Navigator/PNG bKGD Test

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)

Last modified 14 March 2009.