F070105 - How do I find the compression ratio used to encode a MrSID image?

There are two ways to find the compression ratio that was used to encode a MrSID image.

• To calculate the compression ratio yourself, divide the input image size by the input file size (both are shown on the GeoExpress properties tab). The input image size is the same as the “nominal” image size, which is:
  width x height x number of bands x number of samples
  As an example, if you divide an input image size of 5 GB by an input file size of 256 MB, the result is 20, or a compression ratio of 20:1.

• Alternatively, you may use the command line utility mrsidgeoinfo, which is intstalled with GeoExpress. Here is an example of the mrsidgeoinfo command:
  mrsidgeoinfo C:/testimages/image.sid
  The compression ratio (calculated with and without an alpha band if there is one) is reported in the results under “basic image info”

This article was last updated or verified on 9 October 2012.