The picture uses 480 active vertical lines, the visible part of the 525-line raster built for National Television System Committee (NTSC) color television. The number in the name is that line count, not the width. The letter i means each frame is two fields: the odd lines, then the even lines. That split is how Standard Definition (SD) television filled a screen while sending only half the lines at a time. The lines left over in the 525-line raster are vertical blanking, not picture.
How Two Fields Make One Frame
A field is one pass of every other line. The next field fills the lines the first skipped, and the pair is one frame. Color timing sits a hair under a round count, at 59.94 fields per second, so the frame rate is 29.97 Frames Per Second (FPS). The two fields are not the same instant. They are about a sixtieth of a second apart.
- Odd field. Lines 1, 3, 5, and so on, through the active picture.
- Even field. Lines 2, 4, 6, and so on, arriving one field later and completing the frame.
- Combing. If the subject moved between those two times, weaving the fields leaves horizontal teeth. A display hides them by dropping one field, blending the pair, or estimating the missing lines.
Drawing all 480 lines in one pass is 480 Progressive (480p). Progressive scan spends a full frame on every tick, commonly near 59.94 frames per second, so motion does not depend on weaving two times together. Interlace sends less picture information for the same vertical count, at the cost of that weave. Diagrams put the odd lines first. Some tape and disc systems store the opposite field order, but the frame is still the pair.
Pixels, Shape, and the Fractional Rate
For 480i, a digital copy usually stores about 720 by 480 pixels. Those samples are not square. A square-pixel 4:3 picture at this height would be 640 pixels wide, and a square-pixel 16:9 picture would be about 854 pixels wide. The stored width sits between those two, so the player squeezes the grid onto a 4:3 screen or stretches it onto a 16:9 screen. Shown as square pixels, a 4:3 picture looks too wide and a 16:9 picture looks too tall.
The field rate is 59.94 rather than 60 because color had to slow the black-and-white timing by one part in 1,001. Half of that field rate is the 29.97 frame rate. Round numbers are close enough for a label, and they are wrong for exact timing.
The 50 Hz counterpart stores about 720 by 576 and scans at 50 fields per second, which is 25 frames. That mode is 576 Interlaced (576i), the standard-definition picture used with Phase Alternating Line (PAL). Its one-pass partner is 576 Progressive (576p).
Scan Modes That Came After
High Definition (HD) raised the line count and split into two habits. 720 Progressive (720p) paints every line each frame. 1080 Interlaced (1080i) keeps the two-field idea, with 1,080 active lines instead of 480.
1080 Progressive (1080p) is the one-pass version of that line count, also called Full High Definition (FHD). The next common step in computers and television is 1440 Progressive (1440p), also called Quad High Definition (QHD).
Above that, 2160 Progressive (2160p) is the usual Ultra High Definition (UHD) raster, and 4320 Progressive (4320p) is the mode labeled 8,000 Pixels (8K). None of these later progressive modes needs a second field to finish a frame.
Disc archives, older cameras, and some cable boxes still emit 480i. A High-Definition Multimedia Interface (HDMI) connection can pass that timing through, and the display then rebuilds a progressive frame for its pixel grid. The number on every row below is still the active vertical line count. The scan column says whether those lines arrive as two fields or as one pass.
| Mode | Vertical Lines | Typical Pixels | Scan | Usual Rate | Usual Role |
| 480i | 480 | 720×480 | Interlaced | 59.94 fields (29.97 frames) | NTSC standard-definition broadcast and disc |
| 480p | 480 | 720×480 | Progressive | 59.94 frames | Progressive standard definition |
| 576i | 576 | 720×576 | Interlaced | 50 fields (25 frames) | 50 Hz standard-definition broadcast |
| 576p | 576 | 720×576 | Progressive | 50 frames | Progressive standard definition at 50 Hz |
| 720p | 720 | 1280×720 | Progressive | 50 or 59.94 frames | High-definition progressive |
| 1080i | 1,080 | 1920×1080 | Interlaced | 50 or 59.94 fields | High-definition interlaced broadcast |
| 1080p | 1,080 | 1920×1080 | Progressive | 24 to 60 frames | Full high definition |
| 1440p | 1,440 | 2560×1440 | Progressive | Typically 60 frames | Quad high definition |
| 2160p | 2,160 | 3840×2160 | Progressive | 24 to 60 frames | Ultra high definition raster |
| 4320p | 4,320 | 7680×4320 | Progressive | 24 to 60 frames | Finest common television raster |