jon wrote: >> 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
That is useful to know - thank you. So in brief, it is recommended to save the original .jpg as a .png, then do all ones editing then save as a .jpg again for use in whatever_application. Would the quality of the original .jpg suffer visibly in a finished [Scribus] .pdf if I only cropped it (one edit and one save - ie. one generation) and re-saved (using the Gimp) at 100% ? Blessings, Nigel -- OliveRoot Ministries http://www.oliveroot.net/ PrayingForIsrael.net http://www.prayingforisrael.net/
