FWHM Preferences Page
The FWHM Preferences page configures Radial Profile Plots and the FWHM Measurements tool used for computing the point spread function of the image.
To open the FWHM Preferences page, open the Mira Preferences dialog and select the FWHM tab.
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Max Radius |
Specify the maximum radius to use in the FWHM calculation. This is the radius of the background beyond the point source, not the radius of the point source. |
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Auto Centroid |
Check this option to automatically compute the centroid position for the point source. It is recommended that you check this box. |
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Fit Gaussian + Constant |
Check this box to compute a fit to the profile of the point source. If the calculation is made, Mira reports the point spread function parameters of FWHM, Peak Brightness, and Background value. |
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Advanced |
Opens the Profile Fit Properties dialog (see below) for use in the Gaussian + Constant fit. |
The Advanced button opens the Radial Fit Properties dialog where you set parameters for radial profile fitting used in the FWHM calculation. Profile fitting is an iterative procedure which requires starting values. The FWHM starting value should be reasonably close to the final value, say within 50% or thereabouts.
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Use S/N Weighting |
Check this box to weigtht the solution by the Signal to Noise Ratio of the pixel values. Checking the box usually gives a better fit to the point source and unchecking the box usually gives a better fit to the background. |
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Max Iterations |
Set the maximum number of iterations for computing the fit. A value of around 300 to 400 usually works well. |
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Initial FWHM |
Set the initial value for starting the profile fitting. His should usually be within 50 to 100% of the actual FWHM, as measured in [pixel] units. |