Orion 52083 - Manual (Page 26)

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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. 3.0 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 (Image 14)
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
the amount of blurring applied to the image. Increasing the radius increases
the amount of blur applied.
For best results, turn on the Auto Full Screen preview button, and adjust the
settings. This allows you to rapidly adjust the settings until you are satisfied
with the results. Then, click OK to actually apply the filter settings to the
image.
It is best to use a light touch with this command, to avoid over-processing the
image. Over-processing can create artifacts; i.e. features in the image that are
not real. It also amplifies the noise in the image.
Color Balance
The sensitivity of most CCD cameras as a function of wavelength (color) is dif-
ferent from the response of the human eye. The filters used for creating color
composites also have their own characteristics, as do the telescope optics.
Although “perfect” color rendition is an elusive if not impossible goal (all indi-
viduals see colors slightly differently), it is straightforward to get “good” color
balance with simple weightings. This is where the Color Balance command (in
the Process menu, Figure 15) comes in handy to touch up the resultant colors
in your images. Use the Preview Image to see how altering these parameters
will affect your image (or click the Full Screen button to see the changes
applied to your full image).