You are here: Appendix B: File Sizes and Memory Usage > Calculating MrSID Area of Interest weight

Calculating MrSID Area of Interest weight

GeoExpress calculates the resultant image filesize as part of the encoding process, taking into account the user-defined compression ratios for inside and outside the Area of Interest. Selecting the Weight option allows you to specify Lossless compression or to set a target Compression Ratio for the Area of Interest. (The outside area will be encoded at the compression ratio specified in the job options.)

As an example, consider a 1-band (grayscale), 8-bit input image measuring 1000 × 1000 pixels. The user specifies compression for this image at 100:1. An Area of Interest measuring 100 × 100 pixels is then defined within the image, and the compression ratio inside the Area of Interest is set at 10:1.

Based on these dimensions and specifications, GeoExpress makes the following calculations:

GeoExpress then makes the following filesize calculations:

GeoExpress then calculates the overall compression ratio:

In order to calculate the overall target filesize for the encode process the compression ratio for the overall image is set to 91.73. The target filesize thus becomes:

The filesize of the output is reported in the Creating and viewing logs.