Combine Methods; Filter - Orion 52084 Instruction Manual

Set the Screen Stretch Window to Medium (or otherwise manually adjust
for best image appearance), and use Save under the File menu to save your
image. You can now perform any wanted imaging processing.

Combine Methods

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 by 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.
4. Sigma-Clip combines the best features of Average and Median. Sigma-
Clip is the best choice for removing unwanted noise, hot pixels and satel-
lite trails. It works like Average but also calculates the standard deviation
of the averaged pixel values. The Sigma Factor will determine how many
pixels from the standard deviation are discarded. The lower the Sigma
Factor, the more pixels are discarded. 0.5 is a good value to start with.
A new average is calculated without the discarded pixel. This value is
assigned to the corresponding pixel in the output image.

Filter

Filtering an image is an operation that emphasizes certain characteristics of an
image while suppressing others. MaxIm DL Essentials supports two kinds of
filters: Unsharp Mask and Gaussian Blur. In the Filter window select which
one of these filter types you would like to apply.
Unsharp Mask is a method of sharpening or high-pass filtering an image. It
amounts to subtracting a low-pass filtered version of an image from itself. The
low-pass filtered version is called the mask. The Low-Pass Filter itself can
be set to Mild or Strong for different effect. Use Mask Weight to control the
strength of the mask applied to the image. The Mask Weight is in percent; the
higher the number, the stronger the mask.
Gaussian Blur is a method of blurring an image. It can be used to suppress
noise in an image at the expense of sharpness. The Radius setting controls
26