Photoshop files have default file extension as .PSD, which stands for “Photoshop Document.” A PSD file stores an image with support for most imaging options available in Photoshop. These include layers with masks, color spaces, ICC profiles, CMYK Mode (used for commercial printing), transparency, text, alpha channels and spot colors, clipping paths, and duotone settings. This is in contrast to many other file formats (e.g. .JPG or .GIF) that restrict content to provide streamlined, predictable functionality. A PSD file has a maximum height and width of 30,000 pixels, and a length limit of 2 Gigabytes.
Photoshop files sometimes have the file extension .PSB, which stands for “Photoshop Big” (also known as “large document format”). A PSB file extends the PSD file format, increasing the maximum height and width to 300,000 pixels and the length limit to around 4 Exabytes. The dimension limit was apparently chosen somewhat arbitrarily by Adobe, not based on computer arithmetic constraints (it is not close to a power of two, as is 30,000) but for ease of software testing. PSD and PSB formats are documented.
Because of Photoshop’s popularity, PSD files are widely used and supported to some extent by most competing software. The .PSD file format can be exported to and from Adobe Illustrator, Adobe Premiere Pro, and After Effects, to make professional standard DVDs and provide non-linear editing and special effects services, such as backgrounds, textures, and so on, for television, film, and the web. Photoshop’s primary strength is as a pixel-based image editor, unlike vector-based image editors. However, Photoshop also enables the creation, incorporation, and manipulation of vector graphics through its Paths, Pen tools, Shape tools, Shape Layers, Type tools, Import command, and Smart object functions. These tools and commands are convenient when you want to combine pixel-based and vector-based images in one Photoshop document, because you may not have to use more than one program. However, if you want to create very complex vector graphics with numerous shapes and colors, you may find it easier to use software that was created primarily for that purpose, such as Adobe Illustrator, CorelDRAW or Xara Designer Pro. If you want to import the complex vector object into Photoshop, you can import it as a Smart Object. Double-click on Photoshop’s layers palette to open the object in its original software, such as Adobe Illustrator. You can make changes. When you save, Photoshop will update the Smart Object.