Yalantis/uCrop · error · CImgArgumentException

draw_graph(): Specified color is (null).

Error message

draw_graph(): Specified color is (null).

What it means

draw_graph() plots a 1D data series inside the image and requires a non-null color pointer, throwing CImgArgumentException when color is null. The color buffer must supply at least spectrum() channel values used for the plot line/bars; the routine also derives shaded variants (color1/color2) from it for bar plots, which is impossible with a null base color.

Source

Thrown at ucrop/src/main/jni/CImg.h:53404

                      - 3 = Diagonal cross.
                      - 4 = Filled circle.
                      - 5 = Outlined circle.
                      - 6 = Square.
                      - 7 = Diamond.
       \param ymin Lower bound of the y-range.
       \param ymax Upper bound of the y-range.
       \param pattern Drawing pattern.
       \note
         - if \c ymin==ymax==0, the y-range is computed automatically from the input samples.
    **/
    template<typename t, typename tc>
    CImg<T>& draw_graph(const CImg<t>& data,
                        const tc *const color, const float opacity=1,
                        const unsigned int plot_type=1, const int vertex_type=1,
                        const double ymin=0, const double ymax=0, const unsigned int pattern=~0U) {
      if (is_empty() || _height<=1) return *this;
      if (!color)
        throw CImgArgumentException(_cimg_instance
                                    "draw_graph(): Specified color is (null).",
                                    cimg_instance);

      // Create shaded colors for displaying bar plots.
      CImg<tc> color1, color2;
      if (plot_type==3) {
        color1.assign(_spectrum); color2.assign(_spectrum);
        cimg_forC(*this,c) {
          color1[c] = (tc)std::min((float)cimg::type<tc>::max(),(float)color[c]*1.2f);
          color2[c] = (tc)(color[c]*0.4f);
        }
      }

      // Compute min/max and normalization factors.
      const ulongT
        siz = data.size(),
        _siz1 = siz - (plot_type!=3),
        siz1 = _siz1?_siz1:1;

View on GitHub (pinned to f788b534b4)

Solutions

1. Pass a valid color array with spectrum() elements, e.g. const unsigned char col[]={200,30,30}.
2. Null-check and substitute a default color before the call.
3. Guard optional-color higher-level APIs so they materialize a concrete color rather than forwarding null.
4. In bindings, validate non-null color arrays at the boundary.

Example fix

// before
img.draw_graph(profile,getColorOpt(),1,1,1);
// after
const unsigned char* c = getColorOpt();
if (!c) { static const unsigned char def[3]={255,255,0}; c=def; }
img.draw_graph(profile,c,1,1,1);

if (!color) color = defaultPlotColor;
img.draw_graph(data,color,opacity,plot_type,vertex_type);

template<typename T> bool hasPlotColor(const T* c){ return c != nullptr; }

try { img.draw_graph(data,color); }
catch (CImgArgumentException& e) { log_error("draw_graph: %s", e.what()); }

When it happens

Trigger: img.draw_graph(data,NULL) or passing a color pointer that was never allocated/freed; optional color parameters threaded through from an outer API that defaulted to null; wrapper bindings forwarding null arrays.

Common situations: Palette lookup failure returning null; refactored signatures where the color argument shifted position; JNI/managed bindings passing null byte[] for the plot color.

Related errors

• draw_rectangle(): Specified color is (null).
• draw_polygon(): Specified color is (null).
• draw_ellipse(): Specified color is (null).
• draw_circle(): Specified color is (null).
• draw_gaussian(): Specified color is (null).

AI-assisted analysis of Yalantis/uCrop@f788b534b4 (2026-09-08). Data as JSON: /api/errors/a3382a87efa541bf. Report an issue: GitHub.