{
    "mode": "man",
    "parameter": "pgmdeshadow",
    "section": "1",
    "url": "https://www.chedong.com/phpMan.php/man/pgmdeshadow/1/json",
    "generated": "2026-09-03T23:20:30Z",
    "synopsis": "",
    "sections": {
        "NAME": {
            "content": "pgmdeshadow - Deshadow a PGM image\n\n",
            "subsections": []
        },
        "SYNOPSIS": {
            "content": "",
            "subsections": [
                {
                    "name": "pgmdeshadow",
                    "content": "[pnmfile]\n\n"
                }
            ]
        },
        "DESCRIPTION": {
            "content": "This program is part of Netpbm(1).\n\npgmdeshadow removes gray shadows from an image.  This is useful for an image containing text,\nsuch  as  a scanned book pages, where a shadow typically appears near the book crease or near\none side of the image.  pgmdeshadow recognizes a gray shadow as an area of smoothly  changing\ncolor,  starting  from  the outer edges of the image.  The program uses a simple image recon‐\nstruction algorithm to determine the local shadow gray level, then divides each pixel's  gray\nlevel by the local shadow gray level.\n\nThe  algorithm  is the \"fast hybrid grayscale reruction\" algorithm from Luc Vincent, \"Morpho‐\nlogical Grayscale Reruction in Image Analysis: Applications and Efficient Algorithms.\n\n\n",
            "subsections": []
        },
        "OPTIONS": {
            "content": "There are no command line options defined specifically for pgmdeshadow, but it recognizes the\noptions common to all programs based on libnetpbm (See \u001b]8;;index.html#commonoptions\u001b\\ Common Options\u001b]8;;\u001b\\ .)\n\n",
            "subsections": []
        },
        "REFERENCES": {
            "content": "•      Luc Vincent, \"Morphological Grayscale Reconstruction in Image  Analysis:  Applications\nand Efficient Algorithms,\" IEEE Transactions on Image Processing, vol. 2, no. 2, April\n1993, pp. 176-201.\n\n\n\n\n",
            "subsections": []
        },
        "SEE ALSO": {
            "content": "ppmshadow(1), pgm(1)\n\n",
            "subsections": []
        },
        "HISTORY": {
            "content": "pgmdeshadow was added to Netpbm in Version 10.35 (August 2006).\n",
            "subsections": []
        },
        "DOCUMENT SOURCE": {
            "content": "This  manual  page  was  generated by the Netpbm tool 'makeman' from HTML source.  The master\ndocumentation is at\n\nhttp://netpbm.sourceforge.net/doc/pgmdeshadow.html\n\nnetpbm documentation                        06 July 2006                  Pgmdeshadow User Manual(1)",
            "subsections": []
        }
    },
    "summary": "pgmdeshadow - Deshadow a PGM image",
    "flags": [],
    "examples": [],
    "see_also": [
        {
            "name": "ppmshadow",
            "section": "1",
            "url": "https://www.chedong.com/phpMan.php/man/ppmshadow/1/json"
        },
        {
            "name": "pgm",
            "section": "1",
            "url": "https://www.chedong.com/phpMan.php/man/pgm/1/json"
        }
    ],
    "tldr": {
        "source": "official",
        "description": "Deshadow a PGM image.",
        "examples": [
            {
                "description": "Remove grey shadows from a PGM image",
                "command": "pgmdeshadow {{path/to/input_file.pgm}} > {{path/to/output_file.pgm}}"
            }
        ]
    }
}