(Updated 2008-01-23)
Shortly after acquiring a digital camera, I felt the need to be able to make the images available via the Internet. The standard size of the images was too large (at over 0.5MB) to make downloading convenient. I therefore needed a process which could turn the images (automatically) into a reasonable size.
The Gimp seemed the first choice. I was pleased to learn that the Gimp's script language was Scheme, a variant of Lisp. Since I'd been learning Common Lisp for a little while (via Object Oriented Common Lisp by Stephen Slade), it seemed a happy coincidence.
Scheme is a little different to CL, but that wasn't really an issue for the size of program I wanted to write; it's the usual grappling with a new, undigested command set. After much googling, trial and error, I arrived at the following gimp script. It produces a cut-down image and a thumbnail from the original jpeg file.
;;;; Thumbnail Creation Gimp script
;;;;
;;;; To run this from the command prompt:
;;;; gimp -c -d -i -b '(script-fu-thumbnail "file.jpg" tw th fw fh)' -b '(gimp-quit 0)'
;;;;
(define (script-fu-thumbnail filename t-width t-height f-width f-height)
(let* ((img 0) (drw 0) (fileparts (strbreakup filename ".")))
;; car needed here because gimp functions return values as lists
(set! img (car (file-jpeg-load 1 filename filename)))
;; set image resolution to 72dpi
(gimp-image-set-resolution img 72 72)
;; create 'full-size' image
(gimp-image-scale img f-width f-height)
;; also flatten image to reduce byte storage even further
(set! drw (car (gimp-image-flatten img)))
;; save at quality level of .75 (gimp default) - saves storage
(file-jpeg-save 1 img drw
(string-append (car fileparts) "-f.jpg")
(string-append (car fileparts) "-f.jpg")
.75 0 0 0 " " 0 1 0 1)
;; create thumbnail image
(gimp-image-scale img t-width t-height)
(file-jpeg-save 1 img drw
(string-append (car fileparts) "-t.jpg")
(string-append (car fileparts) "-t.jpg")
.75 0 0 0 " " 0 1 0 1)
))
(script-fu-register "script-fu-thumbnail"
"<Toolbox>/Xtns/Script-Fu/Utils/Thumbnail..."
"Thumbnail"
"Mark Willson"
"Mark Willson"
"Dec 2003"
""
SF-VALUE "Image Name" " "
SF-VALUE "Thumbnail Width" "256"
SF-VALUE "Thumbnail Height" "192"
SF-VALUE "Full Width" "1024"
SF-VALUE "Full Height" "766")
Here's another version of the script, modifications by Martin Bradley, which preserves the aspect ratio of the original image.
;;;; Thumbnail (Keep Aspect Ratio) Gimp script
;;;;
;;;; To run this from the command prompt:
;;;; gimp -c -d -i -b '(script-fu-thumbnail-kar
;;;; "file.jpg" thumb-width full-width)' -b '(gimp-quit 0)'
;;;;
(define (script-fu-thumbnail-kar filename t-width f-width)
(let* ((img 0) (drw 0) (fileparts (strbreakup filename ".")) )
;; car needed here because gimp functions return values as lists
(set! img (car (file-jpeg-load 1 filename filename)))
;; set image resolution to 72dpi
(gimp-image-set-resolution img 72 72)
;; determine original aspect ratio and preserve w.r.t width required
(let* ((original-width (car (gimp-image-width img)))
(original-height (car (gimp-image-height img)))
(t-height (* original-height (/ t-width original-width)))
(f-height (* original-height (/ f-width original-width))))
;; create 'full-size' image
(gimp-image-scale img f-width f-height)
;; also flatten image to reduce byte storage even further
(set! drw (car (gimp-image-flatten img)))
;; save at quality level of .75 (gimp default) - saves storage
(file-jpeg-save 1 img drw
(string-append (car fileparts) "-f.jpg")
(string-append (car fileparts) "-f.jpg")
.75 0 0 0 " " 0 1 0 1)
;; create thumbnail image
(gimp-image-scale img t-width t-height)
(file-jpeg-save 1 img drw
(string-append (car fileparts) "-t.jpg")
(string-append (car fileparts) "-t.jpg")
.75 0 0 0 " " 0 1 0 1))))
(script-fu-register "script-fu-thumbnail-kar"
"<Toolbox>/Xtns/Script-Fu/Utils/Thumbnail (KAR)..."
"Process Image"
"Mark Willson/Martin Bradley"
"Mark Willson/Martin Bradley"
"Jan 2008"
""
SF-VALUE "Image Name" " "
SF-VALUE "Thumbnail Height" "192"
SF-VALUE "Full Height" "766")
As you can see, it's not exactly easy to kick off the gimp script from the command line, so here's a shell script to drive it. This script invokes the original script-fu-thumbnail, but it is a simple matter to modify it to use the alternate version.
#!/bin/bash
# SYNOPSIS
# prjpg file [file ...]
#
# DESCRIPTION
# Script to produce 'thumbnails' and images for web consumption
#
# <prefix>-t.jpg = thumbnail (currently set to 256x192)
# <prefix>-f.jpg = full image (currently set to 800x600)
#
# MODIFICATION HISTORY
# Mnemonic Rel Date Who
# PRJPG 1.0 01Feb04 mpw
# Written.
# PRJPG 1.1 30May05 mpw
# Revised argument interface to use list of files
# PRJPG 1.2 08Feb10 mpw
# -b only takes one gimp expression, hence "(gimp-quit 0)" prefixed by -b
# Process files via the Gimp
for x in $*
do
if [ -r $x ]; then
echo "..processing $x"
nice -n 19 gimp -c -d -i -b "(script-fu-thumbnail \"$x\" 256 192 800 600)" -b "(gimp-quit 0)"
else
echo "$0: unable to read $x"
fi
done
