For websites and web development, the PNG image format is considered to be the best image format due to its small size, respective image quality and browser compatibility. However not all PNG formats are the same. The most preferred web-friendly format is called "8 bit PNG with alpha transparency" (explained here)

8-bit Alpha lets you convert a common 24-bit PNG image into an 8-bit image with alpha transparency. To convert, simply drag the 24-bit image from your computer onto the website, wait a little while and then download the converted 8-bit image to your computer. You can still do it in Photoshop, but if you don't have the software or if you don't want to wait while it loads, use this website instead.

8bitalpha

Features:

  • Convert 24-bit PNG images into 8-bit images with alpha transparency online.
  • Simply drag and drop to convert.
  • No registration or software to install.
  • Similar tools: AgileUploader, PunyPNG, Smushit and ImageOptimizer.

Check out 8-bit Alpha @ www.8bitalpha.com