Display resolution

The display resolution of a digital television or computer display can be an ambiguous term especially as displayed resolution is controlled by different factors in picture-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 flat-panel plasmas (PDPs), LCDs, front and rear projectors using LCD, DLP or similar technologies and is simply the physical number of columns and rows of pixels creating the display (eg, 852x480; 1368x768 etc). 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.

Some manufacturers 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- (eg. accepting a 1920x1080 input on a display with a native 1368x768 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 isn't 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 1280x720 on a 16:9 progressive scanned display has square pixels.

An example of pixel shape affecting "resolution" or peceived sharpness: if you had 2 similar displays, both the same picture height and both having a 720x576 pixel array but one a 16:9 wide screen, the other a 4:3 screen and you displayed the same 720x576 4:3 picture on both, apart from the picture being stretched on the 16:9 display, the 4:3 screen will look the sharper.

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

Applying mainly to CRT displays the way the lines or rows are displayed will also affect the perceived resolution in the vertical direction. This relates to the differences produced by interlace or progressive scanning and now by the use of memory to hold each pixel's displayed brightness values between picture refreshes.

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 realised. 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 objectional 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 480 line NTSC interlace display. 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 (eg. 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 MHz.

Current Standards in Resolution

Currently 1024×768 (XGA/XVGA, eXtended), 1280×1024 (SXGA Super eXtended Graphics Array), and 1600×1200 resolution (UXGA, Ultra-eXtended) are the most common display resolutions. Many computer users, including CAD users and video game players, run their computers at 1600×1200 resolution (UXGA, Ultra-eXtended) or higher if they have the necessary equipment. When a computer display resolution is set higher than the physical screen resolution, some systems make the virtual screen scrollable over the physical screen, however, most CRT monitors will accept higher resolutions than their native resolution without scrolling. The true maximum resolution is calculated from the dot pitch. Few CRT manufacturers will quote the true native resolution in their documentation, but most LCD manufacturers do. With digital television and HDTV, vertical resolutions of 720 or 1080 scan lines are typical.

Overscan

Most television display manufacturers "overscan" the pictures on their displays (CRTs and PDPs, LCDs etc.), so that the effective on-screen picture may be reduced from 720×576(480) to 680×550(450), for example. The size of the invisible area somewhat depends on the display device. Computer displays including projectors generally do not overscan.

Evolution of Resolution Standards

Many personal computers introduced in the late 1970s and the 1980s were designed to use television sets as their display devices, making the resolutions dependent on the television standards in use, including PAL and NTSC. Picture sizes were usually limited in order to ensure the visibility of all the pixels in the major television standards and the broad range of television sets with varying amounts of overscan. The actual drawable picture area was therefore somewhat smaller than the whole screen, and was usually surrounded by a static-colored border. Also, the interlace scanning was usually omitted in order to provide more stability to the picture, effectively halving the vertical resolution in progress. 320×200 and 640×200 were relatively common resolutions in the era. In the PC world, these resolutions came to be used by the Color Graphics Adapter.

The 640×480 resolution, introduced with the IBM PS/2 VGA and MCGA (multi-color) on-board graphics chips, was the standard resolution in the IBM PC compatibles from 1990 to around 1996, partly due to its 3 ratio. 800×600 was the standard resolution until around 2000. Since then, 1024×768 has been the standard resolution. Many web sites and multimedia products are designed for this resolution. Most of today's computer games released during the "128-bit video game era", such as SimCity 4, do not support 640×480 at all. Microsoft Windows XP is designed to run at 800×600 minimum (although it is possible to select 640×480 in the Advanced Settings window, and an application is able to switch to any other mode). GNU/Linux, FreeBSD, and most Unix variants use The X Window System and can run at any desired resolution as long as the display and video card support it. The Apple's Mac OS and Mac OS X operating systems are able to run with most available display resolutions, although 800×600 is a reasonable minimum.

Common Display Resolutions

Computer Graphics

Computer Standard	Resolution	Display Aspect Ratio	Pixels
VIC-II multicolor, IBM PCjr 16-color	160×200	4:5	32,000
TMS9918, ZX Spectrum	256×192	4:3	49,152
CGA 4-color, Atari ST 16 color, VIC-II HiRes, Amiga OCS NTSC LowRes	320×200	8:5	64,000
QVGA	320×240	4:3	76,800
Amiga OCS PAL LowRes	320×256	5:4	76,800
Black & white Macintosh (9")	512×342	3:2	175,104
Macintosh LC (12")/Color Classic	512×384	4:3	196,608
Atari ST 4 color, CGA mono, Amiga OCS NTSC HiRes	640×200	16:5	128,000
Amiga OCS PAL HiRes	640×256	5:2	163,840
EGA	640×350	64:35 (approx. 9:5)	224,000
Atari ST mono, Amiga OCS NTSC interlaced	640×400	8:5	256,000
VGA and MCGA	640×480	4:3	307,200
Amiga OCS PAL interlaced	640×512	5:4	327,680
HGC	720×348	60:29 (approx. 2:1)	250,560
MDA	720×350	72:35 (approx. 2:1)	252,000
Apple Lisa	720×360	2:1	259,200
WGA	800×480	5:3	384,000
SVGA	800×600	4:3	480,000
XGA	1024×768	4:3	786,432
NeXTcube	1120×832	35:26 (approx. 4:3)	931,840
XGA+	1152×864	4:3	995,328
SXGA	1280×1024	5:4	1,310,720
WXGA	1366×768	16:9	1,049,088
WSXGA or WXGA+	1440×900	16:10	1,296,000
SXGA+	1400×1050	4:3	1,470,000
WSXGA	1600×1024	25:16	1,638,400
WSXGA+	1680×1050	16:10	1,764,000
UXGA	1600×1200	4:3	1,920,000
WUXGA	1920×1200	16:10	2,304,000
QXGA	2048×1536	4:3	3,145,728
WQXGA	2560×1600	16:10	4,096,000
QSXGA	2560×2048	5:4	5,242,880
WQSXGA	3200×2048	25:16	6,553,600
QUXGA	3200×2400	4:3	7,680,000
WQUXGA	3840×2400	16:10	9,216,000
HSXGA	5120×4096	5:4	20,971,520
WHSXGA	6400×4096	25:16	26,214,400
HUXGA	6400×4800	4:3	30,720,000
WHUXGA	7680×4800	16:10	36,864,000

Television/Movies

Analogue TV Standard	Resolution	Display Aspect Ratio	Pixels
PAL (and SECAM)	~350 X 576 lines	4:3	~201600
PalPlus	~350 X 576 lines	16:9	~201600
Undecoded PalPlus	~350 X 432 lines	16:9	~151200
NTSC	~270 X 480 lines	4:3	~129600
Laserdisc	~560×576(480 for NTSC)	4:3	~322560 (268800 for NTSC)
VCR	~240×576(480 for NTSC)	4:3	~138240 (115200 for NTSC)
S-VHS	~400×576(480 for NTSC)	4:3	~230400 (192000 for NTSC)

~ = horizontal resolution is an approximation

Digital Standard	Resolution	Display Aspect Ratio	Pixels
Video CD	352×288(240 for NTSC)	4:3 (non-square pixels)	101376 (84480 for NTSC)
China Video Disc	352×576(480 for NTSC)	4:3 (non-square pixels)	202725 (168960 for NTSC)
SVCD	480×576(480 for NTSC)	4:3 (non-square pixels)	276480 (230400 for NTSC)
EDTV 480p	640×480, 704×480 or 852×480	4:3 or 16:9	307200, 337920, 408960
DVD	704×576(480 for NTSC)	4:3 or 16:9 (non-square pixels)	405504 (337920 for NTSC)
D-1	720×576(480 for NTSC)	4:3 or 16:9 (non-square pixels)	414720 (345600 for NTSC)
D-1 NTSC (square pixels)	720×540	4:3	388800
HDTV 720p	1280×720	16:9	921600
HDTV 1080p	1920×1080	16:9	2073600
HDTV 1080i	1920×1080	16:9	2073600

Digital Film Standard	Resolution	Display Aspect Ratio	Pixels
Academy 4K	3656×2664	1.37:1	9739584
Digital cinema 4K	4096×1714 or 3996×2160	2.39:1 or 1.85:1	7020544, 8631360
Academy 2K	1828×1332	1.37:1	2434896
Digital cinema 2K	2048×858 or 1998×1080	2.39:1 or 1.85:1	1757184, 2157840

External links

Display technology

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