(define (batch-adjust-color-levels pattern)
  (let* ((filelist (cadr (file-glob pattern 1))))
    (while (not (null? filelist))
           (let* ((filename (car filelist))
                  (image (car (gimp-file-load RUN-NONINTERACTIVE filename filename)))
                  (drawable (car (gimp-image-get-active-layer image))))
             (gimp-levels-stretch drawable)
             (gimp-file-save RUN-NONINTERACTIVE image drawable filename filename)
             (gimp-image-delete image))
           (set! filelist (cdr filelist)))))