Efficiently generating thumbnails with ImageMagick and convert

Question

I\'m looking to efficiently generate various sized thumbnails with ImageMagick\'s convert utility in Python. Some of my image files are quite large (~15MB JPGs).

One

Answer 1

I'm thumbnailing ~50MB JPG files. The one option which made the biggest difference (~5x speedup) was "-define jpeg:size 128x128" before the input filename. The example given here:

http://www.imagemagick.org/Usage/formats/#jpg_read

...made a huge difference:

convert -define jpeg:size=128x128 jpeg_large.jpg -thumbnail 64x64  jpeg_thumbnail.jpg

-define jpeg:size allows ImageMagick to read in only as much data as it needs from disk, which greatly reduces load time for very large images.

As the linked page suggests, use a jpeg:size= of twice your final thumbnail size to avoid aliasing.

The -thumbnail option, described here:

http://www.imagemagick.org/Usage/resize/#thumbnail

...samples and strips the image, further speeding up the process.