Electronic visual display
An electronic visual display, informally a screen, is a display device for presentation of images, text, or video transmitted electronically, without producing a permanent record. Electronic visual displays include television sets, computer monitors, and digital signage. By the above definition, an overhead projector (along with screen onto which the text, images, or video is projected) could reasonably be considered an electronic visual display since it is a display device for the presentation of an images, plain text, or video transmitted electronically without producing a permanent record. They are also ubiquitous in mobile computing applications like tablet computers , smartphones, and information appliances. Types. These are the technologies used to create the various displays in use today. Additionally, Cathode-ray tubes were widely used in the past and microLED displays are under development. Classification. Electronic visual displays present visual information according to the electrical input signal (analog or digital) either by emitting light (then they are called "active displays") or, alternatively, by modulating available light during the process of reflection or transmission (light modulators are called "passive displays"). Display mode of observation. Electronic visual displays can be observed directly ("direct view display") or the displayed information can be projected  to a screen (transmissive or reflective screen). This usually happens with smaller displays at a certain magnification. A different kind of projection display is the class of "laser projection displays", where the image is built up sequentially either via line by line scanning or by writing one complete column at a time. For that purpose one beam is formed from three lasers operating at the primary colors, and this beam is scanned electro-mechanically (galvanometer scanner, micro-mirror array)) or electro-acousto-optically. Layout of picture elements. Depending on the shape and on the arrangement of the picture elements of  a display, either fixed information can be displayed (symbols, signs), simple numerals (7-segment layout) or arbitrary shapes can be formed (dot-matrix displays). Emission and control of colors. Colors can be generated by selective emission, by selective absorption, transmission or by selective reflection. Addressing modes. Each sub-pixel of a display device must be selected (addressed) in order to be energized in a controlled way.