The task will only handle images which are a tangent plane projection of the sky, for example those created from the X and Y columns of EPIC event lists using evselect. Images from the optical monitor, which in their raw form contain a significant amount of distortion, could in principle be mosaiced after reprojection to the tangent plane projection.
The output image is the additive mosaic of the input images, in other words no average is performed. If the input image list is matched with a corresponding list of exposure maps, these exposure maps are additively mosaiced in parallel, then the output image is divided by the mosaiced exposure map. This approach is preferable to mosaicing exposure corrected images, as it helps avoid problems of poor counting statistics in areas of low exposure. Binary masks can be simulated by providing exposure images which have a pixel values of zero or one.
The output pixel size (in degrees) and world-coordinate system (WCS) reference coordinate for the output image are set to those of the first input image. The task can read images in any of the dal-supported numeric data types. If all the input images have the same data type, the output image also has that type; otherwise the output is written in real64.