CCD Imaging Primer
	Imaging Made Easy and Fun!

Note: Maximum Entropy Deconvolution is an advanced feature of MaxIm, so I would advise people not to bother with it until they have become familiar with the techniques of processing discussed earlier in this primer.

1. What Does It Do?
2. Preparing Your Images
3. Finding Your Camera's Gain
4. Preparing MaxEnt
5. Running MaxEnt

1. What Does It Do?

Maximum Entropy (MaxEnt) is a way to remove blurring from your images. Stars will then be much smaller and nonstellar objects will show more detail. An example is shown below.

NGC 1365 before deconvolution...

...NGC 1365 after deconvolution

You should note that MaxEnt only works on monochrome images. As well, this is only a very basic discussion of MaxEnt, just enough to get you started. You should consult the MaxIm help file for a much more detailed discussion of MaxEnt.

2. Preparing Your Images

Before running MaxEnt, you should do the following to your images:

1. Calibrate (apply your flat/dark/bias frames, if any)
2. Combine (if you are doing a series of short exposures to get a long exposure)
3. Square pixels (MX cameras have rectangular pixels)
4. Remove hot/dead pixels (use the "Kernel Filters" option on the "Process" menu)

Save all other processing for after you run MaxEnt.

3. Finding Your Camera's Gain

Before you can run MaxEnt on images from your camera, you need to determine the gain (ADU number) of your camera. The "Photons Wizard" is used for this task. There are four ways to get your ADU number:

1. Enter the number from your camera's manual (note: the Starlight camera manuals don't contain this information, so that takes care of this possibility!)
    
2. Enter Full Well Capacity and Bit Depth values for your camera.
    

   Camera Model	Full Well Capacity (electrons)	Bit Depth (bits)
   HX516	40,000	16 bit
   MX5	120,000	12 bit
   MX516	120,000	16 bit
   MX5C	120,000	12 bit
   MX916	300,000	16 bit

   
   
3. Choose your camera from the list in the Photons Wizard (e.g. Starlight MX5 or HX5)
    
4. Have MaxIm calculate it from some of your flat frames. MaxIm requires that you have at least five flat frames and five bias frames. All you have to do is choose them and the Wizard does the rest. You will be shown the calculated ADU number in the final Wizard screen.

The last way is probably the best, since there may be significant variation in gain from camera to camera (depending on how closely this is controlled by the manufacturer).

4. Preparing MaxEnt

If you are using the "MaxEnt Wizard", there are five steps:

1. Image Type (choose "Long exposure astronomical image")
2. Star Selection (choose "Automatic")
3. Camera Type (choose "Cooled CCD")
4. Noise Model (choose "Automatic")
5. Run MaxEnt

If you are not using the MaxEnt Wizard, do the following:

A. From the MaxEnt menu, select the "Set Point-Spread Function" item.

1. click "From Image" under "Function Type"
2. click the "Select From Image" button (the dialog below appears)
    
   
   
3. click on a star in the image (fields in the dialog are filled in automatically, as below)
    
   
   
4. click "OK" in the "Select Point-Spread Function" dialog
5. click "OK" in the "Set Point-Spread Function" dialog

B. From the MaxEnt, select the "Set Noise" item.

1. Click "Poisson"
2. Click the "Auto-Extract" button
3. Click the "OK" button

C. From the MaxEnt menu, select "Run MaxEnt" item.

5. Running MaxEnt

If you chose to run MaxEnt via the Wizard, then at this point two windows will appear, one on top of the other. The top window contains instructions on what to do. Drag this window to the side so you can see the "Run MaxEnt" window underneath, then follow the instructions. If you did not use the MaxEnt wizard, the dialog shown above appears by itself.

Now select the "Preview" option, choose the number of iterations to run, and click the "Go" button. You will see the thumbnail preview change with each iteration completed. Watch closely.

A star image from start to finish in MaxEnt. Stars should be smaller when you are done, but unfortunately examining the star images alone won't tell you when to stop running MaxEnt.

The image should appear to get worse, then better. The trick is to do just the right number of iterations: even just one too many won't result in a nice image. Use of the "Undo Last" and "Undo All" buttons in the preview mode can help greatly in finding the right number of iterations. Another technique is to do a few iterations to start, and then do one at a time until you get where you want to be.

Once you have determined the best number of iterations, click the "Actual" button, then the "Go" button. When MaxEnt is finished running, you may notice dark areas around bright stars in the image. This happens quite often, and most people simply "paint" them out in their favourite bitmap editor!