Resize images in directory

If you want to do it programatically, which I assume is the case, use PIL to resize e.g.

newIm = im.resize((newW, newH)

then save it to same file or a new location.

Go through the folder recursively and apply resize function to all images.

I have come up with a sample script which I think will work for you. You can improve on it: Maybe make it graphical, add more options e.g. same extension or may be all png, resize sampling linear/bilinear etc

import os
import sys
from PIL import Image

def resize(folder, fileName, factor):
    filePath = os.path.join(folder, fileName)
    im = Image.open(filePath)
    w, h  = im.size
    newIm = im.resize((int(w*factor), int(h*factor)))
    # i am saving a copy, you can overrider orginal, or save to other folder
    newIm.save(filePath+"copy.png")

def bulkResize(imageFolder, factor):
    imgExts = ["png", "bmp", "jpg"]
    for path, dirs, files in os.walk(imageFolder):
        for fileName in files:
            ext = fileName[-3:].lower()
            if ext not in imgExts:
                continue

            resize(path, fileName, factor)

if __name__ == "__main__":
    imageFolder=sys.argv[1] # first arg is path to image folder
    resizeFactor=float(sys.argv[2])/100.0# 2nd is resize in %
    bulkResize(imageFolder, resizeFactor)

How about using mogrify, part of ImageMagick? If you really need to control this from Perl, then you could use Image::Magick, Image::Resize or Imager.

Can it be in shell?

mkdir resized
for a in *.jpg; do convert "$a" -resize 60% resized/"$a"; done

If you have > 1 core, you can do it like this:

find . -maxdepth 1 -type f -name '*.jpg' -print0 | xargs -0 -P3 -I XXX convert XXX -resize 60% resized/XXX

-P3 means that you want to resize up to 3 images at the same time (parallelization).

If you don't need to keep originals you can use mogrify, but I prefer to use convert, and then rm ...; mv ... - just to be on safe side if resizing would (for whatever reason) fail.