About Portable Network Graphics (.png) format
Portable Network Graphics (.png) is a graphic file format supported by many Web browsers. It is a good format for compressing and storing graphic images, and there is no loss of graphic image data when an image is uncompressed. The .png format supports variable transparency of images (alpha channels) and control of image brightness on different computers (gamma correction). It is used for a wide range of graphics from small images (such as bullets and banners) to complex images (such as photographs).