{"record":{"id":"f4eb150a167df5aa","repo":"Yalantis/uCrop","slug":"load-pnm-colormax-field-is-undefined-in-file","errorCode":null,"errorMessage":"load_pnm(): COLORMAX field is undefined in file '%s'.","messagePattern":"load_pnm\\(\\): COLORMAX field is undefined in file '(.+?)'\\.","errorType":"console","errorClass":null,"httpStatus":null,"severity":"warning","filePath":"ucrop/src/main/jni/CImg.h","lineNumber":57589,"sourceCode":"        if (!file) cimg::fclose(nfile);\n        throw CImgIOException(_cimg_instance\n                              \"load_pnm(): PNM header not found in file '%s'.\",\n                              cimg_instance,\n                              filename?filename:\"(FILE*)\");\n      }\n      while ((err=std::fscanf(nfile,\" %16383[^\\n]\",item.data()))!=EOF && (*item=='#' || !err)) std::fgetc(nfile);\n      if ((err=cimg_sscanf(item,\" %u %u %u %u\",&W,&H,&D,&colormax))<2) {\n        if (!file) cimg::fclose(nfile);\n        throw CImgIOException(_cimg_instance\n                              \"load_pnm(): WIDTH and HEIGHT fields undefined in file '%s'.\",\n                              cimg_instance,\n                              filename?filename:\"(FILE*)\");\n      }\n      if (ppm_type!=1 && ppm_type!=4) {\n        if (err==2 || (err==3 && (ppm_type==5 || ppm_type==7 || ppm_type==8 || ppm_type==9))) {\n          while ((err=std::fscanf(nfile,\" %16383[^\\n]\",item.data()))!=EOF && (*item=='#' || !err)) std::fgetc(nfile);\n          if (cimg_sscanf(item,\"%u\",&colormax)!=1)\n            cimg::warn(_cimg_instance\n                       \"load_pnm(): COLORMAX field is undefined in file '%s'.\",\n                       cimg_instance,\n                       filename?filename:\"(FILE*)\");\n        } else { colormax = D; D = 1; }\n      }\n      std::fgetc(nfile);\n\n      if (filename) { // Check that dimensions specified in file does not exceed the buffer dimension\n        const cimg_int64 siz = cimg::fsize(filename);\n        if (W*H*D>siz)\n          throw CImgIOException(_cimg_instance\n                                \"load_pnm(): Specified image dimensions in file '%s' exceed file size.\",\n                                cimg_instance,\n                                filename);\n      }\n\n      switch (ppm_type) {\n      case 1 : { // 2D B&W ascii","sourceCodeStart":57571,"sourceCodeEnd":57607,"githubUrl":"https://github.com/Yalantis/uCrop/blob/f788b534b48c144edf786c8cddbf0e029e637804/ucrop/src/main/jni/CImg.h#L57571-L57607","documentation":"CImg<T>::load_pnm() parses Netpbm (PBM/PGM/PPM) headers token by token. For types other than P1/P4 (plain/binary bitmap, which have no COLORMAX), it expects a third header field, the maximum gray/color value; if fscanf of that field fails (cimg_sscanf != 1), it warns non-fatally and continues with an undefined/zero colormax, which later corrupts scaling of pixel values.","triggerScenarios":"Loading a PGM/PPM (P2,P3,P5,P6...) file whose header lacks the COLORMAX field — e.g. only \"P2\\n640 480\\n\" then pixel data, or the field is replaced by a comment/garbage that sscanf('%u') cannot parse.","commonSituations":"Hand-written or generated PNM files missing the maxval line, files where a comment line is malformed and consumed incorrectly, third-party tools emitting non-conforming Netpbm headers.","solutions":["Fix the PNM file so its header contains the three required fields: magic, width height, and maxval (e.g. \"P5\\n640 480\\n255\\n\")","Ensure the maxval is a plain integer with no stray characters or misplaced comment lines between header tokens","Regenerate the file with a conforming Netpbm tool (pnmtoplainpnm, ImageMagick convert) to normalize the header","Add a pre-parse header check in your pipeline that validates the presence of the maxval line before calling load_pnm"],"exampleFix":"// before (broken header)\nP5\n640 480\n<raw data>          // missing maxval line\n// after\nP5\n640 480\n255\n<raw data>","handlingStrategy":"validation","validationCode":"// validate a PGM/PPM header has magic, dimensions, and maxval before load_pnm\nstd::ifstream in(path);\nstd::string magic; int w = 0, h = 0, maxval = 0;\nin >> magic >> w >> h >> maxval;\nif (!(magic == \"P2\" || magic == \"P3\" || magic == \"P5\" || magic == \"P6\") ||\n    w <= 0 || h <= 0 || maxval <= 0 || maxval > 65535)\n  throw std::runtime_error(\"malformed PNM header (missing/invalid COLORMAX)\");","typeGuard":"bool valid_pnm_header(const std::string& magic, int maxval) {\n  return (magic == \"P2\" || magic == \"P3\" || magic == \"P5\" || magic == \"P6\") && maxval > 0;\n}","tryCatchPattern":null,"preventionTips":["Ensure PNM files carry the maxval line (except P1/P4 which have none)","Regenerate headers with conforming Netpbm/ImageMagick tools","Keep comments out of the middle of PNM headers","Pre-parse the header in pipeline ingestion to fail fast"],"tags":["pnm","netpbm","image-loading","malformed-header","cimg"],"backgroundTag":"invalid-argument-format","analyzedSha":"f788b534b48c144edf786c8cddbf0e029e637804","analyzedAt":"2026-09-08T08:36:04.887Z","contentChangedAt":"2026-09-08T08:36:04.887Z","schemaVersion":2},"datasetVersion":"2026-09-14T05:17:10.506Z"}