If you save as a .gif, the picture mode must be changed to indexed color, which allows only 8 (maximum) color representation. You are thus discarding an IMMENSE amount of image information with this change, if the original was a high-color-depth RGB (or CMYK) image. Most "consumer grade" programs actually convert to 4-color indexing if no choice is offered.

While it is possible for a .gif file to specify specific colors for the index, most "consumer grade" programs use defaults, which may not be the same as the defaults for the program (or printer) that later interprets the file.

The .gif format will not lose additional resolution if the same file is saved repeatedly from the same program, but changing to .gif the first time is horribly destructive if the original file contains good (esp. color) information. The discarded information is not retrieved by changing back to another format.

If you open a .jpg in an editing program, and save from the program without making any changes to it, there can be significant loss of detail when the file is re-compressed repeatedly, if you are using significant amounts of compression. If you made no changes, there is no reason to save repeatedly, since the same file is already saved. Just don't save if you don't need to.

If you open and save a .gif without changes the file is (theoretically) compressed by the same (theoretically) lossless method so it should be unchanged; but again, this is a rather useless exercise if you're not doing anything to the file before you re-save it.

In any case, if you make any changes to the image by re-sizing, changing pixel density, etc, you lose some resolution. There's nothing magic about any of the available formats that can prevent the simple fact that any change is a blur filter. You just have less information to start with using a .gif, so you get less information at the end.

The loss when .jpg files are repeatedly worked and saved is relatively small if low compression values are used. Some programs allow "zero compression" in which there is NO LOSS, but of course an uncompressed .jpg is at least as large as the bitmap, and may in fact be significantly larger. Programs that don't allow you to choose how much to compress when saving .jpg files should be avoided or used very carefully.

In most of the better programs, a "native format" is used for processing, regardless of the original file format; and saving in that format gives zero "saving loss." Some programs do this by simply not compressing and others use true lossless compression. Unfortunately there, the native format can only be viewed by others who have the same program.

The ONLY commonly "sharable" format that can be created without discarding information and can be saved without discarding additional information is a .bmp. Several formats can do one or the other, but only the .bmp does both and is readable by nearly all programs.

Opening a file and saving it under a new name is unlikely to "fix" anything. If the file contains "errors" the "errors" will be loaded and saved with the new name. Saving in any different format requires reconstructing the file in the new format, and the "errors" may (or of course may not) be discarded. Reloading the new file in its new format and converting back to the the original format offers some hope that the file will be "reconstructed" into the original format and will not include the original error. If you don't change the format, you might as well just change the filename in Win Explorer.

You would of course want to chose a format for the "intermediate file" that doesn't produce a lot of image degradation in the conversion process.

John