Yalantis/uCrop · warning

load_pnm(): COLORMAX field is undefined in file '%s'.

Error message

load_pnm(): COLORMAX field is undefined in file '%s'.

What it means

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.

Source

Thrown at ucrop/src/main/jni/CImg.h:57589

        if (!file) cimg::fclose(nfile);
        throw CImgIOException(_cimg_instance
                              "load_pnm(): PNM header not found in file '%s'.",
                              cimg_instance,
                              filename?filename:"(FILE*)");
      }
      while ((err=std::fscanf(nfile," %16383[^\n]",item.data()))!=EOF && (*item=='#' || !err)) std::fgetc(nfile);
      if ((err=cimg_sscanf(item," %u %u %u %u",&W,&H,&D,&colormax))<2) {
        if (!file) cimg::fclose(nfile);
        throw CImgIOException(_cimg_instance
                              "load_pnm(): WIDTH and HEIGHT fields undefined in file '%s'.",
                              cimg_instance,
                              filename?filename:"(FILE*)");
      }
      if (ppm_type!=1 && ppm_type!=4) {
        if (err==2 || (err==3 && (ppm_type==5 || ppm_type==7 || ppm_type==8 || ppm_type==9))) {
          while ((err=std::fscanf(nfile," %16383[^\n]",item.data()))!=EOF && (*item=='#' || !err)) std::fgetc(nfile);
          if (cimg_sscanf(item,"%u",&colormax)!=1)
            cimg::warn(_cimg_instance
                       "load_pnm(): COLORMAX field is undefined in file '%s'.",
                       cimg_instance,
                       filename?filename:"(FILE*)");
        } else { colormax = D; D = 1; }
      }
      std::fgetc(nfile);

      if (filename) { // Check that dimensions specified in file does not exceed the buffer dimension
        const cimg_int64 siz = cimg::fsize(filename);
        if (W*H*D>siz)
          throw CImgIOException(_cimg_instance
                                "load_pnm(): Specified image dimensions in file '%s' exceed file size.",
                                cimg_instance,
                                filename);
      }

      switch (ppm_type) {
      case 1 : { // 2D B&W ascii

View on GitHub (pinned to f788b534b4)

Solutions

1. Fix the PNM file so its header contains the three required fields: magic, width height, and maxval (e.g. "P5\n640 480\n255\n")
2. Ensure the maxval is a plain integer with no stray characters or misplaced comment lines between header tokens
3. Regenerate the file with a conforming Netpbm tool (pnmtoplainpnm, ImageMagick convert) to normalize the header
4. Add a pre-parse header check in your pipeline that validates the presence of the maxval line before calling load_pnm

Example fix

// before (broken header)
P5
640 480
<raw data>          // missing maxval line
// after
P5
640 480
255
<raw data>

// validate a PGM/PPM header has magic, dimensions, and maxval before load_pnm
std::ifstream in(path);
std::string magic; int w = 0, h = 0, maxval = 0;
in >> magic >> w >> h >> maxval;
if (!(magic == "P2" || magic == "P3" || magic == "P5" || magic == "P6") ||
    w <= 0 || h <= 0 || maxval <= 0 || maxval > 65535)
  throw std::runtime_error("malformed PNM header (missing/invalid COLORMAX)");

bool valid_pnm_header(const std::string& magic, int maxval) {
  return (magic == "P2" || magic == "P3" || magic == "P5" || magic == "P6") && maxval > 0;
}

When it happens

Trigger: 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.

Common situations: 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.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

• load_pnm(): WIDTH and HEIGHT fields undefined in file '%s'.
• load_pnm(): PNM header not found in file '%s'.
• load_pnm(): Specified image dimensions in file '%s' exceed f
• load_pnm(): PNM type 'P%d' found, but type is not supported.
• load_pfm(): PFM header not found in file '%s'.

AI-assisted analysis of Yalantis/uCrop@f788b534b4 (2026-09-08). Data as JSON: /api/errors/f4eb150a167df5aa. Report an issue: GitHub.