The lack of good transparency support of PNG images
The PNG image format has some features typical of JPEG and GIF files. JPEG is good for displaying photographic images with non-contiguous colors. GIF is more appropriate for displaying 256-color line art. PNG is appropriate for both image types and supports alpha channel. If the image contains alpha channel, you can create dramatic effect by adjusting the image transparency. Still, IE versions older than IE 7 do not support PNG transparency. If you browse to a web page that contains an image that has a transparent background in Portable Network Graphics (PNG) format, the image background may appear to be gray rather than transparent. Converting PNG to GIF
is a way to solve the problem. Although PNG was developed to replace GIF, they have a lot in common, and in some ways GIF even surpasses PNG due to the ability to support animation. It's very suitable for the web and can compete with JPEG in this respect, especially when dealing with line art and images with few colors. ImageConverter Plus provides overall support for the GIF image format. The software supports the multipage layout of GIF, controls the number of colors and quantization. Please note though that GIF transparency is different from PNG: each pixel will either become fully transparent, or a solid color. In GIF, transparency is effective just for a specific color you will choose for a pixel.