Yalantis/uCrop · error · CImgInstanceException

_cimg_instance "minabs(): Empty instance."

Error message

_cimg_instance "minabs(): Empty instance."

What it means

CImg<T>::minabs() returns a reference to the pixel with the smallest absolute value; on an empty instance there is no pixel to inspect, so CImgInstanceException is thrown instead of dereferencing invalid memory.

Solutions

  1. Check img.is_empty() before calling minabs()
  2. Fix the step that produced the empty image (load path, ROI bounds)

Example fix

// before
float v = img.minabs();
// after
if (!img.is_empty()) { float v = img.minabs(); }
Defensive patterns

Strategy: validation

Validate before calling

if (!img.is_empty()) { ... img.minabs() ... }

Try / catch

try { T v = img.minabs(); } catch (const CImgInstanceException& e) { /* handle empty */ }

Prevention

When it happens

Trigger: Calling img.minabs() on a zero-size CImg (default-constructed, cleared, or produced by an empty crop/load).

Common situations: Signal/statistics code assuming the input was loaded; pipelines where a previous threshold or channel extraction emptied the buffer.

Understand the failure class

Background: EmptyResultError / "no results found": when an API or scraper succeeds but returns zero rows — this error's family across 9 libraries.

Related errors

AI-assisted analysis of Yalantis/uCrop@f788b534b4 (2026-09-08). Data as JSON: /api/errors/cea41ba72d72bc03. Report an issue: GitHub.

Appendix: source

Thrown at ucrop/src/main/jni/CImg.h:31775

    //! Return a reference to the minimum pixel value \const.
    const T& min() const {
      if (is_empty())
        throw CImgInstanceException(_cimg_instance
                                    "min(): Empty instance.",
                                    cimg_instance);
      const T *ptr_min = _data;
      T min_value = *ptr_min;
      cimg_for(*this,ptrs,T) if (*ptrs<min_value) min_value = *(ptr_min=ptrs);
      return *ptr_min;
    }

    //! Return a reference to the minimum pixel value in absolute value.
    /**
     **/
    T& minabs() {
      if (is_empty())
        throw CImgInstanceException(_cimg_instance
                                    "minabs(): Empty instance.",
                                    cimg_instance);
      T *ptr_minabs = _data;
      T minabs_value = *ptr_minabs;
      cimg_for(*this,ptrs,T) {
        const T ma = cimg::abs(*ptrs);
        if (ma<minabs_value) { minabs_value = ma; ptr_minabs = ptrs; }
      }
      return *ptr_minabs;
    }

    //! Return a reference to the minimum pixel value in absolute value \const.
    const T& minabs() const {
      if (is_empty())
        throw CImgInstanceException(_cimg_instance
                                    "minabs(): Empty instance.",
                                    cimg_instance);
      const T *ptr_minabs = _data;

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