I am no expert in graphics or images but I do have some basic knowledge about them such as GIF is normally used for animated images, JPEG is for high quality pictures, BITMAP, I have no idea what is it for because the file size is huge, and finally PNG, the image format that I normally use in this site because the size is small and the quality is pretty good as well. If you do a search on JPG vs GIF vs PNG, you’ll find a lot of information about these image formats and each has its own pros and cons.

Another thing I know is images can be compressed into smaller size. Reason is I get to save my webhost bandwidth and also you guys can load up the page faster. I normally use HyperSnap-DX to capture screenshot and also to do simple image editing. It can save the screenshot in many different image formats and lets you to choose if you want a higher quality or smaller size when I want to save the image. The images saved by HyperSnap is pretty small but I never knew that it could be compressed further. Compressing images and making it smaller is important as long as the quality of the image is not affected. Here are 4 free small and portable tools that can compress PNG images.

I’ve put all 4 PNG compressors to the test to see how much time it requires for maximum compression and also the size of the PNG file that it managed to reduce.

1. OptiPNG
OptiPNG compress PNG
OptiPNG 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. It is a command line utility, so you’ll need to read the manual on the command line switches. The command line for OptiPNG to compress at maximum is “optipng -o7 image.png”. Take note that it is the letter o and NOT number zero. There is a a GUI for OptiPNG called akJ OptipngWrapper created by Aki which runs on Java.

OptiPNG took 48 seconds to compress a 170050 bytes PNG image file to 166204 bytes (-2.26%).

2. pngcrush
Pngcrush is an optimizer for PNG (Portable Network Graphics) files. It can be run from a commandline in an MSDOS window, or from a UNIX or LINUX commandline. Its main purpose is to reduce the size of the PNG IDAT datastream by trying various compression levels an PNG filter methods. It also can be used to remove unwanted ancillary chunks, or to add certain chunks including gAMA, tRNS, iCCP, and textual chunks. Also a command line utility and there are many switches available. The maximum compression command is “pngcrush -brute image.png”.

pngcrush took 30 seconds to compress a 170050 bytes PNG image file to 167059 bytes (-1.75%).

3. AdvanceCOMP
AdvanceCOMP is a collection of recompression utilities for .ZIP archives, .PNG snapshots, .MNG video clips and .GZ files. It recompress ZIP, GZ, PNG and MNG files using the Deflate 7-Zip implementation. Also a command line utility. The command for highest compression for PNG file is “advpng -z4 image.png”.

AdvancedCOMP took 11 seconds to compress a 170050 bytes PNG image file to 163840 bytes (-3.65%).

4. PNGOUT
PNGOUT optimizes the size of .PNG files losslessly. It uses the same deflate compressor that the author wrote for KZIP.EXE. With the right options, it can often beat other programs by 5-10%. That includes pngcrush -brute, optipng -o7, advpng -z4, etc. The command line for highest compresson for PNG file using PNGOUT is “pngout image.png”. By default it uses the Xtreme compression which is the highest.

PNGOUT took 141 seconds to compress a 170050 bytes PNG image file to 152409 bytes (-10.37%).

As you can see, PNGOUT did manage to beat the rest of the PNG compressors like it said but it sure took a lot of time to do it. AdvancedCOMP did pretty well because it took only 11 seconds to complete the process and it has higher compression than OptiPNG and pngcrush.

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