Extended sources are also identified if the parameter detectextended is set. The photometry of an extended source is made by adding all the counts received in an elliptical area and the background is measured in an annulus, as for point sources. Coincidence loss correction is applied by considering that every pixel is a point like source.
Since SAS v9.0, omdetect can be used on final mosaiced or stacked images in order to find fainter, previously undetected sources.
A skyimage (SIMAGE.FIT) is generated from the input image, by resampling the image, applying the distortion correction and north aligning the image. No other correction is applied to this image, i.e. coincidence losses and deadtime are not corrected. The skyimage provides the most accurate positional information of an image in the OM image data processing chain. Note that IMAGE_ has no distortion correction and therefore its positional information is less accurate than in the SIMAGE.