Announcements After a short lecture we will adjourn to the Farm. Tonight is a Dark Sky make-up night. Class will meet Thursday night. If clear: meet at the Farm. If cloudy: meet here. Next week: 1st Quarter Observing Night Wednesday night. Set-up will start around 6:30pm. Class will meet Tuesday as usual. Thursday class won’t meet next week.

CCD (and DSLR) Image processing

Problem 1: solid-state devices suffer from thermal noise Atomic vibrations (heat) produce electrons just like photons do. An electron is an electron however it is produced so the heat produced electrons create a constant “noise”

Solution 1: cool the chip Digital cameras do not have cooling so they have problems with long exposure times.

Solution 2: take dark frames, lots of them, and average them Take a picture with the shutter closed. The only thing that is imaged is the thermal noise. The image must be at the same temperature and have the same exposure time as your actual image.

Problem 2: pre-bias and readout noise A pre-bias charge is required to “activate” the chip. The readout process can introduce an electronic noise during transfer

Solution: Bias images The bias image is a zero time exposure with the shutter closed. Zero time eliminates thermal noise so the only thing “imaged” is the bias and read-out noise.

Problem 3: irregularities in sensitivity across the chip and dust in front of the chip

Solution: Flat Frames Take images of a uniform white background

Image Calibration using MaxIm: Bias Be sure the temperature is the same as your data image was taken at Set the exposure time to zero or as short as possible Take ~10 images then average them. Save the result as master bias Usually you will want to identify it with a date so: Masterbias091917

Image Calibration: Darks Make sure camera is at same temperature as the data image was taken at Set exposure time to the same as the data image used Take ~10 images with the shutter closed then average them Save the result as Master Dark Identify with a date: Masterdark091917

Image Calibration: Master Flat 1 A set of flats should be taken whenever the camera is taken off the telescope or rotated since dust specks will move. As with all calibration images, make sure the camera is at the same temperature as the data image was taken at Find a plane white background to image Large whiteboard evenly illuminated, Flatbox or twilight sky

Image Calibration: Master Flat 2 Set exposure time to reach 35% - 50% saturation. Saturation is found by dividing the full well capacity by the camera gain. Both numbers are found in the camera manual. Once exposure time is determined, take ~10 dark frames of the same time and create a Master Flat-Dark. Take ~10 Flat frames. If possible, spread them out over the imaging session: a few before your first data image, a few halfway through and a few more after completing your data images.

Image Calibration: Master Flat 3 Subtract the Master Flat-Dark from each flat frame. Save each as Flat-DarkedXX Again, adding a date identifier helps Flat-Darked01-091917, Flat-Darked02-091917 up to Flat-Darked10-091917 Average all the Flat-Darked images Save the result as Master Flat. Again, add date identifier: MasterFlat091919 If you are doing CCD color imaging, each color must have its own independent flat frames

Image Calibration: Applying the Masters to the data images Subtract the Master Dark from each data image Subtract the Master Bias from each dark subtracted image…not needed if doing dark frames each evening. Divide each image (after dark and bias*** subtracting) by the Master Flat You now have calibrated your images. Save them as imageID-Cal