First, "file format" refers to how an image file is saved, and is determined by how the image is to be used. In Photoshop, when you choose "File / Save" (or "Save As" or "Save a Copy") you will see the menu below.
The end use of a file will determine the best file format choice. If you don't know what your end product will be, stick with the native Photoshop (.psd) format, then "Save As" when you figure it out. The annotated charts below discuss the most commonly used Photoshop file formats.
Common File Formats for Graphic Applications
| File Format | File Extension | Notes |
| Photoshop | .psd | The native Photoshop format -- supports Photoshop's layers and transparency. Good option for the CS workflow. |
| Photoshop EPS | .eps | Encapsulated Postscript File -- supported by Adobe CS but not necessarily by all other graphics applications. Supports Paths, but not transparency. |
| Portable Document Format -- a versatile cross-platform format. | ||
| TIFF | .tif | Tagged-Image File Format -- a cross-platform format that supports lossless compression (no image data is discarded as it is saved; see JPG below). Supports transparency, but not Paths. |
| Note: Photoshop, EPS, TIFF and PDF formats are supported by all Adobe Creative Suite applications. | ||
Common File Formats Used on the Web
| File Format | File Extension | Notes |
| GIF | .gif | Prounounced "jif" or "gif," it stands for Graphics Interchange Format. Good choice for line art or art with limited palettes, animation; supports transparent backgrounds. |
| JPG or JPEG | .jpg | Joint Photographic Group Experts File -- a good option for displaying or sharing images on the web or via email, but degrades image through "lossy" compression. Image data is discarded in order to compress file size, that is, to make the file size smaller. Each time a file is saved in jpg format it continually degrades the image. |
| PNG | .png | Portable Network Graphic. It was developed an alternative to the GIF format and supports lossless data compression and transparent backgrounds. Does not support CMYK colorspace. |
| Note: Choose "File / Save for Web" when saving images for use on the Internet. For more details, see Photoshop's Help menu. | ||
Other File Formats
| File Format | File Extension | Notes |
| Bitmap | .bmp | Windows-compatible format; lossless (loses no data when saving, unlike lossy formats such as JPG). |
| PCX | .pcx | A Windows file format. |
| PICT | .pct | A Macintosh format. |
| Pixar | .pxr | For use with high-end 3-D imaging programs. |
| PNG | .png | An alternative to GIF format. See above. |
| Raw | .raw | Saves files as a stream of bytes, good only for moving between applications and platforms. |
| Scitex | .sci | For high-end graphics, such as super-high resolution drum scans. |
| Targa | .tga | For systems using Truevision® video board. |
— Adapted and updated from: Teach Yourself Photohop 4 in 14 Days. D. Bront Davis, Steven Mulder, Carla Rose, Hayden Books, 1997.
Further reading
http://livedocs.adobe.com/en_US/Photoshop/10.0/help.html?content=WSfd1234e1c4b69f30ea53e41001031ab64-7784.html
http://www.creativepro.com/article/graphics-fundamentals-understanding-photoshop-file-formats-
http://ezinearticles.com/?Photoshop-Files-and-Formats&id=36741
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