is one more, binned 35% in Startools, and a darker background. Halos have gone, but the background is noisier.  Again, thanks for the feedback, I now have a workflow for binning the data before onward processing. 👍

Image0335W.thumb.jpg.5ef32827b3a90ddf49623953cdaf6d20.jpg

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The clear sky over my part of Shropshire has not materialised tonight  so I have had another go at this data. Reading Ivo's notes on the binning tool in StarTools I really should be binning the OSC data at 25% so I had a go and this is the result. Still not getting the golden hue usually seen in images of IC342, but it hasn't got the palette usually displayed for M51 or M101 either.

Image10AP.thumb.jpg.045a3f52369aafd373b0374272ed345c.jpg

 

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  • 2 weeks later...

With in situ calculated color-colot plots in APP, you have control over the color calibration. Useful when no connection available to do photometric cc using a database, but leaves the result to users choice of stars and that needs to be carefully done, especially in full moon BB data where blues are not the same as new moon imaging.

With a good fit to the color-color plots in star color calibration ( correct balance in blackbody modelling of main sequence stars that are mostly yellow to red) and fitting of the slope trend lines, the amount of golden hue you normally see here, m101, fireworks galaxy, and others, can be altered with choice of the magenta-green sliders in APP color calibration. 

To check if full moon imaging affected color, you could run photometric cc from databases using PI or siril to see if the data is has some color issue, or if it is just the APP fitting/settings.

You can also downsample bin in APP during integration. Mitchel-Netravali rather than Lanczos-3 is good for this.

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On 12/01/2022 at 20:13, vlaiv said:

Second objection is very strange effect around stars. It looks like there is "smooth" halo around all bright stars that is rather distracting:

image.png.54c5b6280efa47ba075b93d2aa6becb8.png

 

@tomato star reduction through morphological transformation replaces the affected pixels by a calculated value; the same calculated value for all the pixels in the "sample" or morphological cell size. This creates a smooth halo around reduced stars. I always add noise to these halos so they look more natural. I use PI noise generation tools with the star reduction mask still in place. Test on a preview to determine the best noise level.

Edited by wimvb
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This image has evolved to something very nice! Regarding the smooth areas around removed stars, I had the same effect with PS Star Xterminator AI version 5 but it is gone from the new AI version 7, but that one introduces other artifacts that I found can be treated with a light touch of the Dust & Scratches filter in PS.

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