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Notes on Using a Webcam for Planetary and Lunar Imaging and Registax for Processing the Images
By Alan Jefferis

In my view the method of using of a webcam for capturing still images of planets and the Moon is hard to beat from the points of view of both quality and cost. The method can be summarised as capturing a short video sequence in the webcam and then using software to separate out the individual frames, align them, pick out the ones having the best quality (perhaps only 10% or so of the total) and then combining the best frames into a single image. I use the Phillips Toucam Pro 2 but this has now been superceeded (by the Phillips SPC900 I think). You will also need an adaptor to connect the webcam, with its lens removed, to the telescope. These are available from several of the main astronomical equipment suppliers. The software I use is Registax, available as a free download. Just Google for registax.

Capturing the image sequences

Attach the webcam (with its lens removed) to the telescope and, for planetary imaging, use as long a focal length as is practicable – eg use a 2x or 3x Barlowe. The main planets can then fill a reasonable portion of the frame. With my telescope of 2500mm focal length and a 2x Barlowe Saturn fills about 100 pixels of the Toucam's 320 pixel frame. If your 'scope has much shorter focal length than this you may find you need eyepiece projection to get a decent image size. Moon shots will not need a Barlowe, unless you are trying to capture a very small part of the surface. Get the planet image roughly central and focussed. A large aperture 'scope may have to be stopped down for a very bright planet with a cardboard aperture reducer. I have found that planet images are often significantly more stable later in the evening compared with the period closer to sunset. I use the Phillips VLounge software supplied with the webcam for capture. If you have a different webcam you'll probably have equivalent software. First open the Properties window, either from the Vproperty button on the opening screen or from the Options menu in the VRecord window. In Properties uncheck the Full Auto Control (top right). Set brightness and contrast sliders to the centre of their range. Set frame rate to 15, 20 or 25. Now click the Camera Controls tab and uncheck auto if it is checked. Set the exposure to a value that gives an image with the highlights not burnt out, i.e. not over exposed. You can always enhance shadow detail of a final image using brightness and contrast controls but nothing will recover saturated highlight detail. Close the Properties window. In the VRecord window use the File menu to set the capture file. One thing I find annoying is that if you make a second capture sequence without setting a new capture filename it will overwrite your previous capture. I have written a very small program which enables you to just click a box to rename a captured file by adding the time to its filename, thus avoiding overwriting. I'll send a copy to anyone who asks. Or, if you find a way to avoid this overwriting please let me know it. Under the capture tab you can also set the capture time limit and I usually set this for 10 or 12-second sequences (around 200 frames). Keep an eye open for dust spots on the image. These are normally circular, fuzzy, dark blobs. Brush them off the cover glass with a soft brush. A single one can sometimes be dodged by adjusting the image position slightly.

Processing with Registax

I find that both Registax and K3CCDtools are good at everything except selecting the frames with the highest image quality. Accordingly that is where my method departs from that of just leaving everything to the software. This version of these notes has been updated to correspond with Registax V.4.

Load an avi file recorded by the webcam by clicking Select Input.

You might first like to see what the fully automated Registax process can do, as follows.

- Check the box Automatic processing.
- Move cursor over the image.
- If the box that appears is not big enough to include most of the planet change Alignment box size.
- With the box in position click to lock it.
- Now click Align and let things happen.
- It will stop on wavelet processing. I leave the default parameters.
- Click Final.
- Click Save Image.

Now do it with user selecting the best frames

- Uncheck Automatic processing
- Click Show Frame List (sometimes needs doing twice before list appears). –
- Click Show None at the head of the frame list.
- Click on Frame 1, which will be the one shown in the preview window.
- The next step is to select only the best frames, which may be as few as 10 - 20% or so of the total. This can be done quite fast by having one finger on the cursor-down key and another on the space bar, which adds or removes a check mark by a frame.
- In the frame list move onto any one of your checked files so that it is highlighted.
- Move the cursor to the preview window so the square includes the features most likely to be good for the registration process.
- Click Align.
- Click Limit
- Click Optimise and Stack
- The process ends on Wavelet Processing which doesn't seem to do much to my own images, but at least does no harm.
- Click Final.
- After this there should be a Contrast control and a Brightness control. Use the Brightness to reduce the image to the point where there are no washed out highlights. You're not looking for the best image at this stage but simply making sure there's enough information in it to get the best out of it with Photoshop or Paint Shop Pro.
- Save the image.

Subsequent Processing

What I describe will be based on Photoshop but most can also be done in PSPro, and probably other image processing software. The most important function to have available is Unsharp Mask. In Photoshop it is under Filters/Sharpen. In PSPro it is in Effects/Sharpen.
There are three parameters. Clip or threshold sets the number of levels at the bottom of the brightness range below which the unsharp mask doesn't act, thus reducing the enhancement of noise. It is normally set at 0 to 2. Radius sets the size up to which features (edges etc) are sharpened or enhanced. Increase it to the point at which edges are not over-enhanced – typically up to 5 pixels. Finally, strength or percent is self explanatory – set it to give best result. Go too high and your image will look over-processed.
After unsharp mask there may be benefit in reducing noise that has been enhanced. Do this using Filter/Blur/Gaussian Blur at between 0.5 and 1.0 pixel radius.
Finally, use brightness and contrast and colour saturation if further improvement results.
If you did the run where the selection was left to Registax you might want to process that image similarly to see who did best!

Alan Jefferis

Revised June 2007

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