M83

[stanlite (Grady)]

So continuing on my galaxy quest with my tiny APO i moved from Cent A to M83 this comprises a total integration of approx 10 hours.The image is heavily cropped to about 1/4 original size due to issues with flats for the Lum channel causing artifacts.

Details:
APO TS102mm
EQ6
ASI1600mm
429x60s = Lum Astrodons
45X120s = RGB Astrodons

I am still struggling with colour balance due to being red green colour blind lol

Comment and criticisms welcome.

Regards Grady

http://astrob.in/297295/0/

[Placidus (Mike and Trish)]

Hi, Grady,

I can help a bit with the colour-blindness. I'm a one-in-a-thousand no-red-receptors-at-all astrophotographer. Here's what I do:

(1) Adjust the black point to be the same in all three channels. You have a strong blue cast in the background. The way I do it is by looking at what I call the 'foothill' of the histogram - the place where the histogram first kicks up from zero counts. Make that place equal and just comfortably above zero in all channels. Another way is to make the peaks on the histogram match on all three channels. Yet another is to find a bit of background, measure the average count in all three channels, and make it the same. Fixing the black point must be done first, and must be done accurately.

(2) Put a box around a feature that you want to be colour neutral. This could be the whole image (especially for narrowband), or just your galaxy. Measure the average signal in each channel. Tweak the linear gain on each channel until the average is the same in each channel. Your feature is now not its "correct" colour, but "colour agnostic".

(3) Increase the saturation to exaggerate the differences between features. In the case of M83, the core will go pastel orange and the spiral arms will have blue dots on a magenta-red background. We colourblind folk will see the orange core and the blue dots but not the red. If you have not made the galaxy "colour agnostic", but your galaxy is say green (or blue, or red) before you increase saturation, you won't bring out differences, you'll just make it screamingly green (or blue or red).

(4) You'd think that in the case of a starburst galaxy, the galaxy really is on average blue, and you'd want to make it definitely blue as a last step, and in the case of a giant elliptical, you might want to make it not colour neutral but definitely orange as a last step. I've never found this to be necessary.

(5) Now see what non-colourblind people are seeing: Prepare a version of the image where you swap the red and green channels. Your green receptors now see what they were seeing in the red channel. Blink back and forward between the two versions a few times. It is very revealing.

The steps must be done in the order I've described, or chaos ensues.

The technique works even better for narrowband images using Hubble palette.

Best,
Mike

[stanlite (Grady)]

Sorry to res this thread but after having spent a bit of time reading up and learning pixinsight again i have a new submission for this galaxy. Same data different processing technique.

Once again i welcome your criticisms

[RickS (Rick)]

Very robust colouring, Grady, but I like it