Yalantis/uCrop · error · CImgInstanceException

_cimg_instance "min_max(): Empty instance."

Error message

_cimg_instance "min_max(): Empty instance."

What it means

Instance guard in CImg<T>::min_max(t&): computing both minimum and maximum requires at least one pixel; the image is empty, so neither value exists. Same sentinel check used throughout the statistics methods.

Solutions

1. Check is_empty() / size()>0 before calling min_max()
2. Confirm the image load or data assignment succeeded
3. Fix zero-size ROI/crop inputs
4. Catch CImgInstanceException if the empty case must be tolerated

Example fix

// before
T maxv;
const T& minv = img.min_max(maxv);
// after
if (!img.is_empty()) {
  T maxv;
  const T& minv = img.min_max(maxv);
}

if (img.is_empty()) throw std::runtime_error("image empty before min_max()");

bool usable = !img.is_empty() && img.size() > 0;

try { T maxv; const T& minv = img.min_max(maxv); } catch (const CImgInstanceException& e) { /* handle empty */ }

When it happens

Trigger: Calling CImg<T>::min_max(t& max_val) on an instance where is_empty() is true — no pixels allocated or dimensions set to zero.

Common situations: Normalizing or rescaling an image that failed to load; computing min/max for auto-contrast on an empty buffer; passing a default-constructed CImg into a statistics routine.

Related errors

• _cimg_instance "kth_smallest(): Empty instance."
• _cimg_instance "max_min(): Empty instance."
• _cimg_instance "maxabs(): Empty instance."
• _cimg_instance "median(): Empty instance."
• _cimg_instance "variance_mean(): Empty instance."

AI-assisted analysis of Yalantis/uCrop@f788b534b4 (2026-09-08). Data as JSON: /api/errors/403013530795b405. Report an issue: GitHub.

Appendix: source

Thrown at ucrop/src/main/jni/CImg.h:31867

                                    "maxabs(): Empty instance.",
                                    cimg_instance);
      const T *ptr_maxabs = _data;
      T maxabs_value = *ptr_maxabs;
      cimg_for(*this,ptrs,T) {
        const T ma = cimg::abs(*ptrs);
        if (ma>maxabs_value) { maxabs_value = ma; ptr_maxabs = ptrs; }
      }
      return *ptr_maxabs;
    }

    //! Return a reference to the minimum pixel value as well as the maximum pixel value.
    /**
       \param[out] max_val Maximum pixel value.
    **/
    template<typename t>
    T& min_max(t& max_val) {
      if (is_empty())
        throw CImgInstanceException(_cimg_instance
                                    "min_max(): Empty instance.",
                                    cimg_instance);
      const T *ptr_min, *ptr_max;
      _min_max(ptr_min,ptr_max);
      max_val = (t)*ptr_max;
      return (T&)*ptr_min;
    }

    void _min_max(const T* &ptr_min, const T* &ptr_max) const {
      T val_min = *_data, val_max = val_min;
      ptr_min = ptr_max = _data;
      if (cimg_use_openmp && size()>(1LU<<24)*cimg_openmp_sizefactor) {
#if cimg_use_openmp
        cimg_pragma_openmp(parallel) {
          T l_val_min = *_data, l_val_max = l_val_min;
          const T *l_ptr_min = _data, *l_ptr_max = l_ptr_min;
          cimg_pragma_openmp(for)
          cimg_rofoff(*this,off) {

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