The following image format is recommended and used by big web sites such as Google / Yahoo / Amazon / Facebook etc:
- PNG file format is recommended for web.
- GIF file format is recommended for small size images.
- JPG file format is recommended for high resolution photographic-style images.
- Do not use BMPs or TIFFs.
Say hello to optipng
You need to use a tool called optipng. It is a PNG optimizer that recompresses image files to a smaller size, without losing any information. This program also converts external formats (BMP, GIF, PNM and TIFF) to optimized PNG, and performs PNG integrity checks and corrections. This tool can be installed on any server powered by Unix or Linux operating systems.
Installation
First, turn on EPEL repo and type the following yum command to install optipng:
## ** first enable epel repo on centos 7 ** ##
# yum install epel-release
# yum install optipng
Sample outputs:
Loaded plugins: auto-update-debuginfo, protectbase, rhnplugin 0 packages excluded due to repository protections Setting up Install Process Resolving Dependencies --> Running transaction check ---> Package optipng.x86_64 0:0.6.4-1.el6 will be installed --> Finished Dependency Resolution Dependencies Resolved =============================================================================== Package Arch Version Repository Size =============================================================================== Installing: optipng x86_64 0.6.4-1.el6 epel 82 k Transaction Summary =============================================================================== Install 1 Package(s) Total download size: 82 k Installed size: 181 k Is this ok [y/N]: y Downloading Packages: optipng-0.6.4-1.el6.x86_64.rpm | 82 kB 00:00 Running rpm_check_debug Running Transaction Test Transaction Test Succeeded Running Transaction Installing : optipng-0.6.4-1.el6.x86_64 1/1 Verifying : optipng-0.6.4-1.el6.x86_64 1/1 Installed: optipng.x86_64 0:0.6.4-1.el6 Complete! |
Debian and Ubuntu/Mint Linux user type the following apt-get command to install the same:
$ sudo apt-get install optipng
Reading package lists... Done Building dependency tree Reading state information... Done The following NEW packages will be installed: optipng 0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded. Need to get 89.0 kB of archives. After this operation, 212 kB of additional disk space will be used. Get:1 http://archive.ubuntu.com/ubuntu/ trusty/main optipng amd64 0.6.4-1build1 [89.0 kB] Fetched 89.0 kB in 0s (419 kB/s) Selecting previously unselected package optipng. (Reading database ... 16090 files and directories currently installed.) Preparing to unpack .../optipng_0.6.4-1build1_amd64.deb ... Unpacking optipng (0.6.4-1build1) ... Setting up optipng (0.6.4-1build1) ...
How do I use optipng command?
The syntax is:
optipng file optipng [options] file optipng [options] input.png |
My sample test.png image:
To display png image size, type, and compression info, enter:
$ pnginfo -t test.png
Sample outputs:
test.png (tiffinfo compatible labels)...
Image Width: 1164 Image Length: 911
Bits/Sample: 8
Samples/Pixel: 3
Pixel Depth: 24
Colour Type (Photometric Interpretation): RGB
Image filter: Single row per byte filter
Interlacing: No interlacing
Compression Scheme: Deflate method 8, 32k window
Resolution: 0, 0 (unit unknown)
FillOrder: msb-to-lsb
Byte Order: Network (Big Endian)
Number of text strings: 1 of 9
Software (xTXt deflate compressed): Shutter
Use ls command to see file size:
$ ls -lh test.png
Sample outputs:
-rw-r--r-- 1 vivek vivek 279K Nov 29 00:10 test.png
Use optipng optimization program as follows:
$ cp test.{png,bak}
$ optipng test.png
Sample outputs:
OptiPNG 0.6.4: Advanced PNG optimizer. Copyright (C) 2001-2010 Cosmin Truta. ** Processing: test.png 1164x911 pixels, 3x8 bits/pixel, RGB Input IDAT size = 284778 bytes Input file size = 285286 bytes Trying: zc = 9 zm = 8 zs = 0 f = 0 IDAT size = 215274 Selecting parameters: zc = 9 zm = 8 zs = 0 f = 0 IDAT size = 215274 Output IDAT size = 215274 bytes (69504 bytes decrease) Output file size = 215374 bytes (69912 bytes = 24.51% decrease) |
File size is reduced by 24.51%:
$ ls -lh test.png
Sample outputs:
-rw-r--r-- 1 vivek vivek 211K Nov 29 02:40 test.png
You can verify the quality of both images (click to enlarge):
Optimized test.png file ensures that it loads faster for users on slow connections. It will also save 24.51% bytes per image view in terms of both network bandwidth and storage. According to Google:
You should see a benefit for any image file that can be reduced by 25 bytes or more (less than this will not result in any appreciable performance gain).
How do I optimize files in bulk?
Use a bash for loop as follows:
#!/bin/bash cd /path/to/png/storage/2010/01/c/ mkdir optimized ## store optimized images in optimized directory ## ## Keep file system permission and make a backup of original PNG (see options below) ## for i in *.png; do optipng -o5 -quiet -keep -preserve -dir optimized -log optipng.log "$i"; done |
You need to make changes to your code. For example, url path to optimize url will be as follows:
http://s0.cyberciti.org/foo/bar/optimized/test.png
Alternatively, you can overwrite existing PNG images:
#!/bin/bash cd /path/to/png/storage/2010/01/c/ ## Overwrite images ## ## Keep file system permission and make a backup of original PNG (see options below) ## for i in *.png; do optipng -o5 -quiet -keep -preserve -log optipng.log "$i"; done |
Next, purge all images from your CDN account. See how to purge old images / invalidating object from cloud front for more information.
A note about processing *.png in all sub-directories
Use the find command as follows (make a backup of all images):
cd /var/www/html/uploads/ find . -type f -iname "*.png" -print0 | xargs -I {} -0 optipng -o5 -quiet -keep -preserve -log optipng.log "{}" |
Options
General options:
-fix enable error recovery
-force enforce writing of a new output file
-keep keep a backup of the modified files
-preserve preserve file attributes if possible
-quiet quiet mode
-simulate simulation mode
-snip cut one image out of multi-image or animation files
-out <file> write output file to <file>
-dir <directory> write output file(s) to <directory>
-log <file> log messages to <file>
-- stop option switch parsing
Optimization options:
-f <filters> PNG delta filters (0-5) default 0,5
-i <type> PNG interlace type (0-1) default <input>
-zc <levels> zlib compression levels (1-9) default 9
-zm <levels> zlib memory levels (1-9) default 8
-zs <strategies> zlib compression strategies (0-3) default 0-3
-zw <window size> zlib window size (32k,16k,8k,4k,2k,1k,512,256)
-full produce a full report on IDAT (might reduce speed)
-nb no bit depth reduction
-nc no color type reduction
-np no palette reduction
-nx no reductions
-nz no IDAT recoding
Optimization details:
The optimization level presets
-o0 <=> -o1 -nx -nz
-o1 <=> [use the libpng heuristics] (1 trial)
-o2 <=> -zc9 -zm8 -zs0-3 -f0,5 (8 trials)
-o3 <=> -zc9 -zm8-9 -zs0-3 -f0,5 (16 trials)
-o4 <=> -zc9 -zm8 -zs0-3 -f0-5 (24 trials)
-o5 <=> -zc9 -zm8-9 -zs0-3 -f0-5 (48 trials)
-o6 <=> -zc1-9 -zm8 -zs0-3 -f0-5 (120 trials)
-o7 <=> -zc1-9 -zm8-9 -zs0-3 -f0-5 (240 trials)
The libpng heuristics
-o1 <=> -zc9 -zm8 -zs0 -f0 (if PLTE is present)
-o1 <=> -zc9 -zm8 -zs1 -f5 (if PLTE is not present)
The most exhaustive search (not generally recommended)
[no preset] -zc1-9 -zm1-9 -zs0-3 -f0-5 (1080 trials)
Examples:
optipng file.png (default speed)
optipng -o5 file.png (moderately slow)
optipng -o7 file.png (very slow)
optipng -i1 -o7 -v -full -sim experiment.png |
Other png optimization tools for Linux / Unix
Debian / Ubuntu Linux and other operating *nix based systems can use the following tools for the same purpose:
- pngcrush – optimizes PNG (Portable Network Graphics) files.
- pngnq – tool for optimizing PNG (Portable Network Graphics) images. It is a tool for quantizing PNG images in RGBA format.
- pngquant – PNG (Portable Network Graphics) image optimising utility. It is a command-line utility for converting 24/32-bit PNG images to paletted (8-bit) PNGs.
Recommended readings:
- A guide to PNG optimization.
- Visit optipng home page to grab the latest version.
- Analyze and optimize your website with PageSpeed tools.
- 6 Tools To Find Out Website Load Speed.
8 comment
This is great, thanks for sharing Vivek.
Hi,
Thanks for very nice article…
Fine topic too, nicely done, THX Vivek. & KUTGW.
Thanks for the useful command.
Instead of the for I’ve used a find, so it can scan all the subdir:
find /path/to/myuploads/ -name *.png -exec optipng -o5 -quiet -keep -preserve -log /tmp/optipng.log '{}' \;I can’t tell you how many code snippets / tutorials I already use on your site. Whenever I’m searching for something online and I see your site appear in the search results, I already know before viewing the content that whatever I need done will surely work when you’re the one writing it!
Seriously, this is going to save me so much time now….I used to run PageSpeed manually in chrome and go to the “Optimize Images” area for the results…and then manually save the file that appeared after clicking “See Optimized Content” – it was very time consuming…
One question though…I run virtualmin and have several domains being hosting…they allow follow the schema of “/home/$username/public_html” for the home directory. I almost always work exclusively with WordPress and/or Opencart.
With that – WordPress images are located in “wp-content/uploads/year/month” and “wp-content/themes/themename/images”
Opencart images are in “image/data”
Based on this information, would it be possible to modify the script above (the one that replaces the old images with optimized images) and have it scan these directories (even if it scanned the whole “wp-content/themes/” directory, but NOT the “wp-content” directory)….and then optimize the images once they were found?
Is replacing the images dangerous? Is there a chance an image can be optimized and then the file gets broken?
I know I could run mod_pagespeed, and I have done that in the past. The fact is, I’m kind of anti-GXXGLE right now with the whole PRI$M / spy stuff…They are getting way to integrated into everything and it’s very unsettling….
I appreciate it!
First, backup all files. Next run the following to find every .png file in /var/www/html/wp/wp-content/uploads/ and run optipng on it. If something broken, you can restore it from backups:
find /var/www/html/wp/wp-content/uploads/ -iname "*.png" -print0 | xargs -I {} -0 optipng -o5 -quiet -keep -preserve -dir optimized -log optipng.log "{}"I’m getting this error
root@cp [~]# yum install optipng
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
* base: mirror.cogentco.com
* extras: mirror.trouble-free.net
* updates: mirror.rackspace.com
Setting up Install Process
No package optipng available.
Error: Nothing to do
Please help
Enable EPEL repo as described.