Source Photometry Parameters
This dialog sets preferences for the Source Photometry measurement performed by the Source Extraction Module. This measurement is selected on the Post Process page of the Source Extraction dialog.
This dialog configures 2 different modes of measurement:
Scale Mode, for Resolved Sources. Use this mode when objects have an inherently different size on the image (i.e., when the objects are not unresolved point sources). This mode uses the detected area at the threshold brightness as a guide to estimating the full size of the object.
Radius Mode, for Unresolved Sources. Use this mode when the sources are point sources all of similar FWHM. In this mode, all sources are measuring using the same aperture size and shape.
The operating mode is selected using either the Scale/Radius tab or the Resolved/Unresolved selection.
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Unresolved sources can appear to have different size because of the way images are displayed. Their extacted areas will also differ because it is measured at a fixed threshold brightness. For unresolved sources, the FWHM is a brightness-invariant measure of the object size. |
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Sources are: |
Selects whether the sources are to be treated as unresolved or resolved. |
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Background Method |
Selects the background method. |
Scale mode uses the effective radius, computed during the Detection phase, to adjust the measuring aperture and background apertures. The effective radius is defined as square root (Area / pi).
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The scale factor which multiplies the effective radius of the object to get the actual measuring aperture. |
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The scale factor that multiples the effective radius to get the inner background measuring aperture. |
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The scale factor that multiples the effective radius to get the outer background measuring aperture. |
In Radius Mode,
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The radius, in pixel units, of the object measuring aperture. |
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The radius, in pixel units, of the inner background measuring aperture. |
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The radius, in pixel units, of the outer background measuring aperture. |
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The ellipticity of the apertures. THis is the value of 1 - b/a, where b is the minor axis and a is the major axis. Circular apertures have an ellipticity of 0; a linear aperture has a value of 1. The maximum allowed ellipticity is 0.999. When the ellipticity is 0, the Angle control is disabled. |
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Angle |
The orientation of the major axis of the apertures, in units of degrees. If the Ellipticity is 0, then the apertures are circular and the angle has no significance. |
FWHM Preferences, FWHM Measurements, Source Extraction Post Processing
