{ "content": [ { "type": "text", "text": "# pgm(5) (man)\n\n**Summary:** pgm - portable graymap file format\n\n## See Also\n\n- fitstopgm(1)\n- fstopgm(1)\n- hipstopgm(1)\n- lispmtopgm(1)\n- psidtopgm(1)\n- rawtopgm(1)\n- ley(1)\n- pgmcrater(1)\n- pgmedge(1)\n- pgmenhance(1)\n- pgmhist(1)\n- pgmnorm(1)\n- pgmoil(1)\n- ramp(1)\n- pgmtexture(1)\n- pgmtofits(1)\n- pgmtofs(1)\n- pgmtolispm(1)\n- pgmtopbm(1)\n- pnm(5)\n- pbm(5)\n- ppm(5)\n\n## Section Outline\n\n- **NAME** (3 lines)\n- **DESCRIPTION** (102 lines)\n- **COMPATIBILITY** (7 lines)\n- **SEE ALSO** (5 lines)\n- **AUTHOR** (5 lines)\n\n## Full Content\n\n### NAME\n\npgm - portable graymap file format\n\n### DESCRIPTION\n\nThe PGM format is a lowest common denominator grayscale file format. It is designed to be\nextremely easy to learn and write programs for. (It's so simple that most people will simply\nreverse engineer it because it's easier than reading this specification).\n\nA PGM image represents a grayscale graphic image. There are many psueudo-PGM formats in use\nwhere everything is as specified herein except for the meaning of individual pixel values.\nFor most purposes, a PGM image can just be thought of an array of arbitrary integers, and all\nthe programs in the world that think they're processing a grayscale image can easily be\ntricked into processing something else.\n\nOne official variant of PGM is the transparency mask. A transparency mask in Netpbm is rep‐\nresented by a PGM image, except that in place of pixel intensities, there are opaqueness val‐\nues. See below.\n\n\nThe format definition is as follows.\n\nA PGM file consists of a sequence of one or more PGM images. There are no data, delimiters,\nor padding before, after, or between images.\n\nEach PGM image consists of the following:\n\n- A \"magic number\" for identifying the file type. A pgm image's magic number is the two\ncharacters \"P5\".\n\n- Whitespace (blanks, TABs, CRs, LFs).\n\n- A width, formatted as ASCII characters in decimal.\n\n- Whitespace.\n\n- A height, again in ASCII decimal.\n\n- Whitespace.\n\n- The maximum gray value (Maxval), again in ASCII decimal. Must be less than 65536.\n\n- Newline or other single whitespace character.\n\n- A raster of Width * Height gray values, proceeding through the image in normal English\nreading order. Each gray value is a number from 0 through Maxval, with 0 being black and\nMaxval being white. Each gray value is represented in pure binary by either 1 or 2 bytes.\nIf the Maxval is less than 256, it is 1 byte. Otherwise, it is 2 bytes. The most signifi‐\ncant byte is first.\n\n- Each gray value is a number proportional to the intensity of the pixel, adjusted by the CIE\nRec. 709 gamma transfer function. (That transfer function specifies a gamma number of 2.2\nand has a linear section for small intensities). A value of zero is therefore black. A\nvalue of Maxval represents CIE D65 white and the most intense value in the image and any\nother image to which the image might be compared.\n\n- Note that a common variation on the PGM format is to have the gray value be \"linear,\" i.e.\nas specified above except without the gamma adjustment. pnmgamma takes such a PGM variant\nas input and produces a true PGM as output.\n\n- In the transparency mask variation on PGM, the value represents opaqueness. It is propor‐\ntional to the fraction of intensity of a pixel that would show in place of an underlying\npixel, with the same gamma transfer function mentioned above applied. So what normally\nmeans white represents total opaqueness and what normally means black represents total\ntransparency. In between, you would compute the intensity of a composite pixel of an \"un‐\nder\" and \"over\" pixel as under * (1-(alpha/alphamaxval)) + over * (alpha/alphamaxval).<\n\n- Characters from a \"#\" to the next end-of-line, before the maxval line, are comments and are\nignored.\n\nNote that you can use pnmdepth To convert between a the format with 1 byte per gray value and\nthe one with 2 bytes per gray value.\n\nThere is actually another version of the PGM format that is fairly rare: \"plain\" PGM format.\nThe format above, which generally considered the normal one, is known as the \"raw\" PGM for‐\nmat. See pbm(5) for some commentary on how plain and raw formats relate to one another.\n\nThe difference in the plain format is:\n\n- There is exactly one image in a file.\n\n- The magic number is P2 instead of P5.\n\n- Each pixel in the raster is represented as an ASCII decimal number (of arbitrary size).\n\n- Each pixel in the raster has white space before and after it. There must be at least one\ncharacter of white space between any two pixels, but there is no maximum.\n\n- No line should be longer than 70 characters.\n\nHere is an example of a small graymap in this format:\nP2\n# feep.pgm\n24 7\n15\n0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0\n0 3 3 3 3 0 0 7 7 7 7 0 0 11 11 11 11 0 0 15 15 15 15 0\n0 3 0 0 0 0 0 7 0 0 0 0 0 11 0 0 0 0 0 15 0 0 15 0\n0 3 3 3 0 0 0 7 7 7 0 0 0 11 11 11 0 0 0 15 15 15 15 0\n0 3 0 0 0 0 0 7 0 0 0 0 0 11 0 0 0 0 0 15 0 0 0 0\n0 3 0 0 0 0 0 7 7 7 7 0 0 11 11 11 11 0 0 15 0 0 0 0\n0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0\n\nPrograms that read this format should be as lenient as possible, accepting anything that\nlooks remotely like a graymap.\n\n### COMPATIBILITY\n\nBefore April 2000, a raw format PGM file could not have a maxval greater than 255. Hence, it\ncould not have more than one byte per sample. Old programs may depend on this.\n\nBefore July 2000, there could be at most one image in a PGM file. As a result, most tools to\nprocess PGM files ignore (and don't read) any data after the first image.\n\n### SEE ALSO\n\nfitstopgm(1), fstopgm(1), hipstopgm(1), lispmtopgm(1), psidtopgm(1), rawtopgm(1), pgmbent‐\nley(1), pgmcrater(1), pgmedge(1), pgmenhance(1), pgmhist(1), pgmnorm(1), pgmoil(1), pgm‐\nramp(1), pgmtexture(1), pgmtofits(1), pgmtofs(1), pgmtolispm(1), pgmtopbm(1), pnm(5), pbm(5),\nppm(5)\n\n### AUTHOR\n\nCopyright (C) 1989, 1991 by Jef Poskanzer.\n\n\n\n12 November 1991 pgm(5)\n\n" } ], "structuredContent": { "command": "pgm", "section": "5", "mode": "man", "summary": "pgm - portable graymap file format", "synopsis": null, "tldr_summary": null, "tldr_examples": [], "tldr_source": null, "flags": [], "examples": [], "see_also": [ { "name": "fitstopgm", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/fitstopgm/1/json" }, { "name": "fstopgm", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/fstopgm/1/json" }, { "name": "hipstopgm", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/hipstopgm/1/json" }, { "name": "lispmtopgm", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/lispmtopgm/1/json" }, { "name": "psidtopgm", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/psidtopgm/1/json" }, { "name": "rawtopgm", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/rawtopgm/1/json" }, { "name": "ley", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/ley/1/json" }, { "name": "pgmcrater", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/pgmcrater/1/json" }, { "name": "pgmedge", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/pgmedge/1/json" }, { "name": "pgmenhance", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/pgmenhance/1/json" }, { "name": "pgmhist", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/pgmhist/1/json" }, { "name": "pgmnorm", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/pgmnorm/1/json" }, { "name": "pgmoil", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/pgmoil/1/json" }, { "name": "ramp", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/ramp/1/json" }, { "name": "pgmtexture", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/pgmtexture/1/json" }, { "name": "pgmtofits", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/pgmtofits/1/json" }, { "name": "pgmtofs", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/pgmtofs/1/json" }, { "name": "pgmtolispm", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/pgmtolispm/1/json" }, { "name": "pgmtopbm", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/pgmtopbm/1/json" }, { "name": "pnm", "section": "5", "url": "https://www.chedong.com/phpMan.php/man/pnm/5/json" }, { "name": "pbm", "section": "5", "url": "https://www.chedong.com/phpMan.php/man/pbm/5/json" }, { "name": "ppm", "section": "5", "url": "https://www.chedong.com/phpMan.php/man/ppm/5/json" } ], "section_outline": [ { "name": "NAME", "lines": 3, "subsections": [] }, { "name": "DESCRIPTION", "lines": 102, "subsections": [] }, { "name": "COMPATIBILITY", "lines": 7, "subsections": [] }, { "name": "SEE ALSO", "lines": 5, "subsections": [] }, { "name": "AUTHOR", "lines": 5, "subsections": [] } ] } }