The transition to high-density pixel displays that began with smartphones and tablets has spread to the computer monitors. 4K PC screens appeared in 2014, and understanding pixel density has become important when choosing a product, along with screen size and resolution. Retina monitors sold by Apple are generally recognized as having a physical pixel density greater than 200 pixels per inch (PPI). This means that they have twice the pixel density of a classic resolution computer monitor. Smartphones and tablets are the main drivers for this trend due to their low cost and high pixel density, which is usually higher than 250 PPI. This means that the average person cannot see individual pixels on a high-density screen, 10-15 inches away on a smartphone or tablet, or 20 inches on a laptop or computer screen. The number of device pixels that make up a CSS pixel in one direction is its Device Pixel Ratio (DPR). When something like full-screen display or enlarged display is used to display an image on an LCD at a resolution other than the recommended one, it can be necessary, for example, to use two pixels to display data that should be shown with one dot. Naturally this leads to a loss of sharpness. Since such deterioration in image quality cannot be avoided, of course the best thing is to display an image at the "native resolution" for the LCD monitor.