ajamesmccarthy
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Unedited image and Simulated True Color of My last post, plus an explanation of colors
🕑 Added 2020-08-29 21:05:56 +0000 UTCI get a lot of questions when I post False color images, basically "What does it look like to my eyes" and "Do you just paint colors in?"
Basically, astrophotgraphy is so different from regular photography, that the same conventions do not apply whatsoever. I'm essentially taking pictures of a shadow. Here is a crash course in how color with astrophotography works.
Let's start with your eyes. What would they see?
For me, they see nothing. I point my telescope and binoculars to this area constantly, and even with dark skies, I can't see these clouds visually. Just stars. Is that because They're in non-visible wavelengths? Not really. Our eyes are sensitive to the emission lines of emission nebula. However, they have a very limited aperture, so even enhanced by a telescope, your eyes struggle to see something that is so dark. Some claim to see them in small telescopes, but I never could. Brighter nebula like the Orion or Lagoon nebula are easy to spot visually, but still appear gray. This is because your eyes can't register color in low light. The nebula themselves are quite colorful.
So why is the Raw frame so faint and in black and white?
This is where it gets a little complicated... I actually use a monochrome camera to shoot this stuff, but important to note that all digital cameras are actually monochrome. There is no such thing as a "color sensor" just a sensor that has a filter over it. In the case of most color digital cameras, they have something called a "bayer filter" that covers the sensor, that limits the light from all but specific colors over each sensor pixel to create R,G, and B channels that are automatically blended, colorbalanced, and enhanced to give you a simulation of what you are seeing with your eyes. The problem with these cameras, is they block the vast majority of light that enters the pixels. When shooting something very faint, that is bad.
Since my camera is monochrome, it gives me control over how I filter light. I can put filters over the sensor that only allow light to pass through from specific burning elements, elements that are abundant in these nebulae, but not in my light polluted city. What I showed you is just one of three channels, each looking slightly different, but each are monochrome. When combined, they create color.
The image is faint because I rely on the process of stacking individual frames and "stretching" the image in processing to reveal the details, because If I properly exposed for this image it would cause the stars to be bloated and obscure the image.
So why False color if these things are naturally colorful?
The most abundant elements in these nebulae are Hydrogen-alpha, Oxygen iii, and Sulfur ii. Hydrogen burns red, Oxygen turquoise, and Sulfur red. So I can't map these colors to R-G-B and have it be accurate color like a digital camera can. But, by mapping hydrogen to Green, Sulfur to red, and Oxygen to blue, I can have a detailed image, that is also "false color", The colors now represent information that is scientifically useful, but also aesthetically pleasing. The simulated true color image I showed you actually omits the data from sulfur, and uses a modified palette to simulate what an ordinary digital camera would see if it took a picture of them. I couldn't do this if I tried from my backyard due to light pollution, but if you look back to my image of the Perseid meteor shower you will see the heart and soul nebula and their distinct red color in my image.
I find my version I shared first to be considerably more vibrant, and since really I am doing this for the art, it is the style I prefer. As always though, let me know what you think. Your opinions matter to me and help shape what I am doing, always.
Comments
That was a fascinating read. Thank you!
Always wondered. Thank you very much for that.
