> Does this mean (with regards to the image quality) that it is > better to save > photos as .png's since it is a lossless format? Do .png's have a > better or similar > image quality as un-altered .jpg's? > This is from wikipedia: JPEG will produce a smaller file than PNG for photographic (and photo- like) images since it uses a lossy encoding method specifically designed for photographic image data. Using PNG instead of a high- quality JPEG for such images would result in a large increase in filesize (often 5?10 times) with negligible gain in quality.
PNG is a better choice than JPEG for storing images that contain text, line art, or other images with sharp transitions that do not transform well into the frequency domain. Where an image contains both sharp transitions and photographic parts a choice must be made between the large but sharp PNG and a small JPEG with artifacts around sharp transitions. JPEG is a poor choice for storing images that require further editing as it suffers from generation loss, whereas lossless formats do not. This makes PNG useful for saving temporary photographs that require successive editing. When the photograph is ready to be distributed, it can then be saved as a JPEG, and this limits the information loss to just one generation. That said, PNG does not support Exif image data from sources such as digital cameras, which makes it problematic for use amongst amateur and especially professional photographers. TIFF does support it as a lossless format, but is much larger in file size for an equivalent image. JPEG has historically been the format of choice for exporting images containing gradients, as it could handle the color depth much better than the GIF format. However, any compression by the JPEG would cause the gradient to become blurry, but a 24-bit PNG export of a gradient image often comes out identical to the source vector image, and at a small file size. As such, the PNG format is the optimal choice for exporting small, repeating gradients for web usage. Comparison with TIFF TIFF is a complicated format that incorporates an extremely wide range of options. While this makes TIFF useful as a generic format for interchange between professional image editing applications, supporting specific applications such as Web browsers is difficult. It also means that many applications can read only a subset of TIFF types, creating more potential user confusion. The most common general-purpose, lossless compression algorithm used with TIFF is LZW, which is inferior to PNG and, until expiration in 2003, suffered from the same patent issues that GIF did. There is a TIFF variant that uses the same compression algorithm as PNG uses, but it is not supported by many proprietary programs. TIFF also offers special-purpose lossless compression algorithms like CCITT Group IV, which can compress bilevel images (e.g., faxes or black-and- white text) better than PNG's compression algorithm. ---- Jon
