Kraken is a free online image optimizer that supports both lossless and lossy optimization mode. You can also either choose the source of image from your computer or paste a list of URLs. The PNG image file is then being “kraked” and uploaded to their CDN for 1 hour temporary storage. The good thing about Kraken.io is they have Chrome and Firefox extension with a limited free API usage. Paid plans for advanced API usage will be released in a few weeks. According to our test, Kraken’s free compression is comparable with the paid PunyPNG’s extreme compression.
pngoptimizer.com is a very simple website that allows you to upload images up to 3MB for compression. Just click the browse button to look for the image file and followed by clicking the Optimize button which is very close to the advertisement block. From the test results, we were able to determine that pngoptimizer.com is using OptiPNG to compress PNG files.
PunyPNG has gotten a lot of attention after a side-by-side comparison of PunyPNG shaving off more bytes than its competitors being posted online. They offer a free compression and if you sign up for a PRO plan, you automatically get the Extreme and Lossy compression. To compress PNG images, click the Upload Images button and you can select up to 15 files with a maximum of 150KB each as a free user. A PRO account gets 50 files with 500KB each.
Smush.it is the most used online optimization tool hosted in the Yahoo Developer network and the functionality is included in YSlow. You can find nearly every application that support Smush.it, for example a WordPress plugin that allows you to easily and even automatically “smush” the images upon uploading to your server. There are 2 methods to compress your images at Smush.it which is either by uploading the files from your computer or specify the URL linking to the images.
TinyPNG only does lossy compression where there will be a slight degrade in quality that can’t be seen by the naked eye to achieve a much smaller file size. So if you have a 24-bit PNG image, compressing it in TinyPNG will become an 8-bit PNG file. It supports 20 images at a time with a generous 3MB each.
PNG Compression Test
Compression results for two 8-bit PNG files
Compression results for two 24-bit PNG files
Summary: ScriptPNG is able to produce the smallest compressed file size for both 24-bit and 8-bit PNG files. Take note that ScriptPNG is merely a script that uses a collection of compression tools to further optimize the PNG file and it takes much longer to process than other command line alternatives. Take note that although PNGOUT compresses really well on 8-bit PNG files, it is the worst performing PNG compressor for 24-bit PNG files.
Although unmentioned, we believe the online PNGoptimizer.com service is using OptiPNG on their server to compress PNG files because they produce the exact same size on all 4 tests. Our tests also shows that Kraken Image Optimizer is able to produce the same results as PunyPNG Extreme compression available only to their paid users.
Additional Tip for Command Line Users: If you need to frequently use the command line tools but hate to retype the full command each time you want to optimize and compress PNG files, here is an easy solution that turns typing commands into two mouse clicks. What you can do is add a new action to your context menu that only appears when you right click on PNG files but not on others.
1. Download ExtMan, extract and run the portable executable file.
2. By default the language of the program interface is shown in German, simply click on the US flag icon on the window to switch to English.
3. Scroll down the list and look for the “png” extension with the filetype shown as “PNG Image”.
4. Double click on png extension and click the New action button.
5. You can enter anything on the Process box, preferably either the name of the PNG compressor or simply just Compress if you intend to use only one command line tool.
6. As for the “Applications for this Process” box, you will need to enter the following command line depending on the command line tool that you’re using. Please change the path of the tool if you’re not going to put it in the root of your C:\ drive.
- advpng: C:\advpng.exe -z4 "%1" (Overwrite existing PNG file)
- OptiPNG: C:\optipng.exe -o7 -backup "%1" (Creates a backup of existing file by adding .bak extension)
- Pngcrush: C:\Pngcrush.exe -brute -e _compressed "%1" (Saves the compressed PNG file as original filename + _compressed.png)
- PngOptimizerCL: C:\PngOptimizerCL.exe -BackupOldPngFiles -file:"%1" (Backup original PNG file by adding an underscore character at the beginning of the filename)
- PNGOUT: C:\pngout.exe "%1" out.png (Saves compressed PNG file as out.png)
- ScriptPNG: C:\scriptpng\ScriptPNG.cmd "%1" (Press number 9 and overwrites existing PNG file)
- TruePNG: C:\TruePNG.exe "%1" /o max /out out.png (Saves compressed PNG file as out.png)
7. Click the Save button to close the Action window and again click the Save button to close the Edit window.
8. Whenever you right click on a PNG file, you will have an extra command at the context menu to compress the file.