If you want to insure the most flexibility in your images, make sure to save your images in the Photoshop Document (PSD) format. The PSD format is the only format that supports all of the features found in Photoshop itself.
You can specify the default format in which to save files in the File Handling preferences dialog box.
1. If you are a Macintosh user, go to the Photoshop menu and select Preferences -> File Handling. If you are working in Windows, choose Edit -> Preferences and select File Handling.
2. To insure greater backwards compatibility for your files with older versions of Photoshop, check Always Maximize Compatibility for Photoshop (PSD) Files.
3. If you work on or save an image using an earlier version of Photoshop, unsupported features are discarded.
4. If you familiarize yourself with the new features in this version of Photoshop, you can gauge to what extent your PSD file is backward compatible with earlier versions of the software.
New features unique to Photoshop CS are Hard Mix blend mode, new adjustment layers, Layer Comps, placing text on a path, Photo Filter, Shadow/Highlight Correction, video format pixel aspect rations, color replacement brush tool, and filter gallery.
5. Likewise, if you are familiar with the features of past versions of Photoshop, you can anticipate your digital imaging needs more easily. Features unique to Photoshop 7 are the Linear Burn, Linear Dodge, Vivid Light, Linear Light, and Pin Light blending modes and the Layer Mask Hides Effect and Vector Mask Hides Effect advanced blending options.
Features unique to Photoshop 6.0 are layer sets, layer color-coding, layer clipping paths, fill layers, layer styles, editable type, and advanced type formatting. Photoshop 6.0 also added new layer effects. Photoshop 5.0 also introduced layer effects; however, effects added in later versions of Photoshop are not supported.
Photoshop 5.0 added color samplers, spot channels, and embedded ICC profiles. And Photoshop 4.0 featured adjustment layers and guides.
6. To save a file in the Photoshop file format, click Save and choose Photoshop from the Format drop-down menu.
7. Select the location where you want to save the file. 8. Select the options you want, and press OK.