FRAME 00000 • 00:00:00 • LINE 240/525
▶ SHOW SIGNAL REFERENCE

◈ FULL WAVEFORM PROCESSING

Unlike simplified NTSC emulators, this lab applies all filters to the entire waveform:

  • Bandwidth limiting affects sync, burst, porches AND active video
  • Noise is injected across the complete signal — not just visible areas
  • The waveform monitor shows pre-filter (dashed) vs post-filter (solid) traces
  • You can see how filters round sync edges, attenuate colorburst, and shape active video

◈ CGA COMPOSITE COLOR

IBM CGA's 14.318 MHz pixel clock is exactly 4× the NTSC color subcarrier. This means:

  • Every 4 pixels = 1 color clock cycle
  • Alternating 1-pixel columns create artifact colors beyond the 4-color palette
  • The famous "composite CGA" trick gave games like King's Quest 16+ colors on a TV
  • Different alternating patterns (01, 10, 0110, 1001) each produce distinct artifact hues

◈ APPLE II ARTIFACT COLOR

The Apple II generates all color through NTSC artifacts:

  • A pixel on an even column → violet artifact
  • A pixel on an odd column → green artifact
  • Two adjacent pixels → white
  • The 7th bit of each byte shifts palette to blue/orange
  • No hardware color generation — it's all NTSC crosstalk!

◈ NES PPU COLOR

The NES PPU generates color by manipulating NTSC chroma phase directly:

  • 12 hues at 30° intervals around the color wheel
  • 4 brightness levels (columns $x0-$xD)
  • Emphasis bits (R/G/B) darken specific phases
  • Colors $x0 = gray ramp, $xD = black, $xE/$xF = blacker-than-black

◈ CROSS-COLOR ARTIFACTS

Because luma and chroma share bandwidth around 3.58 MHz:

  • Cross-Color: High-freq luma → false color (rainbow on stripes)
  • Cross-Luminance: Chroma → visible dot crawl pattern
  • Notch filter TVs have worst artifacts (but CGA needs them!)
  • Comb filters cancel artifacts by comparing adjacent lines

◈ SIGNAL STRUCTURE

Each scan line of an NTSC signal lasts ~63.5µs and contains:

  • Front Porch (~1.5µs) — Voltage stabilization
  • Sync Pulse (~4.7µs) — Horizontal sync at -40 IRE
  • Colorburst (~2.5µs) — 8-10 cycles of 3.58MHz reference
  • Active Video — Luminance + QAM chrominance