# Prime Focus – Imaging Planets
https://steemitimages.com/DQmQrHDGV12kxo8rzicWtE3GCy8k6sWJNtU1LLTHBTcApXd/clipX_g3_ap2X-LRGB_sharperBlueAligned.jpg
*This image of Saturn was obtained May 27, 2017, by the author using a C14 telescope and Minicam5f camera from Brisbane, Australia.  Note the multiple division’s in the ring, the extensive cloud banding on the planet, as well as the planet’s polar hexagon*

In the last installment I looked at prime focus imaging, and this time I want to demonstrate an actual start to finish image processing workflow of a planet, in this case Saturn.  I hope readers find this interesting as there is quite an incredible amount of detail that can be teased out of the images.  Some amateur astronomers are now getting images with resolution starting to approach the Hubble telescope, which is just extraordinary!

This is not meant to be detailed “how to” guide but is instead shows the type of workflow involved in maximizing detail in planet images.  For more detail I’ve linked further details below.


## Starting Data

Below are 10 frames from an actual video sequence of Saturn made last year in July using my C14 telescope with a color camera.  All up there were 12000 frames acquired over about a 5-minute period.  During this time the seeing, a term astronomers used to describe how steady the air is, was relatively poor and you can see this by how the planet shimmers in the video.  This is typical of the conditions most people would experience viewing Saturn.

<center>![22_04_12-x_pipp.gif](https://steemitimages.com/DQmPbtNppJrps5drSPD5fkgvYXB4bYgpEk21gtG4SFHFSvs/22_04_12-x_pipp.gif)</center>
<center>Sample data from 5 minutes of video of Saturn through Telescope</center>

As an interesting point, Saturn’s rotation period is just 10 hours, meaning that even in a period as short as 5 minutes it has rotated 3 degrees, which is enough to start blurring detail on high resolution images.  If you are processing images beyond 5 minutes, it becomes necessary to use a program like [Winjupos](http://jupos.privat.t-online.de/index.htm) to de-rotate the images.  But that’s a subject for another time.

## Preprocessing images
Often data that has been obtained needs to be prepared in a way that it suitable for the processing stage.  Typical operations at this point include:

* Convert image/video format to one that works well with subsequent processing (in this case .avi files are ideal)

* Centralise and stabilise an object in video, making it easier for later processing operations

* Trim the video to reduce the amount of data that must be processed in later stages

* Join multiple video or image files into a single AVI video file

A good program for the above operations is [PIPP (Planetary Imaging PreProcessor)](https://sites.google.com/site/astropipp/) which can be downloaded for free.

## Aligning and Stacking
An excellent program for aligning and stacking images is [AutoStakkert](http://www.astrokraai.nl/software/latest.php) which also another free program.  In a [previous article](https://steemit.com/steemstem/@terrylovejoy/astronomical-imaging-stacking) I described the benefits of stacking images.   AutoStakkert not only stacks and aligns images, but it can remove some of the distortion caused by atmospheric seeing.  Here is how it can be used to process the Saturn data.

**Step 1** : The Saturn video obtained is dragged onto the AutoStakkert as follows.

![autostakkert-1.jpg](https://steemitimages.com/DQmWuskCJatF92bSC5gYAx2m9pvS875kirtoKqDy9yawKdw/autostakkert-1.jpg)

**Step 2** : The analyze button is clicked.  The settings for Image Stabilization and Quality Estimator have been selected for this type of image. 

![autostakkert-2.jpg](https://steemitimages.com/DQmTpvkV3wuFAJsFcrSwPAQUE1FH6aBSWKjwLtyUciEDYBk/autostakkert-2.jpg)

**Step 3** : Once the Analyze process is finished another screen pops up with all the video frames sorted in best to worst quality.  Alignment or anchor points are selected on the planet that represent well defined detail, these will be used to track distortion between the frames and compensate accordingly.  

![autostakkert-3.jpg](https://steemitimages.com/DQmddnACi8auCjPig9jvJK26WhHY8Mz9QMXcSGA5SnzusvN/autostakkert-3.jpg)

**Step 4** : Now that alignment points have been set, the stack process is initiated.  It is typical to stack the best 50% of the images, and reject the others but here I am selecting to do 4 different stacks of the 1000, 2000, 4000 and 6000 best images to see which gives the best result.  

![autostakkert-4.jpg](https://steemitimages.com/DQmRS2mheuTbBbjS2LsVygJ1EReAvXBqNhrTBPufn4jfXq6/autostakkert-4.jpg)

After the above process was run, 4 different image stacks were generated as below.  It seems there is not much difference between the 4 different images, but you will see the difference the better signal to noise in the larger image stacks has when we apply sharpening next.

![saturn-presharpen.jpg](https://steemitimages.com/DQmep5G7okzTe5f9DrpSFwq9dEYKP6jeKnhbP82RqU4mdDn/saturn-presharpen.jpg)

## Application of Wavelet Sharpening

A complete explanation of Wavelet Sharpening is beyond the scope of this article, but it is a sharpening algorithm that applies across a range of small to large detail.  It works very well for maximising detail in planets.  One of the best programs out there for wavelet sharpening is [Registax](https://www.astronomie.be/registax/) which is yet another free program.  Here is the process.

** Step 1 ** : The stacked Saturn image is dragged into Registax as follows.

![registax-1.jpg](https://steemitimages.com/DQmQyYj2SKCSoxwsbehrFTNDjR7HKXDsNwpj2YGp1Znfb35/registax-1.jpg)

** Step 2 ** : When the image is loaded, there is a number of wavelet schemes here that can be applied. 
 
![registax-2.jpg](https://steemitimages.com/DQmagSUkUrstpCwTEwup9vqXEZq3KJCnvoiaUXzaxePbHxA/registax-2.jpg)

** Step 3 ** : If we choose a wavelet scheme based on a gaussian profile, we will see a preview below.  There is a balance to how aggressive to apply the filter, too aggressive will introduce ringing artifacts.  Generally, it is best to apply the filter gently.  Here is the result, as you can see it’s quite dramatic!

![registax-3.jpg](https://steemitimages.com/DQmbvpXy9CivRdqXAqkNxTFEa5jQJ8XdgXm4KZtH14ejN5E/registax-3.jpg)

Finally, this is the output from Registax of the 4 different image stacks.  The 1000, 2000 image stack is relatively noisy.  There is possibly a slight loss of resolution with the 6000 image stack (because a significant number of poor images are included in that stack) but overall it is probably the most presentable.

![saturn-postsharpen.jpg](https://steemitimages.com/DQmW4AJRYMHBpiDHMj1uGgeqgQ6EommFMZ6nLFGaqPf8vKp/saturn-postsharpen.jpg)

## Conclusions

In conclusion we have seen we can greatly enhance the resolution of the planet Saturn through stacking multiple frames from the original video.  We have managed to process a video of Saturn that look like this:

<center>![22_04_12-x_pipp.gif](https://steemitimages.com/DQmPbtNppJrps5drSPD5fkgvYXB4bYgpEk21gtG4SFHFSvs/22_04_12-x_pipp.gif)</center>

To generate this still image:

<center>![final2.jpg](https://steemitimages.com/DQmPEYU4o55HyfCjQ4s4nT6btM9jc5S6Gdh45gvoe7XkRq3/final2.jpg)</center>

I think you will agree the final result is very good given the original images we had to work with!

## Further Reading
Some useful information of wavelet sharpening, and general image processing can be found here (warning this is heavy going!):
1.	E. H. Adelson, C. H. Anderson, J. R. Bergen, P. J. Burt, J. M. Ogden. Pyramid methods in image processing (1984)

2.	Bovik, A. (2009). The essential guide to image processing. Burlington (Massachusetts): Academic Press.

Here is some practical instructions on planetary processing:

1.    Emil Kraaikamp - author of AutoStakkert discusses in more detail the stacking process in AutoStakkert itself [here](http://www.ajax.ehu.es/Juno_amateur_workshop/talks/04_02_AutoStakkert_JUNO_Emil%20Kraaikamp.pdf)

2.	Chris Go is one of the worlds foremost planetary imagers  presents [here](https://www.youtube.com/watch?v=8MeZhlV7p_Y)

**NOTE:**  All images are the author’s, please feel free to use them but I ask you credit them @terrylovejoy