Some questions to consider: is the format suitable for print or the Web? Is it compatible with other graphics programs or platforms (essential if you are sharing files). Is the format lossy, i.e., will I lose information each time I save the file? For more information about some of the limitations of types, see the July 2000 Graphics column. Also, does your graphics program support the file formats you want to use?
The first limitation you will face is that while many free programs can open a range of file formats, not all can convert them to other types (the Wang Imaging program that shipped with Windows 95 is a good example). If you want to practise converting files across a range of formats, try the Paint Shop Pro trial version and free IrfanView on the cover CD. Before buying a program, you should be careful to check that your graphics program can support the file types you want to use. Special note: if you are going to practise on the trial version of Photoshop then you are in for a shock - it doesn't allow you to save files. So it is useless for this task.
Regardless of which program you prefer, the steps for converting graphics are generally the same.
Start the graphics program, and:
Open the existing file you wish to convert (generally File-Open)Select 'Save As' from the file menu (generally File-Save As)A dialogue box should appear - one of the options should be "Save As" file type. This is where you chose the format you wish to convert the file into. Hit Save and you should be done.
Most advanced programs allow users to tweak certain options. Graphics formats can have a myriad of choices but most allow a user to balance between file size and quality. In Paint Shop Pro and IrfanView, when you select Save As, the dialogue box that appears will have a button called "Options".
Here you can adjust the settings of a file type, or you can ignore it and use the default values (beware, it will also preserve your last settings and apply them until you alter them again). Photoshop is a little counter-intuitive in its approach, in that a dialogue box to adjust the compression options will appear after you hit the Save button.
A common problem is that sometimes, when you hit Save As, you will find that there is only one file type that the program will let you select (on occasion there may even be a few listed). This is due to some formatting in your picture that is not supported by any format other than the one used by the program. The most frequent cause is layers. For example, if you haven't merged or flattened an image that has layers, then Photoshop will not let you save it as a JPEG - only PSD will be available.
Some programs have an Export feature but this function varies so widely across programs and even between version numbers that it will have to be covered another time (alternatively, consult the program's Help file).
So, lets say that you have a file and you want to convert it to a JPEG. Open the file in the graphics program. Select Save As. A box will appear and from the file type list, select JPEG. In Paint Shop Pro you can adjust the JPEG quality by clicking on Options. A compression factor of 70 should be set for Web sites and 30 or higher for print. Photoshop will display a similar box but you have to select Save and then it will appear. Adjust its Quality setting to about 3 for the Web and at least 7 for print.
When converting files to TIFF format you can easily fall into a common trap: there are many types of TIFF formats and not all graphics programs support all the different flavours. You may save a file with LZW compression called party.tif, but if you send it to someone else and their program doesn't support that type of TIFF, it will not open. Furthermore, there is no easy way to identify what type of TIFF they have used. Try to avoid TIFF until you have experimented more with its peculiarities. The options box in Paint Shop and IrfanView list a few of the common varieties.