What is true color in Space? We know violets are blue and roses are red, but what does M1 or M101 really look like? Here on Earth there are so many variables due to the thick atmosphere that undoubtedly alter the color by the time it gets to the camera. I think this is the most difficult aspect of imaging, especially with many hours of data. Now the “Hubble Palette” really confuses everything. I never could get into narrow band imaging for the reason that I just can NOT get used to the color green in Space.
Several methods exist to try to get as close as we can to the “true” color. That’s not the main subject today though. After finishing close to 40 hours of imaging for M1 I went through the processing and came up with these 2 drastically different results! Interestingly the color calibration is exactly the same for both. The difference was in the first run I was trying in my mind to create a result that I THOUGHT was the most accurate. Certainly the resolution and detail is fine, but there is very little color except the Ha on the fringes of the nebula. That is because I basically processed it out. I THOUGHT it should look a certain way. When we create these images most of us look at previous ones. Maybe there was an APOD of your image so you want it to look like that. I think this is a path that leads to nowhere. For M1 I was not able to find more than 1 deep image that was not narrow band so I didn’t have much to go on. I thought to myself “we really need to push the Ha detail because that’s what everyone else did”. In doing that I created an image that was washed out, overprocessed and unnatural. I went back and redid everything. I made sure my background gradients were eliminated before combining the RGB with Luminance. I did little if any stretching of the image and I just let the data speak for itself. If you think about it, I had close to 30 hours of binned color, plus the Ha! It had to go somewhere! And of course somewhere it did go, which was the second image. At first I did not believe the color, but I checked several calibration methods and they all came out the same. I asked a couple of the local astronomers here and they said that this was in fact consistent. The deep blue is expected from the high energy synchrotron radiation caused by rapidly moving electrons in an intense magnetic field created by the neutron star we know is at the core! So there you have it. I discovered something above and beyond taking a picture! Trust your processing methods if carefully done and the colors they produce even if you haven’t seen them ever before! Discoveries are still out there for astroimagers!
This was the first run of M1. Nice detail is seen but the core is pale and washed out. The edges of the nebula are overstretched and unnatural looking.
Quite a difference here with rich color both in the core and even the outer portion of the nebula where there are some heavier elements in addition to hydrogen producing some hints of green (did I say “green”?)