Orion 52083 - Manual (Page 25)

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Oxygen-III and Sulfur-II wavelengths are used individually, or in combination
(similar to RGB) to deliver astounding detail and definition of certain types of
nebula, such as emission nebula or planetary nebula. Additionally, narrow-
band imaging remedies light pollution from interfering from the image quality,
thus allowing you to take high contrast images in heavily light polluted areas.
Narrowband imaging is used by the most advanced astronomical telescope
imaging systems, including the Hubble Space Telescope. The same method of
RGB imaging can be applied to narrowband imaging.
Image Processing
After you have captured and combined individual images (with or without dark
frame subtraction) into a single resultant image, you may want to perform
some additional image processing to bring out subtle details or to make the
image appear more pleasing overall. Maxim DL Essentials contains several
functions which serve to do this. These can be found in the Process menu
Make Pixels Square
This command provides a one-step adjustment of the image aspect ratio.
It uses the pixel aspect ratio determined by the file header and interpolates
the image to make the aspect ratio 1:1. This generally has a very mild affect
when applied to images. For best results, this function should be applied to
individual images before stacking (for best image alignment), but can be used
after stacking as well.
To use this function, simply select Make Pixels Square from the Process menu
for any image currently opened in Maxim DL Essentials.
Combine
We previously mentioned in “Imaging Deep Sky Objects” that Average is one
of the methods to combine your images. There are three other methods that
will achieve slightly different results: Sum, Median, and Sigma-Clip. Each of
these methods will improve your image buy stacking it, but each one combines
the images in different ways.
1. Average sums all the pixels and divides by the number of images chosen
to combine.
2. Sum adds up all the pixels in the images. This will increase the Max Pixel
value and the offset in the Screen Stretch window. If you Sum the image,
the file should be saved as a fit in IEEE Float (beyond 16 bits) to preserve
all the data in the image.
3. Median takes the middle pixel value from all of the images. The Median
mode is useful when some pixels are extremely bright or dark (hot/dark
pixels, cosmic ray hits). If Median mode is used, a Normalize option is
available. Normalize will remove differences in the image scaling which
could interfere with the median processing.