> From: Lodge, Phillips Sent: Wednesday, November 17, 2004 6:35 > > Sorry for being thick, but... > > I have been following Shangara's and other's experiments and have > become thoroughly confused. > > I thought that modification of metadata by programs like ThumbsPlus or > PhotoMechanic or a host of others including PS was a lossless process > if you did not actually open the graphic. I have been playing around > with PhotoMechanic and it modifies files jpegs far too quickly for > them to have been opened and recompressed. (Except for when it fails > to modify them at all, when it should).
As I tried to mention earlier, it is important to differentiate what is really happening inside the computer. That a file is "opened" does not mean that the data is lost or damaged, that depends on how the program is written. First, there is the compressed data on the harddrive; this is then read into the RAM. From that data, the program calculates and creates an uncompressed display image. The program might or might not erase the compressed copy in RAM at that point but never the original on the hard drive. After changes are made to the EXIF and the program is told to save the file there are several options: 1. Read the compressed data again from the hard drive, add the changed EXIF data and save it back to the hard drive: No lost data. 2. If the compressed data copy is still in RAM, save it back to the hard drive with the new EXIF: Again, no data loss. 3. The not so smart program will use the uncompressed display image and compress it again and then save to the hard drive: Data loss. The tests that many person are running are very helpful to figure out what a program is doing but the manufactures of the programs ought to state clearly when there is recompression of data and when it is untouched. Bertho =============================================================== GO TO http://www.prodig.org for ~ GUIDELINES ~ un/SUBSCRIBING ~ ITEMS for SALE
