PNG optimisation tools

Question

A while back I used a PNG optimisation service called (I think) "smush it". You fed it a weblink and it returned a zip of all the PNG images with their filesizes nicely, well, smushed...

I want to implement a similar optimisation feature as part of my website's image upload process; does anyone know of a pre-existing library (PHP or Python preferably) that I can tap into for this? A brief Google has pointed me towards several command line style tools, but I'd rather not go down that route if possible.

Answer 1

As long as your PHP is compiled with GD2 support (quite common nowadays):

<?php
$image = imagecreatefromstring(file_get_contents('/path/to/image.original.png'));
imagepng($image, '/path/to/image.smushed.png', 9);

This will read in any image format GD2 understands (not just PNG) and output a PNG gzipped as the maximum compression level without sacrificing quality.

It might be of less use today than years ago though; most image editors already do this, since gzipping doesn't cost as much CPU-wise as it used to.

Answer 2

Have you heard of PNGCrush? You could check out the source, part of PNG and MNG Tools at SourceForge, and transcribe or wrap it in Python.

Answer 3

I would question the wisdom of throwing away other chunks (like gAMA and iCCP), but if that's what you want to do it's fairly easy to use PyPNG to remove chunks:

#!/usr/bin/env python
import png
import sys

input=sys.stdin
out=sys.stdout

def critical_chunks(chunks):
    for type,data in chunks:
        if type[0].isupper():
            yield type,data

chunks = png.Reader(file=input).chunks()
png.write_chunks(out, critical_chunks(chunks))

the critical_chunks function is essentially filtering out all but the critical PNG chunks (the 4 letter type for a critical chunk starts with an uppercase letter).

Answer 4

Execute with PHP this command line tools

  pngcrush -rem gAMA -rem cHRM -rem iCCP -rem sRGB -brute -l 9 -max -reduce -m 0 -q IMAGE
  optipng -o7 -q pngout.png
  pngout pngout.png -q -y -k0 -s0
  advpng -z -4 pngout.png > /dev/null

• pngcrush
• OptiPNG
• pngout
• advpng