How Wozniak Made the Apple II Display Color Graphics

Steve Wozniak's 1977 patent for a circuit that allowed a home computer to display stable, sharp color graphics on a standard television screen.

What it covers

This patent describes a timing circuit that synchronizes a computer's digital signals with the analog signal requirements of a standard television. Because televisions use a specific color frequency (the color subcarrier), simply outputting digital data often resulted in blurry or 'crawling' colors. Wozniak's invention uses a horizontal synchronization counter that is locked to an odd-submultiple of the color frequency. By introducing a specific 'delayed' count into this cycle, the system ensures that the color phase remains consistent across different scan lines, preventing the color distortion that would otherwise occur on a consumer CRT display.

What it doesn't cover

• —Does not cover non-raster scan display technologies like modern LCD or OLED panels.
• —Does not cover software-based color generation methods that do not rely on hardware-level timing synchronization.
• —Does not cover high-definition (HD) or 4K signal timing protocols.
• —Does not cover the specific logic used to store the pixel data itself, only the timing synchronization for the output.

The clever bit

Wozniak realized that if you force the computer's horizontal sync to be an odd-submultiple of the color subcarrier, the phase of the color signal automatically corrects itself every other line, eliminating the need for complex and expensive external hardware.

Why it matters

This patent was the technical backbone of the Apple II, the machine that effectively launched the personal computer industry. By allowing the Apple II to plug into an affordable, off-the-shelf television instead of an expensive professional monitor, Wozniak made home computing commercially viable for the first time.

Real-world examples

• 1.Apple II personal computer
• 2.Early home video game consoles using NTSC television signals