fast batch image resizer

I'm using IrfanView for converting 1 GB of tiff files to smaller GIF ones each night. Takes only some minutes.

A sample command woulöd look like this (I use this to convert pictures for my digital photo display)

"C:\Program Files (x86)\IrfanView\i_view32.exe" "C:\Pictures\Best\*.jpg" /resample=(720,540) /aspectratio /convert="C:\Temp\miniDisp\*_rsz.jpg"

This does resize all JPG files from C:\Picutres\Best\ to 720x540 and save them as C:\Temp\miniDisp\ OrgFilename_rsz.jpg.

The command line switches IrfanView understands can be found inside the online help (see Index - Command line options) or online here

Not sure how it will compare in the benchmark dept but you may want to give ImageMagick a try using the "convert" or "mogrify" tools. It sounds like it makes good use of 64 bit, number of cores and such.
All I know is that it is really powerful and feature full. I can resize in place or add options like resample filters and file type conversions.

mogrify -format jpg -filter Cubic -resize 20%x20% rgb-?.png

Check out these programs:

1. Batch Picture Resizer.
2. Image Resizer.

Resizing images using batch files: Batch Resize.

Parallel can be used to speed up batch conversions with imagemagick.

Shrink every *.jpg in a directory such that neither the height nor width is bigger than 1080 pixels:

parallel mogrify "{}" -resize 1080x1080 ::: *.jpg

Using convert to create seperate smaller files:

parallel convert "{}" -resize 1080x1080 "{.}-small.jpg" ::: *.jpg

Note that this applies to GNU parallel, not the version packaged in Debian's moreutils, which has a different syntax & less features. See the man page for more information on parallel.