Pages of Examples


Each page contains nine images together within statistics about them. The images are: PNG encoding of the original, six PNG encodings following pack4png with anti-aliasing and three PNG encodings following pack4png without anti-aliasing. The caption under (or next to) each processed image lists the compression strategy, the space in bytes of the PNG file, the percent of its size with respect to the original PNG file, the number of zones per basic color, and the root mean square error between the original and the packed image. It has been known for over 30 years that this is not a good measure of image quality but many people are not aware of that fact and its inclusion here is meant to illustrate that limitation (see discusssion in Section 6.4 of the paper).

Color Images

"Winter Sale" This is an image that has been scanned from a sales catalogue and besides the normal blurring by the scanner there are traces from the back page. Because the original was supposed to have only two colors pack4png works very well here achieving 25:1 additional compression for a total of 57:1 with no visible loss in quality. (The compression is not as good as in pack4png version 1.0 where additional compression was 28:1 but the current implementation is more robust overall.) See Section 6.3 of the paper for comparisons with JPEG for this and the other images in the set.

Part of IAPR logo This is a three color image (orange, gray, and white) that has been blurred by JPEG encoding. The original was JPEG so pack4png eliminates artifacts introduce by that method. Additional compression of 18:1 is achieved compared to 10:1 for version 1.0. (For compression with anti-aliasing pack4png version 1.0 kept the shadow cast by the letters in the original logo but it introduced color distortions in it.)

Dilbert gets less than a raise and Dilbert with M.T.Suit These images contain several colors including halftones but pack4png still helps by providing about 4:1 additional compression with no significant drop in quality.

Dartmoor Landscape This has been used by Ed Avis for his work on lossy PNG compression and it is has been obtained from The image has a large range of colors and it does not fit the pack4png model, therefore additional compression is only 1.5:1 before asignificant drop in quality occurs.

Gray Images

Serenading Mouse This is part  of a scanned New Yorker cartoon. Highest additional compression is about 10:1. (Not as good as in version 1.0 where it was nearly 20:1.) There is also a page showing GIF encodings.

Gray version of "Winter Sale" Parts of this image were used in Figure 3 of the paper.

Gray version of Dilbert with M.T.Suit Additional compression here is 4:1 for good quality approximations.

Paper discussing the method