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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.