{
  "patent_number": "US 3678182",
  "country": "US",
  "title": "How Early Television Systems Isolated Specific Colors for Special Effects",
  "original_title": "Chroma key circuit",
  "summary": "A 1971 circuit design that allowed television equipment to detect a specific color in a video signal, enabling the green-screen effects we see in modern weather forecasts and movies.",
  "what_it_does": "This patent describes an analog circuit designed to identify a precise color within a video feed. It works by taking color difference signals and multiplying them by sine and cosine values of a control voltage, which effectively maps the color space to a coordinate system. By using a series of amplifiers, summers, and AND gates, the circuit creates an output pulse only when the incoming video signal matches the specific color selected by the operator. This pulse acts as a switch, telling the broadcast equipment to replace that specific color with another image, which is the fundamental mechanism behind chroma keying.",
  "what_it_does_not_cover": [
    "Does not cover digital image processing or software-based color keying algorithms.",
    "Does not cover the actual display or projection of the background image.",
    "Does not cover methods for generating the original red, green, and blue color signals.",
    "Does not cover non-analog signal processing techniques."
  ],
  "filed": "1971-03-12",
  "granted": "1972-07-18",
  "expires": "1991-03-12",
  "status": "expired",
  "holder": "Philips Broadcast Equipment Corp",
  "holder_url": "https://patentbrief.org/company/philips-broadcast-equipment-corp",
  "inventors": [
    {
      "name": "Peter Boxman",
      "url": "https://patentbrief.org/inventor/peter-boxman"
    },
    {
      "name": "Frederik Johannes Van Roessel",
      "url": "https://patentbrief.org/inventor/frederik-johannes-van-roessel"
    }
  ],
  "times_cited": 17,
  "tags": [
    "consumer_electronics",
    "mechanical",
    "telecommunications"
  ],
  "abstract": "A circuit for generating an output pulse upon the occurrence of a selected color in color television signals features a matrix to form two chrominance difference signals. Four variable gain amplifiers multiply the difference signals by the sine and cosine of a control voltage which is a course color control. Two circuits each comprising a summer, inverter, and clamp circuit each add the outputs of two of the multiplied signals. An AND gate combines the output of the summer circuits and also is coupled to a variable bias supply, which is a fine color control. A delay line, a second AND gate, and a clipper and zero reference then shape the output pulse.",
  "url": "https://patentbrief.org/patent/us/3678182/chroma-key-green-screen",
  "markdown_url": "https://patentbrief.org/patent/us/3678182/chroma-key-green-screen/md",
  "google_patents_url": "https://patents.google.com/patent/US3678182",
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}