GeoExpress offers two methods, the weight and mask methods, for encoding an area of interest with MG3 or MG4 as the output format.
TIP:Area of interest encoding of MG3 and MG4 images can be done more quickly if the images were originally encoded as optimizable. For more information, see Optimizable.
NOTE: Area of interest encoding in MG3 format automatically uses the 2-Pass optimizer, even if its check box on the Format-Specific tab of the Advanced Job Options dialog box has not been selected. For more information, see 1-Pass or 2-Pass Optimizer.
The weight method is the default for encoding areas of interest with GeoExpress. (This is not to be confused with the weight parameter in the advanced job options.) The parameters for using the weight method differ depending on the output format. MG3 and MG4 require the user to enter 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. Selecting the weight radio button enables you to specify an encode ratio for the area of interest or select the Lossless check box. The outside area will be encoded at the compression ratio specified in the Job Options dialog. These ratios are used in a calculation of the overall image compression.
The calculated filesize appears on the Properties tab for the image once you close the Area of Interest dialog box.
The mask method renders either the foreground or the background as a solid color, completely obscuring (actually removing) the underlying image data.
The mask method only applies to encode jobs and is not available for optimizations.
To mask any area(s) inside the AOI polygon(s) (foreground), select Mask Inner.
To mask any region(s) outside the AOI polygon(s), select Mask Outer.
To specify or change the mask color, select either Mask Inner or Mask Outer, then click Mask Color. The AOI Mask Color dialog box appears.
By default the mask color is black. Black drives all pixel values to the minimum supported value (usually zero), while white drives all pixel values to the maximum supported value (e.g. 255 for an 8-bit image). You can also specify a custom 8-bit RGB color value.
To specify a custom 8-bit RGB color value, select the Custom option and fill in the red, green and blue values.
The compression ratios for the inside and outside of the area of interest are reported in the GeoExpress log file after you run the area of interest job. For more information on log files, see Viewing and Using Log Information.