This chapter described the importance of image resolution and how to resize images and maintain image quality. Following are key concepts:
A bitmap, or raster, image gets its detail from the number of pixels it contains, which is referred to as resolution and measured in pixels per inch (ppi). Higher resolution usually translates into greater detail; lower resolution usually translates into less detail. Vector images are resolution-independent, while combination bitmap-and-vector images are resolution-dependent. Image resolution for bitmap and combination bitmap-and-vector images should usually be 300 ppi for print, 72 ppi for the Web. Ideally, pixels should be captured initially, not added later.
You can choose ImageImage Size to resize entire images. Unchecking the Resample Image box in the Image Size dialog box when you increase size or resolution numbers ensures that you don't degrade image quality when resizing with the Image Size command. You can choose ImageCanvas Size to resize the canvas, or background, and EditTransform to resize parts of images.