alpha. Software support The official reference implementation of the PNG format is the programming library libpng. It is published as free software under the terms of a permissive free software license. Therefore, it is usually found as an important system library in free operating systems. Bitmap graphics editor support for PNG The PNG format is widely supported by graphics programs, including Adobe Photoshop, Corel's Photo-Paint and Paint Shop Pro, the GIMP, GraphicConverter, Helicon Filter, ImageMagick, Inkscape, IrfanView, Pixel image editor, Paint.NET and Xara Photo & Graphic Designer and many others. Some programs bundled with popular operating systems which support PNG include Microsoft's Paint and Apple's Photos/iPhoto and Preview, with the GIMP also often being bundled with popular Linux distributions. Adobe Fireworks (formerly by Macromedia) uses PNG as its native file format, allowing other image editors and preview utilities to view the flattened image. However, Fireworks by default also stores metadata for layers, animation, vector data, text and effects. Such files should not be distributed directly. Fireworks can instead export the image as an optimized PNG without the extra metadata for use on web pages, etc. Web browser support for PNG PNG support first appeared in 1997, in Internet Explorer 4.0b1 (32-bit only for NT), and in Netscape 4.04. Despite calls by the Free Software Foundation and the World Wide Web Consortium (W3C), tools such as gif2png, and campaigns such as Burn All GIFs, PNG adoption on websites was fairly slow due to late and buggy support in Internet Explorer, particularly regarding transparency. PNG compatible browsers include: Apple Safari, Google Chrome, Mozilla Firefox, Opera, Camino, Internet Explorer 7 (still numerous issues), Internet Explorer 8 (still some issues), Internet Explorer 9 and many others. For the complete comparison, see Comparison of web browsers (Image format support). Especially versions of Internet Explorer (Windows) below 9.0 (released 2011) have numerous problems which prevent it from correctly rendering PNG images. 4.0 crashes on large PNG chunks. 4.0 does not include the functionality to view .png files, but there is a registry fix. 5.0 and 5.01 have broken OBJECT support. 5.01 prints palette images with black (or dark gray) backgrounds under Windows 98, sometimes with radically altered colors. 6.0 fails to display PNG images of 4097 or 4098 bytes in size. 6.0 cannot open a PNG file that contains one or more zero-length IDAT chunks. This issue was first fixed in security update 947864 (MS08-024). For