GeoExpress offers two methods, the weight and mask methods, for encoding an area of interest with MG3 as the output format. For a table describing the area of interest encoding switches, see Specifying an Area of Interest.
NOTE: Area of interest encoding in MrSID format automatically uses the 2-pass optimizer.
The weight method is not to be confused with the “weight” parameter in the advanced encoding options. Also, area of interest encoding using the weight method functions differently for MrSID and JP2 output. In MrSID encoding the weight method requires the user to input a compression ratio for the area of interest. 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 (see Inner and Outer Areas). These ratios are used in a calculation of the overall image compression. The actual output is reported on the GeoExpress log file. For more information, see Calculating MrSID Area of Interest Weight.
To use the weight method, specify a compression ratio for the data inside the area of interest by using the -aoicr (or –aoicrlossless) switch. The outside area will be encoded at the compression ratio specified for the entire image (in the –cr switch).
The mask method removes the foreground or the background (see Inner and Outer Areas) and replaces it with a solid color. The mask method only applies to encode jobs and is not available for optimizations.
To mask the foreground areas use the -aoimaskinner switch.
To mask the background areas use the -aoimaskouter switch. These switches cannot be used with any other AOI method (-aoicr, -aoilossless, -aoishiftinner, -aoishiftouter, -aoimaskouter, -aoiweightinner, -aoiweightouter).
The default color for the masked areas is black. You may change this using the -aoimaskcolor switch in conjunction with either the -aoimaskinner or the -aoimaskouter switch.
Acceptable values for the -aoimaskcolor parameter are as follows:
black – uses the minimum sample value
white – uses the maximum sample value
RRR_GGG_BBB – uses a custom 8-bit RGB color
Default value is black.