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Screen Resolutions and Video Formats

Please make sure you also read the page on frame rates since screen resolution and frame rate are connected: a game running at a lower resolution (eg. 320x200) will attain a higher frame rate due to the larger pixel fill per area capability, but the image must then be scaled up to fit the screen (eg. 640x480). The game will be faster, but the user will see a much lower quality image.

The following is from the IRIS Digital Media Programmers' Guide, Chapter 3, 'Video Basics'. It describes the various video formats and their demographic uses.

Broadcast Standards

Broadcast standards, or video timing formats, are ways of encoding video information for broadcast to television receivers. These standards are also used to describe the display capabilities of video monitors and are thus also called video timing formats or video output formats (VOFs). The three broadcast standards are:


Named after the National Television Systems Committee, which developed it, this standard is used in all of North and South America, except Brazil, and in much of East Asia.

PAL (Phase Alternated by Line)

This standard is used in western Europe, including the United Kingdom but excluding France, and in East Asia, including Australia.

SECAM (Sequentiel Couleur avec Memoire)

This standard is used in France, eastern Europe, the Near East and Mideast, and parts of Africa and the Caribbean.

Note: NTSC implementations can vary slightly by country; PAL and SECAM implementations can vary considerably.

NTSC employs a total of 525 horizontal lines per frame, with two fields per frame of 262.5 lines each. Each field refreshes at 60Hz (actually 59.94Hz). NTSC encodes brightness, color, and synchronizing information in one signal.

PAL employs a total of 625 horizontal lines per frame, with two fields per frame of 312.5 lines per frame. Each field refreshes at 50Hz. PAL encodes brightness, color, and synchronizing information in one signal also, but in a different way from NTSC.

SECAM transmits the same number of lines at the same rate as PAL, but transmits each color difference signal on alternate lines, using the frequency modulation of the subcarrier.

These numbers of horizontal lines (525 and 625, respectively) are a shorthand description of what actually happens. For NTSC, the first (odd) field starts with a whole line and ends with a half line; the second (even) field starts with a half line and ends with a whole line. Each NTSC field contains 242.5 active lines and 20 lines of vertical blanking.

Similarly, for PAL, the first (even) field starts with a half line and ends with a whole line; the second (odd) field starts with a whole line and ends with a half line. Each PAL field contains 287.5 active lines and 25 lines of vertical blanking.

In each case, the numbers 525 and 625 refer to transmitted lines; the active video lines are fewer; typically, 485 for NTSC and 575 for PAL. The remaining lines are used for delimiting frame boundaries and for synchronization and other information.

To minimize frame flickering and reduce the bandwidth of the video signal, the active video lines are interlaced, as explained earlier in this chapter.

NTSC and PAL can be recorded digitally; these recording techniques are referred to as D2 525 (digital NTSC) and D2 625 (digital PAL).

Videotape Formats

Videotape recorders are available for analog and digital recording in various formats. They are further classified by performance level, or market: consumer, professional, and broadcast. In addition, during postproduction (editing, including addition of graphics), the original footage can be transferred to digital media; digital videotape formats are available for composite and component video formats. There are no official standards for videotape classifications. Table 11-1 summarizes the formats:

Electronics    Consumer     Professional       Broadcast      Postproduction

Analog       VHS cassette    U-Matic (SP)    Type C reel-to- 
              (composite)   cassette, 3/4-    reel, 1-inch
                                inch         (composite)

                S-VHS                        Type B (Europe)
           (YC, composite)                    (composite)

               S-Video        S-Video 
               (YC-358)       (YC-358)

                Beta         Hi-8mm (YC)       Betacam
             (composite)                      (component)

                8mm                            Betacam SP
             (composite)                       (YUV, YIQ,

              Hi-8mm                               MII
           (YC, composite)                     (YUV, YIQ,

Digital                                                       D1 525 (YUV)
                                                              D1 625 (YUV)
                                                              D2 525 (NTSC)
                                                              D2 625 (PAL)

Table 11-1 Tape Formats and Video Formats

Most home VCRs use composite connectors. S-Video, on the other hand, carries the color and brightness components of the picture on separate wires; hence, S-Video connectors are also called Y/C connectors. Most S-VHS and Hi-8mm VCRs feature S-Video connectors.

In other words, US TV is at a lower resolution but a higher frame rate than PAL TV, a simple trade-off.

Note that both formats have the same aspect ratio, ie. 640:480 is the same ratio as 768x576, namely 4:3.


The N64 is said to be HDTV compatible, but what does this mean? Certainly, as the N64 currently stands, it could not render images at HDTV resolution (typically either 1600x1200, 1920x1035 or 1920x1152) - there simply isn't enough memory in the machine to do it. This leads me to draw the following conclusion: since the existing N64 hardware cannot output HDTV, it is highly likely that future support will be in the form of an adaptor unit of some kind, which will probably include the replacement of the memory expansion kit in the top of the machine by something with a larger capacity. It would be very nice if such an adaptor would support mid-range resolutions such as SVGA and XGA, combined with the ability to use the console with standard monitors. Whether this will be the case is completely unknown.

Image Quality

A high resolution image doesn't necessarily mean a better image quality. SGI Doom can run at 320x200, 640x400, 960x600 or 1280x800 resolution, but the latter three modes are merely the normal 320x200 PC resolution scaled up by a factor of 2, 3 or 4. When full screen, the image looks identical to PC Doom. The only real difference is hidden: at 960x600, the pixel fill rate is about 19 times that of a PC running at 320x200 (according to Dave Taylor of Id Software), yet the frame rate is usually still the same.

When it comes to games consoles, even though the TV display may be (for example) 640x480, it's entirely possible that the game itself is being rendered at 320x200, after which the image is scaled up to the correct TV resolution. There is always a temptation in video game design to render at a lower resolution because it allows for a higher frame rate (due to higher available pixel fill rate per unit area and lower use of memory), but as this is at the expense of image quality I sincerely hope that we'll see less and less of this in the future.

Few gamers reading this will ever have seen an HDTV display, but if you have then you'll appreciate the difference in image quality that the higher resolution(s) can give. For games, it's important for genres that require visual realism, eg. flight sims and racing games.

Digital TV has been slow to take off in the West, as has HDTV. At some point, hopefully, NOA/SGI will decide the time is right and release an HDTV adaptor. Personally, I don't expect this to happen before 2001, but after seeing high-end SGI simulations running at 1600x1200, I sincerely hope it's sooner rather than later.

Ian's SGI Depot: FOR SALE! SGI Systems, Parts, Spares and Upgrades

(check my current auctions!)
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