Single Shot Color Imaging

“Life is like art. You have to work hard to keep it simple and still have meaning.”

- Charles De Lint.

Simplicity lends itself to increased complexity, and though the end one can appreciate returning to the beginning, where we again see elegancy in the reduction of such complexities. (OK, I made that one up). Such as it is with single shot color imaging. Who knew?

Color CCD cameras are straightforward to use, and so are a good tool for beginning imaging. Instead of taking multiple images in B+W and using multiple single band color filters to put together and then try to color correct, one can merely click a single image to obtain a reasonable representation of a brighter sky object, or even add and average multiple images together in order to decrease noise and bring out detail in more dim objects.  The camera does most of the color work through a Bayer interpolation of what the human eye is accustomed to seeing. Several GRAS cameras allow one-shot imaging of various objects, and as the year progresses, many different targets are available to photograph.

It is very rewarding to see some results right away, without needing to work hard on processing your data. The calibration of the color images is even done for you! But what if you have taken some different single images and now want to work a little harder to improve your data?

If you like adding complexity to life, then obtain more images of the same object, and average those together. Why would taking more images of one object make a better picture? It’s an issue of data and signal. The more data you can collect, the stronger the signal in more dim areas, and the more the eye can pick out when that detail is enhanced (or, in other words, noise is reduced). The same basic ideas apply to all CCD cameras, but with single shot color, you just need to process one series of images instead of four ( luminance, red green and blue) or even six ( if you like to use RGB and narrowband, but that’s another story).

Bubble Nebula and friends. G-20 . Ten 600 second images.

By adding images together, the noise is reduced significantly even by comparing 4 averaged images to one image, but there is a practical limit- without going into the math, six or ten single images added together will give some reasonable results. There are also methods of removing unwanted data such as cosmic ray hits (bright lines) and camera artifacts, and several software utilities such as CCD Stack, and Maxim DL as well as others that are freeware allow you to do just that.

Now, if you want to work still harder, you can take your multiple calibrated images, align them and remove unwanted data and then average or otherwise add them together, and then bring the final image into Photoshop where you can duplicate your color image, desaturate one of the image layers, and then process a color layer and a luminance layer separately. This allows more control of color bias, saturation and balance, ( you can even apply a little Gaussian blur to your color layer as well) and also allows the luminance layer ( where the eye gets most of its “detail data” anyway) to be manipulated separately to enhance dim details, reduce noise in dim areas and sharpen detail in bright areas; much more complexity but better control.

Garradd. G-20. Total of five 300 second images.This would be a good exercise for someone wanting to learn some solid processing techniques without needing to fuss with multiple color bands. There is always something more complicated just waiting for you to find it. Yes there are drawbacks of single shot imaging, of course. Because there is a series of tiny small color filters in front of the detector, and for other reasons, these detectors just can’t be as sensitive as B+W cameras using single color filters, and so it takes more time to image, and some objects therefore are just are not amenable to single shot color.

Having said that, I and others even use digital cameras to shoot the night sky, so I don’t want to belittle the Canon fans out there. So if you have any interest in imaging but don’t know where to start, try some single shot objects, and go from there.

the sky awaits.

Carl Tubbs.

See Also Dr Christian Sasse’s video on Color Processing - Below