MOPEX User's Guide - IRSA

Figure 8.17: Fine Res = 4. The coordinates of the shaded pixel are j = 2, k = 2.
8.4.3 Drizzle: Pixel Overlap Distribution
MOPEX User’s Guide
The output pixels values are computed using Eq.1, just like in the previous scheme. The
difference is that for this scheme (see Figure 8.18) the input pixels are projected onto the output
frame. The flux of an input pixel gets distributed among the output pixels it overlaps.
Each input pixel is shrunk by the factor Drizzle Factor (DRIZ_FAC in command-line namelists).
The values of the shrunken pixels are equal to the values of the original pixels. The shrunken
pixels are projected onto the output image frame. This would be extremely hard to implement
using scheme one, since then the overlap with the non-contiguous array of pixels would have to
be computed (see Figure 8.19). On the other hand scheme one has been shown to be faster by
~25% than scheme two in the case of no drizzle, Drizzle Factor = 1.
Note: When using the Drizzle option, several of the mosaicking steps are run twice. Firstly, a
linear interpolation is carried out so MOPEX can run the outlier rejection scheme. Once the
outlier rejection masks (RMasks) have been created, MOPEX returns to the Mosaic Interpolate
module and re-runs the interpolation with the Drizzle algorithm, masking out any pixels flagged
in the RMasks. Whe n using this option, do not include the Mosaic Re interpolate module in
the processing flow.
Basic Concepts in MOPEX 202
Image Interpolation