(define (batch-scale 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))))

(let*
(
(max-length 480)
(image-width (car (gimp-image-width image)))
(image-height (car (gimp-image-height image)))
(scale-factor (/ max-length image-height))
(final-width (* scale-factor image-width))
(final-height (* scale-factor image-height))
)

(if (< image-height image-width)
(begin
(set! scale-factor (/ max-length image-width))
(set! final-width (* scale-factor image-width))
(set! final-height (* scale-factor image-height))
)
)

(gimp-image-scale image final-width final-height)
)
             
             (gimp-file-save RUN-NONINTERACTIVE
                             image drawable filename filename)
             (gimp-image-delete image))
           (set! filelist (cdr filelist)))))