Batch Image Resizing from the GIMP command-line

The following TinyScheme (Script-Fu) script resizes one or more image files as specified with a file glob, and writes the resized image files into an output directory:

(define (scale-to-max-fileglob
         file-pattern
         out-dir
         newmax
         )
  (let* ((filelist (cadr (file-glob file-pattern 1))))
    (while (not (null? filelist))
      (let* ((in-file (car filelist))
             (image (car (gimp-file-load RUN-NONINTERACTIVE in-file in-file)))
             (drawable (car (gimp-image-get-active-drawable image)))
             (old-width (car (gimp-image-width image)))
             (old-height (car (gimp-image-height image)))
             (old-max (max old-width old-height))
             (new-width (round (/ (* old-width newmax) old-max)))
             (new-height (round (/ (* old-height newmax) old-max))))
        ;; http://tinyurl.com/7bvura2 states "... because saving undo
        ;; steps can be time and memory intensive" and so we don't
        ;; care about undo operations for batch runs:
        (gimp-image-undo-disable image)
        (gimp-image-scale image new-width new-height)
        (let ((out-file
               (string-append out-dir
                              ;; Insert a slash character if
                              ;; not already at the tail-end
                              ;; of out-dir:
                              (if (char=? #\/ (car (last (string->list out-dir))))
                                  ""
                                  "/")
                              ;; Take the basename of in-file which may be a fully-qualified path:
                              (car (last (strbreakup in-file "/"))))))
          ;; The print function does not show output on standard
          ;; output, so use gimp-message instead:
          (gimp-message (string-append "   scale-to-max-fileglob: scaling "
                                       in-file " into " out-file
                                       " with these dimensions: "
                                       (number->string new-width) "x" (number->string new-height)))
          (gimp-file-save RUN-NONINTERACTIVE image drawable out-file out-file))
        (gimp-image-delete image))
      (set! filelist (cdr filelist)))))

Store this into ~/.gimp-2.6/scripts/batch-resize.scm and the definition of scale-to-max-fileglob will load into all future gimp sessions.


Example run: This was executed using GIMP 2.6 on a 64-bit Debian Linux machine.  The "script-fu-Warning" is coming from the gimp-message function:



user@somehost:/tmp/images_dir$ time gimp -i -b '(begin (scale-to-max-fileglob "*.jpg" "outdir" 1000) (gimp-quit 0))'

script-fu-Warning:    scale-to-max-fileglob: scaling 2012-05-19_16-43-42_676.jpg into outdir/2012-05-19_16-43-42_676.jpg with these dimensions: 562x1000

script-fu-Warning:    scale-to-max-fileglob: scaling 2012-05-19_16-44-35_210.jpg into outdir/2012-05-19_16-44-35_210.jpg with these dimensions: 562x1000

script-fu-Warning:    scale-to-max-fileglob: scaling 2012-05-19_16-41-21_785.jpg into outdir/2012-05-19_16-41-21_785.jpg with these dimensions: 1000x562

script-fu-Warning:    scale-to-max-fileglob: scaling 2012-05-19_16-44-02_760.jpg into outdir/2012-05-19_16-44-02_760.jpg with these dimensions: 1000x562

script-fu-Warning:    scale-to-max-fileglob: scaling 2012-05-19_16-45-34_771.jpg into outdir/2012-05-19_16-45-34_771.jpg with these dimensions: 562x1000

script-fu-Warning:    scale-to-max-fileglob: scaling 2012-05-19_16-43-15_141.jpg into outdir/2012-05-19_16-43-15_141.jpg with these dimensions: 562x1000

script-fu-Warning:    scale-to-max-fileglob: scaling 2012-05-19_16-42-39_886.jpg into outdir/2012-05-19_16-42-39_886.jpg with these dimensions: 562x1000

script-fu-Warning:    scale-to-max-fileglob: scaling 2012-05-19_16-45-13_128.jpg into outdir/2012-05-19_16-45-13_128.jpg with these dimensions: 562x1000

script-fu-Warning:    scale-to-max-fileglob: scaling 2012-05-19_16-42-52_376.jpg into outdir/2012-05-19_16-42-52_376.jpg with these dimensions: 562x1000

script-fu-Warning:    scale-to-max-fileglob: scaling 2012-05-19_16-41-49_429.jpg into outdir/2012-05-19_16-41-49_429.jpg with these dimensions: 562x1000

script-fu-Warning:    scale-to-max-fileglob: scaling 2012-05-19_16-42-08_196.jpg into outdir/2012-05-19_16-42-08_196.jpg with these dimensions: 562x1000

script-fu-Warning:    scale-to-max-fileglob: scaling 2012-05-19_16-41-54_552.jpg into outdir/2012-05-19_16-41-54_552.jpg with these dimensions: 562x1000

script-fu-Warning:    scale-to-max-fileglob: scaling 2012-05-19_16-42-34_497.jpg into outdir/2012-05-19_16-42-34_497.jpg with these dimensions: 562x1000



real    0m16.179s
user    0m13.229s
sys    0m2.236s



The above code was cobbled together from these sources:

1. Christopher Campbell's blog: Batch image scaling with Gimp
2. TinySCHEME Version 1.40 Manual is rather skimpy so you may desire to refer to The Racket Reference instead.
3. Gimp Batch Mode Introduction