Detail study of the M81 core (black/white negative)

[Menno555]

I always like doing something extra with good captures. This time no animation with moving stars but a detail study of the core of M81 Bode's Galaxy. All the details of the capture can be found in my other M81 posting here

I knew I wanted to do it in black/white and negative because way "more" is visible then. But doing that the normal way (TIF image with RGB color channel) didn't gave as much detail as I wanted. Neither did working on each color channel.
And maybe this is normal for the mono camera people, but I devised a way that worked: I loaded the stacked FITS into Siril, did a Photometric Color Calibration and Histogram action and then I did split the channels, resulting in 3 grayscale TIF files.
In Photoshop I did not use those as color channels but I layered the 3 TIF files. Now I could work on each layer (which essentially were channels) with all the tools/filters/actions, something that could not be done with channels only.

And then a rollercoaster: I tried many, many different combinations with settings, filters, noise reduction and so on, where the Camera RAW Filter helped a lot. Main goal was to get as much as possible detail with as less as possible noise.
This succeed so well, that I really could focus on the core and even could do a magnification. The original capture is 4944 x 3284px with a FOV of 41' 41.59" x 27' 41.65" and 0.506 arcsec/px

The inner core is blown out but there was nothing visible there anyway, so I could even get the very faint dust lanes right next to the inner core
And (like usual) I did not check other captures/images like this to prevent me being biased on it, so when somebody pointed me to https://sci.esa.int/web/hubble/-/41193- ... tral-bulge I really was surprised: the Hubble capture of course is WAY more detailed but the same things are captured.
For comparison I made a black/white and negative version of that Hubble capture.

Personally like the end result a lot. Reminds me a bit of Jupiter's Great Red Spot too because some of the flow patterns.

M81 core negative

M81-Core-Negative.jpg (488.15 KiB) Viewed 886 times

Hubble capture core M81

1567218682931-heic0710d410.jpg (129.21 KiB) Viewed 886 times

[timh]

That is exquisite Menno. Time for Hubble to give up perhaps . You have a lot of sharp high resolution data in there which is testament to you doing something right.

You inspired me to take a quick look at some luminance images that I took of M81 at a nominally similar image scale (at BIN 1 the ASI294MM has 2.8uM pixels) and to try a low stretch and using the PI HDMR tool on the core - and OK but not a candle to the detail you have there.

Your picture also makes a wider interesting point. Most of the time we all (or at least I) obsess about finding faint detail - which creates all of the problems associated with the need for dark skies. But actually there is often just as much to see in the usually blown out brighter regions of objects. I recall a nice image of the M42 Trapezium posted here recently. I have also taken a low stretch approach to a few bright things like that in the past -- mainly planetary nebulae of course and also the core of M87 in order to find the detail and to see the jet associated with the black hole. But I have not thought to use the negative image technique which works very well.

Thanks
TimH

[Menno555]

Thanks Tim!

This whole switch-to-negative is actually just fooling our brains. This image for example looks kinda smooth with details now. If you make this positive again, suddenly you'll see noise, it's all a bit brown, the stars and core are too bright, and so on. Yet it's exactly the same image, with the same details.
Our brains are wired to see and process everything in color and positive. Because of that, we will see flaws like noise way easier when it's a positive image.
But when it's a negative image (especially grayscale or like this, a touch of an even shade of color) the need to detect flaws is gone because we are not used to process it this way. As side effect we think we see more details.
An easy way to experience that yourself is to download a big image of a unknown face with the hair good visible. Now make that image grayscale. There will be almost no change in perception because your brain is used to positive. Now make that image negative ... and I guarantee you that you will see more detail in the hair, it even looks sharper Add the same for for the skin: what looked fine in the positive image, you will suddenly see imperfections (presuming they did not Photoshop it out )

And yes, a lot of times there is way more data in the lighter parts in a capture (as long as it is not clipping). I experienced that the first time last year with M31 and the map I made with all the globular clusters in it. A lot of those clusters only became visible after working on the bright stuff.

Btw, thanks for mentioning M87! That's really something that right up my alley

Menno