test of PNG version - blond-long-haired-woman-surfmorrobay.com_0279
testing the lossless .png version of a photo - I thought Flickr only took JPGs, but I see at flickr.com/help/photos/?search=tiff#18 that now lossless PNGs can be uploaded to Pro accounts. HOWEVER, note that all EXIF data is lost - so it is hardly worth the effort to save one's images as PNGs - if the image is not to be further manipulated, it seems that a final save-as JPG in the highest quality level (12 in CS3 RAW converter) is the best compromise for saving images at Flickr. I wish I could save my .PSD file here.
Several formatted versions of this photo (.TIF .PNG .JPG) are in a test set www.flickr.com/photos/mikebaird/sets/72157602954969801/
This test PNG image is 6.81 MB vs 2.9MB for the highest-quality JPG version shown at www.flickr.com/photos/mikebaird/1849450523/ (for a factor of about 2X increased space).
PNG defined at en.wikipedia.org/wiki/Portable_Network_Graphics
Blond long-haired young lady woman watching the surfers at Morro Rock, Morro Bay, CA, Morro Strand State Beach taken from the parking lot, Sat. Nov. 03 2007 03nov2007 Photo by Mike Baird, Canon 1D Mark III w/ 600mm IS lens w/ 1.4X II tele-extender for 840mm, or tripod with gimbal head - bairdphotos.com flickr.bairdphotos.com photomorrobay.com surfmorrobay.com morro-bay.com
More info on using PNGs vs JPGs Vs TIFFs
en.wikipedia.org/wiki/Portable_Network_Graphics says in part (see link for full details):
JPEG can 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. 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.
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.