This is a test image that demonstrates a bug in Netscape Navigator versions 4.04 through 4.75 (but not in any version of Mozilla, apparently): a palette PNG with a background-color chunk (orange: 255,127,0) but no transparency and no use of the background color in the main image data is nevertheless rendered as though black (0,0,0) is transparent.
Here's what the image should look like:
Here is the pngcheck -v output of the ``bad'' version:
File: pngnow-test2.png (2190 bytes)
chunk IHDR at offset 0x0000c, length 13
98 x 31 image, 8-bit colormap, non-interlaced
chunk PLTE at offset 0x00025, length 768: 256 palette entries
chunk bKGD at offset 0x00331, length 1: index = 255
chunk tEXt at offset 0x0033e, length 53, keyword: Comment
chunk IDAT at offset 0x0037f, length 1275
zlib: deflated, 32K window, default compression
chunk IEND at offset 0x00886, length 0
No errors detected in pngnow-test2.png (27.9% compression).
No tRNS chunk, no alpha channel...ergo, no transparency. The IDAT data are identical to the original pngnow.png image displayed above (and also visible on the PNG home page).
(Discovered by Glenn Randers-Pehrson, 3 September 1998)
Copyright © 1998-2009 Greg Roelofs.