The composite video signal combines luminance (brightness), chrominance (color), and synchronization signals into a single waveform. The signal includes horizontal and vertical sync pulses that tell the TV when to start each new line and frame. This ingenious encoding allowed a single wire to carry a complete picture.

The Y signal represents brightness, varying from 0V (black) to ~0.7V (white). This is the signal that monochrome TVs use — it's the complete picture in grayscale. The human eye is most sensitive to luminance detail, so this channel gets the full bandwidth (~4.2 MHz for NTSC).

Rather than sending R, G, B separately, color TV encodes two color-difference signals: U (B−Y) and V (R−Y). These are zero for grayscale content, saving bandwidth. The green signal is mathematically derived from Y, U, and V at the receiver. Clever, right?

U and V are combined onto a single subcarrier using QAM — they modulate the same frequency but 90° apart in phase. The receiver uses synchronous demodulation to separate them. The colorburst on each line provides the phase reference needed for this magic trick.

NTSC (3.58 MHz, 525 lines, 29.97fps): Susceptible to hue errors — hence "Never The Same Color." PAL (4.43 MHz, 625 lines, 25fps): Reverses color phase each line, averaging out errors. SECAM (625 lines, 25fps): Uses frequency modulation for color, sending U and V on alternate lines.

Three electron guns fire beams at phosphor dots on the screen — one each for red, green, and blue. A shadow mask ensures each beam only hits its color's phosphors. Magnetic deflection coils sweep the beams across and down the screen 50 or 60 times per second, painting the image line by line.