Overview
Fritz Schröter (1886–1973), research director at Telefunken, patented interlaced scanning in 1930: transmitting the odd-numbered lines of a picture in one pass and the even-numbered lines in the next. It halves the bandwidth required for a given perceived flicker rate, and it is the reason broadcast formats still carry an "i" in their names.
What You Need
- Lived: 1886–1973, Germany
- Anchor year: 1930 — the interlacing patent
- Strand: overlooked — universally used, rarely named
Steps
The problem as it stood
Television faced two conflicting demands. Enough lines for a detailed picture, and enough complete pictures per second to avoid visible flicker. Both increase the bandwidth needed, and bandwidth in the 1930s was the scarcest resource in broadcasting. Doubling the frame rate to kill flicker doubled the channel width.
What he actually did
Schröter patented splitting each frame into two fields — all the odd lines, then all the even lines — each transmitted in half the frame time. The eye is presented with a refresh at twice the frame rate, while the total information sent per second is unchanged.
How it worked
Flicker perception depends mainly on how often the screen is refreshed, while perceived detail depends mainly on total line count. Interlacing separates the two: refresh at 50 or 60 fields per second to satisfy the eye, but only 25 or 30 complete frames per second of actual picture information. It is a perceptual trick, exploiting a limit of human vision to save bandwidth — the same logic later codecs would industrialise.
What it made possible
Practical high-definition broadcasting within an allocatable channel. Every analogue broadcast standard used it — 405, 525, 625 lines alike — and it persists in digital formats such as 1080i. It is also the reason interlaced footage looks combed when frozen, and why de-interlacing is still a routine step in video post-production.
What happened to him
Schröter led television research at Telefunken through the 1930s and continued in German electronics research afterwards, publishing widely on television engineering.
Where the credit landed
Interlacing is one of the most consequential ideas in broadcast engineering and one of the least attributed: it is treated as a property of television rather than as somebody's invention. Schröter worked inside Telefunken, so the patent belonged to the company — the assignment mechanism in its ordinary, undramatic form. Anyone who has de-interlaced a clip has used his idea without encountering his name.
Pro Tips
- Interlacing trades temporal resolution for spatial resolution at constant bandwidth.
- The "i" in 1080i is Schröter's patent, still in service.
- Combing artefacts on a freeze-frame are interlacing made visible.
Knowledge Base
What You'll Learn
Interlacing is the first perceptual compression scheme in broadcasting, decades before the word compression was used that way.
Why it is a compression scheme
Later codecs discard information the eye is unlikely to miss — high-frequency detail, subtle colour differences, masked sounds. Interlacing does the same thing structurally: it sends only half the picture at a time and relies on the eye integrating the two halves. When the subject moves quickly the assumption breaks and the two fields disagree, which is exactly why fast motion is where interlacing artefacts appear.
Where This Fits
This guide covers one specific part of the history of media technology. The wider picture — how each link in the chain from capture through transmission to display was actually built, who built it, and why the credit so often landed somewhere else — is in A History of Broadcast Technology: The Chain From Capture to Screen, which frames the discipline as a whole and links out to the detailed guides underneath it, including this one. If you are starting from scratch rather than solving a specific problem, read that first and come back here.
FAQ
Q: Why does interlaced video look combed when paused?
A: A paused frame shows two fields captured at different moments. Anything that moved between them appears displaced on alternate lines, producing the comb pattern. De-interlacing reconstructs a single coherent frame.
Q: Is interlacing still used?
A: Yes. It persists in broadcast formats such as 1080i and in a great deal of archive material, which is why de-interlacing remains a standard post-production step.