Adobe Photoshop is a graphics editing program developed and published by Adobe Systems. 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, transparency, text, alpha channels and spot colors, clipping paths, and duotone settings. A PSD file has a maximum height and width of 30,000 pixels, and a length limit of 3 Gigabytes. Photoshop also enables vector graphics editing through its Paths, Pen tools, Shape tools, Shape Layers, Type tools, Import command, and Smart Object functions. Because of Photoshop's popularity, PSD files are widely used and supported to some extent by most competing software. These tools and commands are convenient to combine pixel-based and vector-based images in one Photoshop document, because it may not be necessary to use more than one program.