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Optimizing MG3 and MG4 files

Optimizing is a way of repurposing an image without having to reencode it. Optimize is MrSID-specific and offers special options for existing MG3 and MG4 files. Any MG3 or MG4 image can be optimized unless it was encoded with the ‑nonoptimizable switch. In additional to flat files, MrSID composite images can also optimized.

Optimizing operations do not decrement the data cartridge.

Optimizing operations include cropping and resampling (or downsampling).

For information on cropping, see Cropping an image.

Resampling

The switch ‑resample (sint) resamples an MG3 or MG4 file by a power of 2.

MG3 and MG4 files are crafted to include multiple resolutions to allow rapidly zooming in and out by factors of two (i.e., 2x, 4x, etc.)

Resampling allows you to reduce the file size by limiting the number of zoom levels included in the output file, at the expense of lower detail.

The number of zoom levels to remove is mapped to a “resampling factor.” For example, a resampling factor of two would remove one level and contain half as much detail as the original image. A resampling factor of four would remove two levels and contain one fourth of the detail of the original image.