more information, see this article in the Microsoft Knowledge Base: 947864 MS08-024: Cumulative Security Update for Internet Explorer. 6.0 sometimes completely loses ability to display PNGs, but there are various fixes. 6.0 and below have broken alpha-channel transparency support (will display the default background color instead). 7.0 and below cannot combine 8-bit alpha transparency AND element opacity (CSS – filter: Alpha (opacity=xx)) without filling partially transparent sections with black. 8.0 and below have inconsistent/broken gamma support. 8.0 and below don't have color-correction support. Operating system support for PNG icons PNG icons have been supported in most distributions of Linux since at least 1999, in desktop environments such as GNOME. In 2006, Microsoft Windows support for PNG icons was introduced in Windows Vista. PNG icons are supported in AmigaOS 4, AROS, macOS, iOS and MorphOS as well. In addition, Android makes extensive use of PNGs. File size and optimization software PNG file size can vary significantly depending on how it is encoded and compressed; this is discussed and a number of tips are given in PNG: The Definitive Guide. Compared to GIF Compared to GIF files, a PNG file with the same information (256 colors, no ancillary chunks/metadata), compressed by an effective compressor is normally smaller than a GIF image. Depending on the file and the compressor, PNG may range from somewhat smaller (10%) to significantly smaller (50%) to somewhat larger (5%), but is rarely significantly larger for large images. This is attributed to the performance of PNG's DEFLATE compared to GIF's LZW, and because the added precompression layer of PNG's predictive filters take account of the 2-dimensional image structure to further compress files; as filtered data encodes differences between pixels, they will tend to cluster closer to 0, rather than being spread across all possible values, and thus be more easily compressed by DEFLATE. However, some versions of Adobe Photoshop, CorelDRAW and MS Paint provide poor PNG compression, creating the impression that GIF is more efficient. File size factors PNG files vary in size due to a number of factors: color depth Color depth can range from 1 to 64 bits per pixel. ancillary chunks PNG supports metadata—this may be useful for editing, but unnecessary for viewing, as on websites. interlacing As each pass of the Adam7 algorithm is separately filtered, this can increase file size. filter As a precompression stage, each line is filtered by a predictive filter, which