Imaging Technique for the Amateur Astronomer. by Frank Barrett Jan 27, 2007 15th Regional Gathering of Amateur Astronomers. Objectives. Overview of Astro Imaging Requirements Emphasis on Imaging Technique If time permits, A Short Processing Demo End with a slide show. The Question.
by Frank Barrett
Jan 27, 2007
15th Regional Gathering of Amateur Astronomers
What is required to take really good astronomical images?
Technique: a method of accomplishing a desired aim- Merriam-Webster
so when we speak of technique we are speaking of a methodology or perhaps a framework of methodologies working together to accomplish our goal:
Really Good Images!
--> Tools are NOT Technique
Two main phases to image processing:
1) Noise reduction (both random and non random)
2) Signal enhancement
Noise - an unwanted signal or disturbance in an electronic device or instrument; irrelevant or meaningless data or output occurring along with desired information
Signal - a detectable physical quantity or impulse by which messages or information can be transmitted
(ref: Merriam-Webster, http://m-w.com)
Combatting Non Random Noise with Image Calibration (a.k.a. Reduction):
1) Darks - every electronic imaging device produces noise due to “dark current”. An image taken in the “dark” for the time and temperature of your light frames can be subtracted to remove this form of noise.
2) Flats - another form of unwanted noise may come from the optics of our system. Dust, dirt, and uneven illumination can conspire to produce unwanted artifacts in our images. A flat is an evenly illuminated image which can be used as a baseline for removing these artifacts.
Combatting Random Noise by Combining Frames:
Combatting Non Random Noise by Dithering Frames:
A Final Note:
Once we have done a good job of removing noise we can focus our attention on bringing out the signal of our target.
Our primary goal here is to bring out the detail, color, and character of the underlying data. We strive not to distort, but to enhance.
Please Note: It is impossible to remove all the noise and therefore we need to be very careful that we enhance the signal and not the remaining noise.
Most of the signal in a typical deep sky image is in the low end of the histogram:
“What could I have done to make this image even better.”