save_jxl(): Instance has pixel values in [%g,%g], probable t

Error message

save_jxl(): Instance has pixel values in [%g,%g], probable type overflow in file '%s'.

What it means

This is a warning (via cimg::warn, not an exception) emitted by CImg<T>::save_jxl() when the image's pixel range does not fit the target JPEG XL bit depth. If any pixel is negative, or the range exceeds 255 for 8-bit or 65535 for 16-bit output, values will be clipped/wrap around during conversion to bytes_per_pixel-wide integers. The save continues; only data fidelity is at risk.

Source

Thrown at ucrop/src/main/jni/CImg.h:61775

    **/
    const CImg<T>& save_jxl(const char *const filename, const float distance=1.0f,
                            const unsigned int bytes_per_pixel=0) const {
      return _save_jxl(filename,distance,bytes_per_pixel);
    }

    const CImg<T>& _save_jxl(const char *const filename, const float distance=1.0f,
                             const unsigned int bytes_per_pixel=0) const {
      if (!filename)
        throw CImgArgumentException(_cimg_instance
                                    "save_jxl(): Specified filename is (null).",
                                    cimg_instance);
      if (_spectrum > 4)
        throw CImgArgumentException(_cimg_instance
                                    "save_jxl(): JPEG XL only supports at most 4 channels.",
                                    cimg_instance);
      double stmin, stmax = (double)max_min(stmin);
      if (stmin<0 || (bytes_per_pixel==1 && stmax>=256) || stmax>=65536)
        cimg::warn(_cimg_instance
                   "save_jxl(): Instance has pixel values in [%g,%g], probable type overflow in file '%s'.",
                   cimg_instance,
                   stmin,stmax,filename);
      if (bytes_per_pixel>2 || sizeof(T)<bytes_per_pixel)
        throw CImgArgumentException(_cimg_instance
                                    "save_jxl(): bytes_per_pixel must be in [0, 2] and less than or equal to sizeof(T)",
                                    cimg_instance);
      if (_depth>1)
        cimg::warn(_cimg_instance
                   "save_jxl(): Instance is volumetric, only the first slice will be saved in file '%s'.",
                   cimg_instance,
                   filename);
#ifndef cimg_use_jxl
      cimg::unused(distance);
      return save_other(filename);
#else
      std::FILE *file = cimg::fopen(filename, "wb");
      cimg_uint32 nChannels = _spectrum;

View on GitHub (pinned to f788b534b4)

Solutions

Clamp/normalize pixel values to [0,255] (or [0,65535] for bytes_per_pixel==2) before saving, e.g. img = img.get_cut(0,255) or img.normalize(0,255)
Increase bytes_per_pixel to 2 if values fit in 16 bits
Shift the data so stmin>=0 before saving
Ignore the warning if clipping is acceptable

Example fix

// before
img.save_jxl("out.jxl"); // values in [-12, 900]
// after
CImg<T> out = img.get_cut(0,255); // or get_normalize(0,255)
out.save_jxl("out.jxl");

Defensive patterns

Strategy: validation

Validate before calling

double mn, mx = img.max_min(mn);
if (mn < 0 || mx >= 256) img.normalize(0,255); // then save_jxl

Try / catch

// cimg::warn does not throw; check the saved range before writing:
double mn, mx = img.max_min(mn);
assert(mn >= 0 && mx < 256);

Prevention

Always normalize or cut values to the target bit depth before saving
Check img.min()/img.max() before encode
Prefer float-capable formats for non-byte data

When it happens

Trigger: Calling save_jxl() with bytes_per_pixel==1 while pixel max >= 256, or bytes_per_pixel==2 while pixel max >= 65536, or with any negative pixel value (stmin<0), as computed by max_min() just before the check.

Common situations: Saving float or int32 images whose values exceed 0-255 (e.g. HDR data, raw sensor values, scientific imagery) to 8-bit JXL; images containing negative values from filters, derivatives, or signed processing pipelines.

Understand the failure class

Background: "value must be between 0 and 1" / "out of range" / "must not be negative" errors: fixing range-validation failures across open-source libraries — this error's family across 42 libraries.

Related errors

AI-assisted analysis of Yalantis/uCrop@f788b534b4 (2026-09-08). Data as JSON: /api/errors/20198e59c78950db. Report an issue: GitHub.