PNGQuant is by far the best free PNG optimization software on the net. This software uses lossy compression and converts PNG images into an optimized 256 color PNG-8 format. The resultant images can be reduced to more than 70% of their original size with minimal loss in quality. It goes without saying that optimized images load relatively faster saving you bandwidth and improving user experience. Let's see how you can use PNGQuant to compress your PNG images for the web in this short tutorial.
PNGQuant is a command line application and if you are not familiar with command line a simple alternative is to use PNGoo which is a GUI application for windows or PNGYu for Mac users. In addition to these, the software also has a plugin for photoshop uses known as SuperPNG.
In this article, I will be discussing PGNoo for windows users. To start off, you can download PNGoo by visiting pngquant.org website and then clicking on PNGoo link under the GUI section. Once downloaded, unzip the file and you should be able to see a folder named 'libs' and an application file named 'PNGoo'. Double click on this application file to open the software.
Using PNGQuant (PNGoo)
Here are the steps on how you can use PNGoo to compress your images.
Step 1: Click on Add Files and select PNG images that need to compress. You can select as many images as you want.
Step 2: If you want to overwrite your original PNG images, then click on the 'Output to Same Directory (Overwrite PNGs)' Option. If not, click on 'Browse' and select a directory where you would like the optimized/compressed images to be saved in. (refer image below)
Step 3: At this point, you can click on the Go button and all your images will be optimized to a 256 color palette. But in-case you want even further compression, click on 'Color Settings' under 'Compression Options' and experiment using lower color settings for your images. (refer image below)
Getting Even More Compression
A simple way to compress your images even further is to optimize your lossy compressed images using a lossless compression software. This can compress your PNG images by an additional 5% to 10% without any additional loss in quality. One of the best lossless compression software which I personally recommend is PNGOutwin. This software a paid software and comes with a one month free trial. The cost for a single user thereafter is $14.
The free open source version of this software is PNGOUT but it is a command line application. If you would like to try that out, here is a tutorial on using PNGOUT using command line. Some other free alternatives for lossless compression are PNGCrush and OptiPNG. But again, both these are command line applications and there is no GUI alternative (for windows) available for these as of now.
One other alternative, is to use Compressor.io which is a free online service offering both lossy and lossless compression for PNG images. Lossy compression is done using PNGQuant and Lossless compression using OptiPNG. To losslessly compress your images, go to Compressor.io and select 'lossless' under the 'Choose Your Compression' option before uploading your file. The drawback to this is that you will need to upload your images one by one as there is no bulk uploading options available.