unpack_thumb unpacks previews instead

Upon using ExifRead (https://pypi.org/project/ExifRead/) to processes exif metadata from an image and using that to extract the Jpeg Thumbnail, we came to know that the extract_thumb method, instead of extracting the Jpeg Thumbnail, will extract the Jpeg Preview of a RAW image. Is this a desired behavior and if so, is there a way to extract the actual Jpeg Thumbnail from the image?

Also, in case the Jpeg Preview is missing, will Libraw report and error or extract the Jpeg Thumbnail instead?

More information about this issue can be found at the discussion here: https://github.com/letmaik/rawpy/issues/96

Thanks!

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unpack_thumb() provides

unpack_thumb() provides largest available thumbnail/preview/whatever-it-called.

-- Alex Tutubalin