Comments on: Optimize all your PNG and JPEG images with one command using imgopt

By: Optimise your site with scheduled image optimisation - G-Williams

Optimise your site with scheduled image optimisation - G-Williams — Mon, 19 Sep 2011 14:59:32 +0000

[...] it a go and let me know what you think. I found the script here - http://lyncd.com/2009/03/imgopt-lossless-optimize-png-jpeg/. I should clarify that the below instructions are for a 64bit CentOS 5.5 installation so may [...]

By: Jon

Jon — Sun, 06 Feb 2011 18:09:16 +0000

Excellent work! An easy to use and indispensable tool for any web developer.

By: Why I Didn’t Try To Win Webperf Contest 2010 | Razor Fast

Why I Didn’t Try To Win Webperf Contest 2010 | Razor Fast — Tue, 07 Dec 2010 02:15:21 +0000

[...] as much as possible while avoiding noticeable artifacts. All PNGs were processed with the imgopt script, which passes them through 3 different optimizers. The eventual goal was to merge them into a [...]

By: Ariel

Ariel — Tue, 29 Jun 2010 12:39:46 +0000

So I ran a full test on a bunch of images (I ran the original twice, and the new one twice).

I reordered the commands to:

advpng -z0f
pngout
optipng
advpng

The results were not as dramatic as I thought they would be. It seems that the file (I picked randomly) just so happened to be one that changed a lot.

Most of the files were unchanged, a couple got larger (but usually only by 4 bytes). And some got about 10-20% smaller.

Overall though I think it’s a win.

BTW thanks for this script.

By: Ariel

Ariel — Tue, 29 Jun 2010 12:04:25 +0000

It happened when I hit control-c. It’s possible to catch signals in a shell script using the trap command.

By: Ariel

Ariel — Tue, 29 Jun 2010 11:01:00 +0000

A small bug: When I ran it on a directory it left a tmp file behind.

By: Ariel

Ariel — Tue, 29 Jun 2010 10:56:47 +0000

I tested a bit:

Original file: 4398 (from gimp)
optipng: no change
After advpng: 1723
pngout: no change

If I do pngout first though:

pngout: 2466
advpng: 1303

In fact, I think you should first expand the file with advpng -z0f to decompress it, then let optipng work on it – and this time give it a chance to actually optimize it, without being fooled by the strong compression, and pngout, and then advpng.

Another test (same file):

optipng: no change, file size 4398
advpng -z0f
optipng: 1769
pngout: no change
advpng: 1723

Next test:

advpng -z0f
pngout: 2466
advpng: 1303

Optipng actually hurt the compression of pngout!

Final try:

advpng -0zf
pngout: 2466
optipng: 1353
advpng: 1303

At least for this file, the best order is exactly the opposite of what you have.

By: Ariel

Ariel — Tue, 29 Jun 2010 10:32:59 +0000

Since advpng just recompresses the file, but does not change the structure of the png in any way, shouldn’t it go last (or at least after optipng)?

Otherwise advpng compresses the image really well, then when optipng goes to work on it, it refuses to save it because its compression does not do as well (so the file _appears_ to be bigger) – even though it actually managed to optimize the png structure of the file.

By: Xinjiang Lu

Xinjiang Lu — Fri, 23 Apr 2010 17:04:04 +0000

I just tested this script. Interesting, for some images, pngout+imgopt produces a smaller image (~8% reduced) than any other combination.

By: Rob Scott

Rob Scott — Tue, 23 Mar 2010 12:21:19 +0000

Found this looking for something slightly different, but, as ever, this looks like a better script than I was looking for :) Will be testing this on a couple of user-generated sites as that’s where image files start to grow into huge beasts, coders should be doing this before putting them in!

(Actually, that’s what I was looking for, but not a retrospective “run on a whole folder or set of folders” version like this, but a script to optimize images on the fly as they are uploaded by user. Pretty sure this is a good starting point for both!)