Removing irregularly-shaped collars from images is basically the same task as cutting some desired item, like a person or a house, out of a photo, to eliminate the background and thus allowing the use of that item as clip art. That's a mess, exactly because of the irregularity and because of effects like JPEG halos, anti-aliasing of pixels and so on. That's why such work is mainly done manually, by hosts of graphics-editor assembly line workers. Indian contracting firms have a big presence in that business. 9 works with pixels procedurally, using expressions, scripts, and so on - not well suited to such manual workflow. Until 9 provides interactive tools like selecting a region of pixels with a polygonal "lasso", cutting and then pasting as a new image, a different tool, like 8, is the right approach. Even better is to drill back into the food chain that provided these images. When the original photo was shot, almost certainly there was no collar, just the pixels that made up the actual photo. Most likely, that collar got added at some step after the original photo was taken. The key is to get to the photo before somebody trashed it by adding a collar. Then there's no issue. It's like a lot of work in GIS: spending a little effort on getting clean data in the first place can save days or weeks of effort trying to repair data that's been altered into less convenient form.
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