Yalantis/uCrop · error · CImgArgumentException

display(): Empty specified image.

Error message

display(): Empty specified image.

What it means

CImgDisplay::display(const CImg<T>&) throws CImgArgumentException when the image passed to it is empty (operator bool() is false because _width/_height are 0). The display cannot render a zero-sized image, so the library refuses early instead of rendering nothing. It is a caller-supplied argument problem, not a display or window problem.

Solutions

1. Check the image with if (img) before calling display().
2. Fix the code path that produces the empty image (failed load, bad file, zero-sized crop) so a valid image reaches display().
3. If an empty display is legitimate, call is_empty()/assign() on the CImgDisplay instead of displaying an empty image.

Example fix

// before
CImg<unsigned char> img; // never filled
disp.display(img); // throws
// after
CImg<unsigned char> img("input.png");
if (img) disp.display(img);

if (!img) { /* image is empty: width or height is 0 */ return; }
disp.display(img);

bool nonEmpty(const cimg_library::CImg<T>& img) { return (bool)img; } // true iff _width>0 && _height>0

try { disp.display(img); }
catch (cimg_library::CImgArgumentException &e) { fprintf(stderr, "%s", e.what()); }

When it happens

Trigger: Calling display(img) where img was default-constructed, assign()-reset, constructed with a 0 dimension, or where a previous load/assign operation silently failed and left the image empty.

Common situations: Loading a corrupted or missing image file and passing the result straight to display(); guarding code that checks only the pointer and not the image dimensions; reusing an image object after assign() without re-loading.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

• render(): Empty specified image.
• at(): Empty instance.
• atX(): Empty instance.
• atXY(): Empty instance.
• atXYZ(): Empty instance.

AI-assisted analysis of Yalantis/uCrop@f788b534b4 (2026-09-08). Data as JSON: /api/errors/8968b34621846b97. Report an issue: GitHub.

Appendix: source

Thrown at ucrop/src/main/jni/CImg.h:12505

      return *this;
    }

    CImgDisplay& set_mouse(const int posx, const int posy) {
      if (is_empty() || _is_closed || posx<0 || posy<0) return *this;
      if (!_is_closed) {
        cimg::SDL3_attr &SDL3_attr = cimg::SDL3_attr::ref();
        SDL3_attr.lock();
        SDL_WarpMouseInWindow(_window,(float)posx,(float)posy);
        _mouse_x = posx; _mouse_y = posy;
        SDL3_attr.unlock();
      }
      return *this;
    }

    template<typename T>
    CImgDisplay& display(const CImg<T>& img) {
      if (!img)
        throw CImgArgumentException(_cimgdisplay_instance
                                    "display(): Empty specified image.",
                                    cimgdisplay_instance);
      if (is_empty()) return assign(img);
      return render(img).paint();
    }

    CImgDisplay& paint() {
      if (_is_closed) return *this;
      cimg::SDL3_attr &SDL3_attr = cimg::SDL3_attr::ref();

      const SDL_ThreadID current_thread_id = SDL_GetCurrentThreadID();
      if (current_thread_id!=_thread_id) {
        // Make sure repaint is done by the thread that created the window.
        _paint_request = true;
        return *this;
      }

      SDL3_attr.lock();

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