Pixel art is a form of digital art, created through the use of raster graphics software, where images are edited on the pixel level. Graphics in most old (or relatively limited) computer and video games, graphing calculator games, and many mobile phone games are mostly pixel art.
Pixel art is distinguished from other forms of digital art by an insistence upon manual, pixel-level editing of an image (without the application of image filters, automatic anti-aliasing or special rendering modes), often at close magnification. In this form, it is commonly said that “each pixel was placed carefully” to achieve a desired result.
Purists within the pixel art scene hold that “true” pixel art should only be created from tools that place individual pixels (such as the ‘pencil’ tool), and that pixel artists should avoid all other tools including line, Bezier curve, circle and rectangle. Others counter that tools such as line and bucket-fill are acceptable as their functions could be just as easily, if not as quickly, replicated on an individual pixel basis.
Because of this rule, image filters (such as blurring or alpha-blending) or tools with automatic anti-aliasing are considered not valid tools for pixel art, as such tools calculate new pixel values automatically, contrasting with the precise manual arrangement of pixels associated with pixel art.
Images resources from Smashing Magazine