PNG Transparency: Win32 IE 7.0b1 Screenshots

PNG Transparency

Screenshots from Internet Explorer 7.0b1 for Win32

These are 40%-scale JPEG screenshots of the pngs-img.html, png-IceAlpha.html, png-MagnoliaAlpha.html, png-rgba32.html, and png-textures.html pages. They were taken by Michael Broschat using the first beta release of MS Internet Explorer 7.0 under Windows "Longhorn" Vista.

Click on the JPEG images to see the full-scale, 24-bit PNG versions (393243, 300959 and 629627 bytes, respectively):

pngs-img.html

png-IceAlpha.html

png-MagnoliaAlpha.html

There do not appear to be any errors in IE7's rendering of PNG transparency, whether full 32-bit RGBA, 8-bit RGBA-palette, or "cheap" single-shade transparency. As before, the images are linked to full-scale PNGs (1,111,681 and 391,410 bytes, respectively):

png-rgba32.html

png-textures.html

Note that what initially appeared to be a flaw in the full-scale version of the righthand image--specifically, the bright pixel near the center of the brain scan, image #15--turned out instead to be a simple scaling artifact. (The image is 128x128 natively, but it is displayed at 64x64 on the test page.)

IE7 does gamma correction (some of the time), but like its predecessors, it does not do so consistently. Nor does it do color correction at all, as these images show:

png-gammatest.html

png-colortest.html

The middle two rows of each block on the lefthand image show that while IE7 does gamma-correct PNGs with gAMA chunks, it does so with an assumed display-system exponent of 1.96 or 1.93. That would acceptable if and only if unlabelled GIFs and PNGs, PNGs with sRGB chunks, and HTML and CSS colors were gamma-corrected in the same way. They are not, however; only PNGs with gAMA chunks are adjusted, and this is incorrect behavior for a browser.

Both the second row on the color-test page and the final row in each block of the gamma-test page demonstrate that IE7 ignores the PNG ICC profile chunk (iCCP). It also ignores the PNG chromaticity chunk (cHRM, first row on color page). This is allowed behavior, according to the PNG spec...but insofar as Microsoft was one of the founding members of the International Color Consortium--or the "InterColor Consortium," as it was known in 1994, before the PNG format even existed--it would have been nice to see a little more support for color correction. (On the other hand, this was tested with beta versions of both Internet Explorer and Windows Vista, so the final release may be a different story.)

Here are some related PNG pages at this site:

Last modified 14 March 2009.