Raster and Vector Artwork in Photoshop CC
The vast majority of the artwork with which you work (or play) in Photoshop is raster artwork. Raster imagery consists of uniformly sized squares of color (pixels), placed in rows and columns (the raster).
Digital photos, scanned images, and just about anything that you put on a layer in Photoshop consists of pixels. When you edit the image, you’re changing the color of the individual pixels, sometimes in subtle ways and sometimes in dramatic ways.
Vector artwork is a horse of another color. Rather than pixels, vector art consists of a mathematically defined path to which you add color. In Photoshop, as in Adobe Illustrator, the path produces the shape of the object, and you can add color both along the path (stroke), within the path (fill), to make the shape become an object.
This figure shows a fine example of vector artwork. Observe that each element in the image consists of a single color. Each section of the image is easily identifiable as an individual object, consisting of a specific color. (Remember, though, that vector objects can be filled with gradients rather than color.)
Each element in the artwork is defined by its path, which consists of a number of path segments. In the figure, you see the path that defines the tongue.
When artwork is defined by pixels, the little square corners of the individual pixels can be noticeable along curves and diagonal lines. With vector artwork, the path is sharp and the edges are well defined. However, to truly get the best appearance from vector art or vector type, the artwork must be printed to a PostScript-capable device, such as a laser printer.
PostScript is a page-description language that takes advantage of the mathematical descriptions of vector art. When you print to an inkjet printer, the vector art is converted to pixels. If you print to such a non-PostScript device, use a high image resolution for best output — 300 pixels per inch (ppi) is usually good.
If you know you’ll be outputting to a non-PostScript device, before you start creating shapes, go to Photoshop’s Preferences→General and make sure to select Snap Vector Tools and Transformation to Pixel Grid.
A vector path can be scaled (changed in size) almost infinitely without losing its appearance. A vector logo can be used for both a business card and a billboard without loss of quality because the path is mathematically scaled before the stroke or fill is added. Raster art, on the other hand, can be severely degraded by such scaling.
For a simple demonstration of the difference between scaling rasterized text and scaling Photoshop’s vector type, see this figure.