In a mixed platform world of Macintosh, Windows, and Unix computers, you must pay attention to how you name your file. On PCs, you usually append a three-letter file extension after the file name to tell the computer what program to launch when it is double-clicked. Programs on the PC do this automatically, but the same programs running on the Mac often do not. However by default Photoshop 5.5 appends the proper file extension to various file formats, i.e. JPG, TIF, PSD, etc. Even still, there are things you should avoid when naming files for use on all platforms (i.e., web images, multi-media/CD presentations).
Things to avoid:
Don't add extraneous punctuation to the file name. For example, don't use #. %, forward or back slashes, ampersands, and question marks or any other strange glyph. Stick mostly to letters and numbers. Dashes and underscores are OK.
Good: my_file.jpg
Bad: my/file.jpg
Don't put more than one period in the file name. Use only one period at the end of the file name just before the three-letter suffix.
Good: very_big_splash.jpg
Bad: very.big.splash.jpgDon't omit the 3-letter suffix. Add the correct 3-letter suffix to the file name if none is created by the application program. ALL web browsers require a suffix to be able to tell a picture file from a text file, for example. Don't add inaccurate suffixes either. If you name a TIF file "goodpicture.jpg", the picture won't display properly on a web browser. For a list of PC file name suffixes, go to suffix.htm.
Good: promopic.gif
Bad: promopic.newone
Bad: promopicAvoid spaces in filenames. High-speed Unix-based web servers dislike having spaces in the file name. Your pages and files with spaces in the name may work on a Mac or PC server, but if you ever migrate the files to a Unix server, you're in trouble. Most experienced web designers use underscores in the file name to separate words for clarity.
Good: my_new_car.jpg
Bad: my new car.jpg
Opening PC files on a Mac:
Opening a PC-created picture file (like a jpg) on the Mac confuses beginning users. They double click the icon, and some other program on the Mac opens the file for viewing - usually Apple QuickTime. It is not loaded into Photoshop like they expected.
Macintoshes use a hidden bit of information called the Resource Fork to tell the computer what program to launch when the file icon is double-clicked. Each program that creates a file writes this information when you save. When you copy a PC file onto the Mac, the resource fork is missing. In order to open a file from a PC, you usually have to open the program first (i.e. Photoshop), then do a File, Open from within the program. Once the file is re-saved, the missing resource fork is added, and the file becomes a Mac version.