This set is provided courtesy of Stefan Schneider. If the two images on the right are transparent but the one on the left has a black background, the browser was probably compiled with a buggy version of libpng. The bug is fixed in libpng 0.96 and later, and a trivial patch is available (for browser implementors, that is) for earlier versions of libpng.
The image on the right is a full 32-bit RGBA image (that is, truecolor with a full alpha channel). The two on the left are 8-bit palette images with full transparency chunks--in other words, their palettes are effectively RGBA values instead of the normal RGB. The one on the left has a 256-entry palette, while the one in the center has 255 entries; both were created with Stefan's LatinByrd application.
As a nice demonstration of the power of the palette-alpha images, here's a composite JPEG image of the toucan on top of his twin, provided by Glenn Randers-Pehrson. Note how the shadow of the toucan in front falls across his buddy:
The following set is provided by Greg's colleague, Pieter van der Meulen. All of these images are interlaced, have transparency, and should be rendered with the same green background as the page. If the images have obvious rectangular borders (due to the color specified in the bKGD chunk), the browser is broken. (The images should use their respective bKGD colors when viewed in a stand-alone image viewer with no default background of its own, however.)
These images are quarter-scale, interlaced, RGBA-palette (8-bit) versions of the original 32-bit RGBA images; each is between 35k and 70k. Click on any of them to bring up a page with the corresponding half-scale version of the image (also 8-bit), which in turn is linked to the full-size, 32-bit version. The conversion to 8-bit palette mode was accomplished by means of modified versions of some of the NetPBM tools.
[gratuitous link to Willem's test page with a large, interlaced image]
Here are some related PNG pages at this site:
Copyright © 1997-2009 Greg Roelofs.