On computer displays, a computer icon is a small pictogram. Icons have been used to supplement the normal alphanumerics of the computer. Modern computers now can handle bitmapped graphics on the display terminal, so the icons are widely used to assist users. A computer icon usually ranges from 16 by 16 pixels up to 128 by 128 pixels. Some operating systems feature icons up to 512 by 512 pixels. When the graphical output device has a smaller size, the icon size is small. Vision impaired users (due to such conditions as poor lighting, tired eyes, medical impairments, bright backgrounds, or colour blindness) may need to utilize the self-selected icon size options.