Points Page (Star Removal)
Most options on the Points page control the way templates and target objects are marked on the images. If you want to set the color of the markers, see the Other Properties page.
The Radius and Tracking Properties affect the measurement of object positions in single images and when tracking positions through an image set. These are described in the table below.
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Mark Centroid |
Check this box to cause Mira to compute a precision centroid coordinate whenever you mark a template or target point. If not checked, then Mira will use the exact position you mark with the mouse. |
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Negative Points |
Choose this option to compute the centroid position based on negative deviations below the background. Use this option when the images being measured are actually negatives (not positives displayed as negative; see Image Palettes and the Palette Properties dialog). |
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Positive Points |
Choose this option to compute the centroid position based on positive deviations above the background. This is the typical case |
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Radius |
Defines the radius, in pixels, from the target point within which pixel data are used to compute the centroid position. A reasonable starting point for choosing a value is 2 times the FWHM. (Note: FWHM measures a diameter and this parameter is a radius). |
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Tracking |
Defines the maximum distance, in pixels, from the current position that Mira will search in the next image to lock onto a new position. This is only used when tracking objects through an image set. |
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Track Centroids |
Controls the duplication of markers when the positions are "tracked" through an image set. If this option is checked, the positions are centroided in every image. |
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Show Template |
Click this button to display the master template in an Image window. If working with an image set, only the template for the current image is shown. |
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Show Samples |
Click this button to display the template samples marked in the current image. The samples are shown as an image set in a new image window. |
Centroid positions are computed using image data, not the screen display. Choose Positivepoints or Negative points based upon the type of object to measure rather than the palette or other image display properties. For modern, inherently digital images, you will almost always choose Positivepoints. However, when working with a scanned photograph you may find that stars are negative deviations from the background, so you would choose to centroid on NegativePoints.