The optimizer is best-effort: any image it cannot process is left
unchanged in the output, which remains valid. Previously, an extraction
failure (e.g. an exotic colorspace pikepdf cannot transcode) was logged
with log.exception, printing a full traceback at ERROR level that alarmed
users even though nothing was wrong with the output (issue #846).
Trap such failures with a concise warning that the image was left
unchanged and the output is still valid, and demote the traceback to
debug verbosity for diagnosis.
James R. Barlow
58642d8411