Images may have more colors than the monitor can show or details too small for the pixels to render. That's where dithering and antialiasing come in. Dithering Monitors and image files limited to 256 colors can create the illusion of more colors by dithering the available colors in a diffuse pattern of pixels, approximating the desired color. Dithering is used by operating systems and display applications, such as Web browsers, running on 8-bit monitors.
Image editors use dithering to convert true-color images to indexed colors.
Because it can look bad in some situations, most image editors make dithering an option . The alternative to dithering is color substitution , which uses the closest color on the palette. Antialiasing All computers and printers, regardless of color depth, render pixels in a grid. This creates problems for images that aren't grid-shaped. The strict division between pixels is called alias, so certain applications use antialiasing to smooth out the image .