What does the PNG format preserve when saving images?

The PNG format is well-known for its ability to preserve transparency in images. This feature sets it apart from many other image formats, making it a preferred choice for graphics that require transparent backgrounds, such as logos or web images. When saving an image in PNG format, the transparency information is retained, allowing the image to blend seamlessly with different backgrounds rather than displaying a solid rectangle around the image.

In terms of the other options, file size varies depending on the image complexity and color palette; image quality is typically high but can be subjective depending on the compression method; and color depth is supported to a significant extent in PNG, allowing for a range of colors, but is not the primary defining characteristic of the format. The presence of transparency is a unique and fundamental feature of PNG that directly contributes to its use in various applications.