Display resolution

Display standards comparisonThe display resolution of a digital television or computer display typically refers to the number of distinct pixels in each dimension that can be displayed. It can be an ambiguous term especially as the displayed resolution is controlled by different factors in cathode ray tube (CRT) and flat panel or projection displays using fixed picture-element (pixel) arrays.

One use of the term "display resolution" applies to fixed-pixel-array displays such as plasma display panels (PDPs), liquid crystal displays (LCDs), digital light processing (DLP) projectors, or similar technologies, and is simply the physical number of columns and rows of pixels creating the display (e.g., 800×600 or 1024×768). A consequence of having a fixed grid display is that for multiformat video inputs all displays need a "scaling-engine" (a digital video processor that includes a memory array) to match the incoming picture format to the display.

Considerations
Some commentators also use this term to indicate a range of input formats that the display's input electronics will accept and often include formats greater than the screen's native grid size even though they have to be down-scaled to match the screen's parameters (e.g., accepting a 1920×1080 input on a display with a native 1366×768 pixel array). In the case of television inputs, many manufacturers will take the input and zoom it out to "overscan" the display by as much as 5% so input resolution is not necessarily display resolution.

The eye's perception of "display resolution" can be affected by a number of factors—see Image resolution and Optical resolution. One factor is the display screen's rectangular shape, which is expressed as the ratio of the physical picture width to the picture height. This is known as the aspect ratio. A screen's physical aspect ratio and the individual pixels' aspect ratio may not necessarily be the same. An array of 1280×720 on a 16:9 display has square pixels. An array of 1024×768 on a 16:9 display has rectangular pixels.

An example of pixel shape affecting "resolution" or perceived sharpness: displaying more information in a smaller area using a higher resolution makes the image much clearer. However, newer LCD displays and such are fixed at a certain resolution; making the resolution lower on these kinds of screens will greatly decrease sharpness, as an interpolation process is used to "fix" the non-native resolution input into the displays native resolution output.

While some CRT-based displays may use digital video processing that involves image scaling using memory arrays, ultimately "display resolution" in CRT-type displays is affected by different parameters such as spot size and focus, astigmatic effects in the display corners, the color phosphor pitch shadow mask (such as Trinitron) in color displays, and the video bandwidth.

Overview
Analog television systems use interlace scanning with two sequential scans (50 or 60 fields per second), one with the odd numbered lines, the other with the even numbered lines to give a complete picture (25 or 30 frames per second). This is done to save transmission bandwidth but a consequence is that in picture tube (CRT) displays, the full vertical resolution cannot be realized. For example, the maximum detail in the vertical direction would be for adjacent lines to be alternately black then white. This is not a problem in a progressive display but an interlace display will have an unacceptable flicker or twitter at the slower frame rate. This is why interlace is unacceptable for fine detail such as computer word processing or spreadsheets. For television it means that if the picture is intended for interlace displays the picture must be vertically filtered to remove this objectionable flicker with a reduction of vertical resolution to about 70%. So a 576 line PAL interlace display only has about 400 lines vertical resolution and 350 in the case of a 486 line NTSC interlace display (486i visible out of 525 lines). Similarly, 1080i HD interlaced video would need to be filtered to about 700 lines for an interlaced display. Any interlaced broadcast television pictures and for that matter DVDs are filtered to that vertical resolution to reduce the interline twitter on fine detail.

Fixed pixel array displays such as LCDs, plasmas, DLPs, LCoS, etc. need a "scaling" processor with frame memory, which, depending on the processing system, effectively converts an incoming interlaced picture into progressive. A similar process occurs in a PC and its display with interlaced video (e.g., from a TV tuner card). The downside is that interlace motion artifacts are almost impossible to remove resulting in horizontal "toothed" edges on moving objects.

Also in analog connected picture displays such as CRT TV sets, the horizontal scanlines are not divided into pixels, and therefore the horizontal resolution is related to the bandwidth of the luminance and chroma signals. For television, the analog bandwidth for luminance in standard definition should be flat to 5 MHz and in high definition, about 30/31 MHz.

Current standards

 
Image:Aspect Ratios and ResolutionsTelevisions are of the following resolutions:

SDTV: 480i (640 x 480), EDTV: 480p (720 x 480), HDTV: 720p (1280 x 720), HDTV: 1080i (1920 x 1080).

Computers have higher resolutions:

Currently 1024×768 Extended Graphics Array is the most common display resolution.[1] Many computer users including CAD users, graphic artists and video game players run their computers at 1600×1200 resolution (UXGA, Ultra-eXtended) or higher if they have the necessary equipment—although 1280×1024 (SXGA Super eXtended Graphics Array) is more widespread as it is the optimum resolution of most 19-inch monitors. Other recently available resolutions include oversize aspects like 1400x1050 SXGA+ and wide aspects like 1280x720 WXGA, 1680x1050 WSXGA+, and 1920x1200 WUXGA.

When a computer display resolution is set higher than the physical screen resolution, some video drivers make the virtual screen scrollable over the physical screen. Most LCD manufacturers do make note of the panel's native resolution as working in a non-native resolution on LCDs will result in a poorer image, due to interpolation. Some CRT monitors will accept higher resolutions than their specified native resolution. Few CRT manufacturers will quote the true native resolution since CRTs are analog in nature and can vary their display from as low as 320x200 (emulation of older computers or game consoles) to as high as the internal CRT design will allow. Thus CRTs provide a variability in resolution that LCDs can not provide (LCDs are fixed resolution).