MinMed masking
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MultiDrizzle implements a the 'minmed' algorithm for creating
the median image, which combines a minimum image with a clipped median.
Behavior: By default, the highest input pixel gets clipped by this method, resulting in an output where regions with only input from 1 image gets masked out, instead of being retained as the minimum value. Thus, only regions where more than 1 image overlaps gets retained in the output median image when using 'minmed'. Workaround: None. |
Missing Pixels |
MultiDrizzle computes the
parameters necessary for running 'drizzle' using PyDrizzle. The
user can also specify the RA/Dec position of the output frame. Behavior: Some pixels get reported as 'dropped' during the single and final drizzle steps. If a user specifies the RA/Dec, MultiDrizzle will shift the images accordingly. This situation has been improved significantly, but it still can underestimate the final output size for this situation resulting in dropped pixels/rows. Workaround: A new output size can be specified which will be large enough to accomodate the entire output frame, if significant data is lost. |
Zero Exposure Time Images
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MultiDrizzle performs all image combination in units of
electrons per second, requiring (in most cases) conversion using the
exposure time. However, some associations include images where the
exposure time gets reported as 0.0 seconds. Behavior: All input images with zero exposure time are noted, reported to the user, then ignored for all MultiDrizzle processing. Workaround: The user can verify whether there is any valid data in the zero-exposure time input image. If the image contains useful data, the EXPTIME keyword in each SCI extension of that input image can be updated with a non-zero value that best approximates the actual exposure time used. |
Questions? Contact help@stsci.edu
26 February 2008