There are three 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 based on the nominal dimensions of the image, which is:
Width in pixels × height in pixels × number of bands (red, blue, green, infrared, etc.) × bit depth of the pixel
- 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 installed with GeoExpress. Here is an example of the mrsidgeoinfo command:
mrsidgeoinfo C:/testimages/image.sidThe compression ratio (calculated with and without an alpha band if there is one) is reported in the results under “basic image info”
- Install GeoViewer and use it to open your image. Right-click the image name and select "View layer metadata" in the drop-down. Click on Image properties to view the compression ratio.