File:NTSC video ragged box.png

From NESdev Wiki
Revision as of 22:22, 14 June 2011 by Tepples (talk | contribs) (How an NTSC video signal gets generated in the PPU and decoded by the TV Horizontal scale: 1 diagram pixel = 1 NTSC master clock (21.5 MHz) cycle; 4 diagram pixels = 1 NES pixel; 6 diagram pixels = 1 color subcarrier cycle Top row: wh)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to navigationJump to search

NTSC_video_ragged_box.png(256 × 160 pixels, file size: 2 KB, MIME type: image/png)

How an NTSC video signal gets generated in the PPU and decoded by the TV

Horizontal scale: 1 diagram pixel = 1 NTSC master clock (21.5 MHz) cycle; 4 diagram pixels = 1 NES pixel; 6 diagram pixels = 1 color subcarrier cycle

Top row: what goes on in the NES PPU

  1. Generate the subcarrier for a solid red screen (color $16).
  2. A shape drawn in this color, including a 2-pixel-wide vertical line.
  3. Multiply it by 0 outside of the shape and 1 inside the shape. Notice how the subcarrier protrudes into the shape.

Bottom row: what goes on in the TV when separating luma from chroma

  1. Incoming picture signal on the composite
  2. Impulse response of the low-pass filter
  3. Picture signal convolved with the low-pass filter, used as luma. Notice the ragged left and right sides of the vertical line.

The filter in this diagram is an FIR filter [1 4 7 8 8 8 7 4 1]/48, which factors to [1 1][1 1][1 1][1 1 1][1 0 0 1]/48. A real TV might use a Bessel filter (near-linear-phase IIR filter), but the principle is the same: filter out anything above 3 MHz.

Permission is granted to use this copyrighted illustration under the WTFPL.

File history

Click on a date/time to view the file as it appeared at that time.

Date/TimeThumbnailDimensionsUserComment
current21:56, 21 September 2021Thumbnail for version as of 21:56, 21 September 2021256 × 160 (2 KB)>Maintenance script== Summary == Importing file

There are no pages that use this file.