Fireworks has four optimization features to help you find the right balance between file size and visual quality. The four features are the Export Wizard, optimizing in the workspace with the Optimize Panel or applying a Preset setting from the Property inspector, and optimizing in the Image Preview panel. This article will focus on the second and fourth optimization features.
Like GIF, PNG format enables you to specify the number of colors to use in optimization. The exported file size of a PNG will usually be less than that of a GIF for the same image. It may be less than that of a JPEG for the same image too. You’ll have to test it to know for sure. PNG can support up to 32-bit color and contain transparency or an alpha channel. It uses zlib compression and some extra filters to compress the image without losing any of the image data.