(Folk who use the metric system will prefer points and dots per centimeter.) The density of an image refers to how that resolution is mapped onto something you’re viewing, and it’s measured in pixels per inch (ppi), even though you’ll likely see it referred to as dots per inch (dpi). In this image, the 72 dpi and 144 dpi have the same resolution, but are mapped at different scales. Density, typically in ppi, is how resolution is mapped to scale on a display or when printing. Resolution defines how much information or distinct detail is in an image, measured in pixels. You might need quite a lot of pixels to provide a zoomable image of something with a lot of detail, like a machine, or to print a large-format photograph. The amount of detail you capture in an image-whether a photo, scan, or graphic-is directly related to its resolution, as to capture ever more detail, you need ever more pixels. Resolution refers effectively to the amount of information in an image, and more concretely to its dimensions measured in pixels. How can you tell the difference and provide what’s needed? Resolution and image pixel density are two separate concepts often blurred into the single term “resolution.” This makes it difficult to provide what’s needed. Some purposes require high-resolution images.
