"picture black" meaning in English

{
  "forms": [
    {
      "form": "picture blacks",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "~"
      },
      "expansion": "picture black (countable and uncountable, plural picture blacks)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Television",
          "orig": "en:Television",
          "parents": [
            "Broadcasting",
            "Mass media",
            "Media",
            "Telecommunications",
            "Culture",
            "Communication",
            "Technology",
            "Society",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "examples": [
        {
          "ref": "1966, Rodger J. Ross, Television Film Engineering, page 331",
          "text": "At the same time the picture blacks may be reproduced at levels as high as 20 or 30 IRE units.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "The darkest black that can be produced in a television image."
      ],
      "id": "en-picture_black-en-noun-ba1qgTL5",
      "links": [
        [
          "television",
          "television"
        ]
      ],
      "raw_glosses": [
        "(television) The darkest black that can be produced in a television image."
      ],
      "tags": [
        "countable",
        "uncountable"
      ],
      "topics": [
        "broadcasting",
        "media",
        "television"
      ]
    }
  ],
  "word": "picture black"
}

{
  "forms": [
    {
      "form": "picture blacks",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "~"
      },
      "expansion": "picture black (countable and uncountable, plural picture blacks)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English terms with quotations",
        "English uncountable nouns",
        "Quotation templates to be cleaned",
        "en:Television"
      ],
      "examples": [
        {
          "ref": "1966, Rodger J. Ross, Television Film Engineering, page 331",
          "text": "At the same time the picture blacks may be reproduced at levels as high as 20 or 30 IRE units.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "The darkest black that can be produced in a television image."
      ],
      "links": [
        [
          "television",
          "television"
        ]
      ],
      "raw_glosses": [
        "(television) The darkest black that can be produced in a television image."
      ],
      "tags": [
        "countable",
        "uncountable"
      ],
      "topics": [
        "broadcasting",
        "media",
        "television"
      ]
    }
  ],
  "word": "picture black"
}