VIDEO IMAGING TECHNIQUES

VIDEO ASTROPHOTOGRAPHY TECHNIQUES
Jim Ferreira
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Video imaging the solar system is an ongoing learning process and much of the progress I have made in my own work is largely a result of input from dozens of other video astrophotographers from all over the world via the VIDEOASTRO E-mail discussion group. With their help and much experimenting I have begun to produce good, occasionally very good, images of the Moon and some of the planets. Below I share some of what I consider important and will continue to add material as I collect it. Should you have questions or suggestions, do not hesitate to contact me at ferreira1@llnl.gov or BakerSt@home.comand I will be happy to share what I can or direct you to someone more knowledgeable.

POINTS TO CONSIDER
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1. Always inspect the CCD chip front window surface for dust particles with a loupe or reversed 25mm Orthoscopic eyepiece before starting a video run. Spotting them later on the monitor, or worse, when your editing images is at best an inconvenience and at worst, a wasted run. Use a clean camel hair brush and air to remove particles (try not to spit). Store the camera with the chip protected by a dust-tight cover.

2. I use the monitor image to judge my video recordings brightness level. Even though the PC23C has auto-gain/shutter you will still have to control image brightness by increasing or decreasing image scale, using filters or adjusting your composition (lunar) to control image brightness. With the Astrovid 2000 gain, shutter speed and gamma are all manually controled. Adjust video monitor brightness and contrast in a darkened room while viewing a well lit daytime scene from your favorite movie video (try not to get hung up on the movie, you have video to shoot!). Certainly there are more precise methods, but this is quick and easy starting point, and appears to be accurate enough to avoid over or under exposure through the telescope.

The need to fine tune monitor settings will be apparent as you start to capture still images to the computer. If the captured images are too dark, your monitor setting should be turned down at bit. If the captured images are too bright then your monitor brightness should be turned up a little. Mark the settings! Next run of images will help you to further refine the monitor setting.

3. 8mm and standard VHS video seem to be pretty comparable in image quality. I recently started to record to a Hi8 camcorder and image quality is much improved over 8mm and VHS. Captured images contain less noise and appear sharper. Hi8 is comparable to SVHS. The next step up is one of the digital video camcorders. Best results from video are direct capture to the computer either by digitizing board or with a fire wire (digital camcmorders).

4. Regardless of VCR format, the capability to review the video in 'still frame' mode is invaluable for finding the sharpest image. Using 'slow motion' if 'still frame' is not available would be the next best alternative. Good images can be captured at normal speed with a little practice and considerable perseverance (though one's vocabulary tends to become a bit more colorful).

5. Orienting the video monitor image borders north-south/east-west by rotating the camera in the telescope focuser makes centering an object considerably easier. I have gone so far as to mark the monitor with N/S/E/W (though I still tend to get confused!).

6. When processing a saved image resist the temptation of over doing it with the unsharp mask and the contrast setting. With video capture, bringing up edge sharpness and contrast also brings up image noise and artifacts in the video recording. Also, pure white highlights are distracting and degrade the aesthetic qualities of the image.


Balance of contrast and sharpness.	Too heavy use of unsharp mask brings up noise.	Too much contrast, no gain in information.

The two Saturn images at right demonstrate too heavy use of un-sharp mask and brightness / contrast processing. With video capture images bringing up edge sharpness and contrast also brings up image noise and artifacts in the video recording. Pure white highlights in a too contrasty image tend to be distracting and degrade the aesthetic qualities of the image.

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STACKING VIDEO CAPTURE IMAGES
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The stacking of images can significantly reduce the grainy appearance of captured video images and improve contrast between dark and light features, thus improving apparent sharpness. Stacking images also eliminates much of the random noise and artifacts. Only those features that appear in each image will remain after stacking a half dozen or more images together.

The accurate stacking of images does not require a highly sophisticated pieces of software such as PhotoShop, Mega-Fix, QMiPs or Maxium. Stacking can be done quickly and effectively with the Adobe Photo-Deluxe (PD)software that comes with the Snappy frame grabber. After familiarizing one self with opening and saving image files, it is only a matter of performing a few straight forward steps to stack an unlimited number of images.

The assumption is made here that images have already been captured to computer memory and can be accessed by the PD program. It is recommended that images be captured at at least 640x480 or higher resolution and be stored in a non-compressing file format such as TIFF.

	1 ) The first step is to go to PD FILE MENU and scroll down to PREFERENCES. There click on the ALLOW MULTIPLE DOCUMENT WINDOWS. You can now open two image files one at a time using the GET PHOTO command. Adjust the window/image size with the +/- buttons so that both can be seen in entirety.
	2 ) Now go to the menu bar and select VIEW and scroll down to SHOW LAYERS. Select one of the two image windows, then go to the menu bar and select EFFECTS and scroll down to NEGATIVE. The image in the selected window will change as seen at left. Next go to the LAYERS window and double click on the thumb-nail image -- change OPACITY to 50%, then OK.
	3 ) Now go up to the menu bar and click SELECT, scroll down to SELECTION TOOLS, then to MOVE (or CTRL 'G'). You now can move the negative image into the window with the positive image by placing the cursor over the negative image, holding down the left button and dragging image over on top of the positive image.
	4 ) Using the ARROW KEYS you can now move the negative image one pixel at a time across the positive image. Overlap the two images and adjust until both images completely merge and cancel each other out. Do not rotate image. Because the images are not identical, there will still be some texture visible -- try to reduce the dark/light texture to the absolute minimum using the ARROW KEYS
	5 ) Once satisfied the images are sufficiently aligned go up to the menu bar and select EFFECTS, scroll down and click on NEGATIVE again. The top image will return to positive, now contributing 50% to the image information, as at left. Go to the LAYERS window and click the right pointing ARROW, then click MERGE LAYERS. The two layers are combined into a single image. Next close the window containing the negative image -- do not save. The original image file will not be effected and remains saved.
	6 ) The next image can now be opened beside the window containing the stacked image and the process can be begun again by making the new image negative and 50% opacity and dragging over onto the stacked image. After each stacking, merge layers. Any number of images can be stacked in this manner. Graininess will continue to be reduced and apparent contrast and sharpness will improve with each new layer.
	7 ) Brightness, contrast and sharpness can now be adjusted using the PD program or saving the image as a TIFF and importing it into any image processing program. PD does have an UNSHARP MASK command -- go to EFFECTS, then SHARPEN, then UNSHARP MASK. Good initial setting would be 50-75% amount of sharpening, 2-6 pixel radius and threshold level near zero. From image to image these settings will vary depending upon what details your are trying to enhance. Be sure to experiment.

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