I believe the main purpose of photography is to share a view that otherwise couldn’t be seen. That can take a lot of different forms. It might be to record a scene to look at later or to share with a friend or loved on. It might be to use technology to reveal something unseen. Or it could be to represent your personal artistic view to share with others.
The six images above of the Pac-Man Nebula certainly fit those categories. The first image is a simple, color image of just the stars. It’s what you might see when looking through a modest telescope. With a bigger telescope or a simple color camera you might get a photo like the second image that starts to reveal the faint structure of the nebula which is composed (in part) of a combination of hydrogen, oxygen and sulfur gases along with clouds of dust that obscure stars in the background.
The third image starts to explore alternative technologies to pull out even more detail. In this example I used a monochrome (B&W) camera with special glass filters so that I could capture a set of images where each one showed the structure of one of those gases. One very common and simple approach is to color-map the hydrogen image as red and the oxygen image as blue-green to create what’s known as an HOO color palette. It’s a popular choice since it mimics natural color, but it doesn’t show the structure all that well. It also completely ignores the contribution of sulfur.
The next three images all show some combination of hydrogen, oxygen and sulfur in three different color combinations. HSO is an extension of the HOO color palette which adds sulfur as yellow-orange. The SHO color palette (also known as the Hubble palette) switches things up by mapping sulfur to red, hydrogen to green and oxygen to blue. Sulfur and hydrogen as both red but sulfur is slightly “more red” so the SHO color palette keeps the colors in their natural order from most to least red.
The last version reverses the order by mapping oxygen to red and sulfur to blue. It’s by far the least natural color combination, but it may show the most detail by using color contrast to highlight the presence of the different elements.
Which one is “right?” Well, it depends on you and what you want to show. You’re the artist, so you get to choose for yourself. Any answer is fine as long as you’re honest about what you did.
Want to play along at home? The four images above are the basic hydrogen. oxygen and sulfur data (with stars removed) and the RGB stars alone. Click on each image and save it to your computer. Then open them in Photoshop and play with color mapping.