File:NTSC video ragged box.png: Difference between revisions

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(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)
 
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How an [[NTSC video]] signal gets generated in the PPU and decoded by the TV
How an [[NTSC video]] signal gets generated in the PPU and decoded by the TV


Horizontal scale: 1 diagram pixel = 1 NTSC [[clock rate|master clock]] (21.5 MHz) cycle; 4 diagram pixels = 1 NES pixel; 6 diagram pixels = 1 color subcarrier cycle
Horizontal scale: 1 diagram pixel = 1 NTSC [[Cycle_reference_chart#Clock_rates|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
Top row: what goes on in the NES PPU

Latest revision as of 05:52, 20 November 2018

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.

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