What is Display Resolution?

The display resolution of a digital television or display device is 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 all 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., 1920×1200). A consequence of having a fixed grid display is that, for multi-format 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.
Note that the use of the word resolution here is a misnomer, though common. The term “display resolution” is usually used to mean pixel dimensions, the number of pixels in each dimension (e.g., 1920×1200), which does not tell anything about the resolution of the display on which the image is actually formed: resolution properly refers to the pixel density, the number of pixels per unit distance or area, not total number of pixels. In digital measurement, the display resolution would be given in pixels per inch. In analog measurement, if the screen is 10 inches high, then the horizontal resolution is measured across a square 10 inches wide. This is typically stated as "lines horizontal resolution, per picture height;" for example, analog NTSC TVs can typically display 486 lines of "per picture height" horizontal resolution, which is equivalent to 648 total lines of actual picture information from left edge to right edge. Which would give NTSC TV a display resolution of 648x486 in actual lines/picture information, but in "per picture height" a display resolution of 486x486.

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 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. According to the Kell factor the reduction is to about 85%, so a 576 line PAL interlace display only has about 480 lines vertical resolution, and a 486 line NTSC interlace display has a resolution of approximately 410 lines vertical. Similarly, 1080i digital interlaced video would need to be filtered to about 910 lines for an interlaced display, although a fixed pixel display (such as LCD) eliminates the inaccuracies of scanning, and thus can achieve Kell factors as high as 95% or 1020 lines.
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.
In analog connected picture displays such as CRT TV sets, the horizontal scanlines are not divided into pixels, but by the sampling theorem, the bandwidth of the luma and chroma signals implies a horizontal resolution. For television, the analog bandwidth for luminance in standard definition can vary from 3 MHz (approximately 330 lines edge-to-edge; VHS) to 4.2 MHz (440 lines; live analog) up to 7 MHz (660 lines; DVD). In high definition the bandwidth is 37 MHz (720p/1080i) or 74 MHz (1080p/60).