Fix clipping logic in preview image scaling

[bhilbert4]

Resolves #1009

This PR fixes a flaw in the logic of the pixel clipping when determining scaling limits for preview images. Previously the number of pixels to be clipped was the user-input percentage of the total number of non-science pixels. With this change, it is now the user-input percentage of the number of non-science pixels with finite signal.

[pep8speaks]

Hello @bhilbert4, Thank you for updating !

• In the file jwql/utils/preview_image.py:

Line 50:1: E402 module level import not at top of file
Line 51:1: E402 module level import not at top of file
Line 52:1: E402 module level import not at top of file
Line 456:5: E303 too many blank lines (2)

Comment last updated at 2022-07-28 19:36:53 UTC

[bhilbert4]

I also just added in here a small tweak so that generate_preview_images only looks in visit-specific subdirectories (e.g. jw01234001001) for files to make preview images for. Some programs also have a "pre-image" subdirectory which contain files that we don't need to pay attention to (and which crash the filename parser), and others have an "L3" subdirectory, which contain level 3 products. For the moment we don't pay attention to these, although it might be nice in the future to make preview images for them.