CRT converter

6 CRT types

• NTSC Colour — American colour TV. Runs proper YIQ colour space conversion with chroma compression and warm phosphor cast.
• PAL Colour — European standard. Slightly cooler, more accurate colour reproduction, subtle chroma smear.
• Soviet 3CTAH — SECAM with Soviet-era monitor characteristics: heavily desaturated, greenish phosphor cast, crushed blacks, high noise, severe barrel distortion, long persistence, and burn-in enabled by default.
• P31 Green — the classic green-phosphor terminal (IBM 3270, DEC VT100). Monochrome, luminance-tinted green.
• P26 Amber — amber phosphor screens (Hercules cards, European terminals). Warmer, more burn-in, higher persistence.
• P4 White — cool white phosphor (standard TV tubes, early PC monitors). Higher noise, more barrel distortion.

Adjust the converter to create various typical CRT conversions.

CRT converter

Conversion examples

CRT converter

Interlacing

Interlacing was how CRTs refreshed the screen to avoid flicker without doubling the bandwidth needed.

Instead of drawing all 625 lines top-to-bottom in one pass (progressive scan), an interlaced CRT drew two fields per frame. Field 1 drew all the odd-numbered lines (1, 3, 5...), then Field 2 drew all the even-numbered lines (2, 4, 6...). At 25 frames per second (PAL), this meant the screen was actually refreshing at 50 fields per second — fast enough that your eye perceived it as smooth.

What it looked like on still images: nothing visible. The two fields aligned perfectly and you couldn't tell it was interlaced. Where it became obvious: on moving subjects. Because Field 1 and Field 2 were captured at slightly different moments in time (1/50th of a second apart), a fast-moving object would be in a slightly different position in each field. When the two fields were combined into one frame, the moving edges would show a distinctive comb effect — alternating lines from the two fields offset from each other, looking like horizontal teeth along motion edges.

In the converter, the interlace slider simulates this by randomly dimming alternating scan lines slightly, and at higher values adding a small brightness variation between odd and even lines. This mimics the field shimmer you'd see on a real CRT — particularly noticeable on cameras pointed at CRT screens, or on photographs of televisions.

It's most authentic on the PAL 625-line and NTSC 525-line presets. The Soviet preset has it cranked high because SECAM sets often had poor field sync, making the combing more visible. HDTV 1080i has high interlace too — even in high-definition, 1080i was still interlaced, and fast sports footage on HD CRTs showed the same combing on motion edges.

At low values (0–20) it just adds a very subtle alternating line shimmer that makes the image feel more alive. At high values (60+) you start seeing the comb structure clearly, which looks wrong on a still image but authentic on anything that was shot as video.