To identify areas in your imagery that you do not want to include in the output mosaic, or in the color-balancing computation, you must first open the images in CATALYST Professional Focus and examine them individually.
For example, Figure 1 shows three sample images in Focus.
In Figure 1, some regions of the imagery contain significant cloud cover. To ensure that the color balancing of the mosaic is not skewed by clouds, the cloud-covered regions should be removed before performing the color-balancing operation. An exclusion mask defines the areas in the image that you want to exclude from the mosaic.
Areas other than cloud cover can also be considered as problem areas in your imagery. For example, the image may contain notably bright urban regions or significant shadows that can skew the results of the color balancing. Identifying such problem areas is the first step towards achieving better color balancing.