When saving images in a graphics or publishing program, users have three primary options for small, highly compatible images: JPEG (Joint Photographic Experts Group,) BMP (Bitmap) and PNG (Portable Network Graphics). Knowing when and where to use PNG images instead of JPEG or BMP is an important skill for graphic and Web designers, and can be a useful piece of knowledge for any professional working in a digital environment. Since the release of Windows Vista in 2006, PNG has been the standard format for high-quality Windows icons.
Portable Network Graphics
Portable Network Graphics, or PNG for short, is an image file standard developed in the mid 1990s. PNG was designed to replace the aging GIF standard, delivering better compression, quality and features. PNGs can achieve a much greater compression index than GIFs on large, complicated photos, while retaining the latter's ability to include transparency. PNG also has a much higher color depth, using 24-bit color instead of 8-bit. When large or high-quality images are being used in Web templates and other formats that require flexibility, PNG is an excellent alternative to GIF.
PNG vs JPEG
PNG and JPEG images have different applications. Generally speaking, JPEG images can be compressed to a much higher degree than PNG images, resulting in a considerably smaller file size. However, JPEG is a "lossy" standard, and at high compression rates, such as a quality rating of three or lower in Photoshop, image distortion becomes increasingly visible. JPEG does not use the same color system as PNG, and it is incapable of displaying transparencies. JPEG is a good choice for small, low-quality images, but when accuracy and quality are important, PNG is worth the extra file size.
PNG vs BMP
When compared to BMP (Bitmap) images, PNG excels in almost every area. BMP images are uncompressed, so file sizes will always be smaller in a comparable PNG image. PNG supports a greater color depth and transparency. Some Web developers and game designers still prefer BMP images, especially when programming for Windows, as the lack of compression means that smaller images will load faster. For almost every other application, PNG is the better choice.
Downsides to PNG Format
As a relatively new file format, PNG saw adoption issues in the early 2000s. While most modern browsers support all of the functions of PNG images, those developing with Internet Explorer 6 users in mind may want to choose something else, as it does not properly support PNG Alpha channels. As a rule of thumb, if you're creating graphics for hardware or software made before 2002, PNG should be avoided. Additionally, TIFF has largely eclipsed PNG for high-quality image applications in the photography and signage industries, due to its small size and high quality.