batch_monochrome.scm

(define (batch-monochrome 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)))
             (LUMINOSITY-FORMULA 1))
        ; do stuff here
        (gimp-desaturate-full drawable LUMINOSITY-FORMULA)
        (gimp-file-save RUN-NONINTERACTIVE
                        image drawable filename filename)
        (gimp-image-delete image))
      (set! filelist (cdr filelist)))))