Is it worth it to stack and process multiples vs. a single exposure?
I think so.
It’s more work, it takes more effort, but in the end the image quality you get from stacking multiple exposures can drastically improve your final product in multiple ways.
Reduce noise with reality
Stacking multiple exposures reduces noise by increasing the signal:noise ratio using reality. I like that.
But, what is signal and what is noise? It’s pretty simple — signal is the stuff (light) we want, noise is the stuff (camera sensor errata) we don’t want. One of the best benefits about stacking multiple exposures is the dramatic increase in the image quality, noise removal, by increasing your signal:noise ratio.
When you stack, you reduce the differences in the digital representation of the light that hits and excites the camera sensor. Each time you shoot an image, the electrical characteristics of the sensor cause it to do its best at representing the photons it “sees.” However, from shot to shot, there are slight brightness and color variations on each pixel for the exact same image. Image stacking produces an intelligent average of each pixel of all exposures, detail for detail, instead of trusting just one exposure and hoping it’s accurate. Sounds like a good idea to me.
This is a 200% zoom of a single 180-second Milky Way image, note how many stars are lost compared to the stack (right).
This is a 200% zoom of five stacked 180-second Milky Way images (which include the single image on the left and four others.)
Along with decreasing noise — you are also able to saturate your images to get more accurate color because you are boosting signal instead of boosting the noise.
Single cropped raw image of Omega Centauri. Look at the noise!
18 stacked raw images of Omega Centauri, integrated in PixInsight. Less noise, more stars.
I’ll let you compare for yourself. Below you can see an example of a single 180-second (tracked) Milky Way image, followed by a stack of 5 different exposures (180-seconds each). Both were post-processed a little differently from the same raw images, but after stacking, there was lot more data to work with.
How you do it
There are a few good software packages out there. Some are free, some are not.
I’d highly recommend PixInsight, it’s what I’d consider the gold standard — but isn’t free and it has a big learning curve. It’s worth it, though!
So, if you’re just starting out — give Deep Sky Stacker a try. It’s free and easy to use, and works pretty darn well, too. Once you have a TIFF image from your stacking in DSS, you can edit it with your favorite image processing application and tweak to your heart’s content. And the best part is, you know that what you’re working with is more accurate data than a single exposure.
Try it out!
Have I piqued your curiosity? I’ve got some homework for you, then!
Go download some of our data to play with and stack (or not stack) yourself, and share the results with me!