PNG Compression

PNG compression is able to considerable reduce the file size of an image without any loss of quality. While the jpg compression is quite lossy, in png compression there is neither a change of colours nor a reduction of colour depth. The number of colours exactly remains the same.

Ten steps of compression can be used for png images. Below is shown, how an image with maximum amount^[1] of possible colours is compressed from a file size of about 197kB, which is roughly the same as the corresponding bmp file size to 678 bytes, which is just 3.4‰ of the original size. Notice that already the first compression rate reduces file size to 1.8kB, i.e. 1% of its original size.

• image width : 256px
• image height : 256px
• number of pixel : 65,536
• number of colours: 65,536

PNG Compression Rates

Image with 65,536 colours Original image created by Paul Schmidt.	Rate	File Size [bytes]
Image with 65,536 colours	Rate	File Size [bytes]
	0	197,245
	1	1,795
	2	1,795
	3	1,809
	4	864
	5	860
	6	817
	7	817
	8	679
	9	678