Yalantis/uCrop · error · CImgInstanceException

xyYtoXYZ(): Instance is not a xyY image.

Error message

xyYtoXYZ(): Instance is not a xyY image.

What it means

xyYtoXYZ() converts xyY chromaticity values back to CIE XYZ and requires exactly 3 channels (x, y, Y). It throws CImgInstanceException when _spectrum != 3, since the transform indexes three channel planes. This is the inverse of XYZtoxyY and is only valid on images in xyY layout.

Source

Thrown at ucrop/src/main/jni/CImg.h:37695

          Z = (Tfloat)p3[N],
          sum = X + Y + Z,
          nsum = sum>0?sum:1;
        p1[N] = (T)(X/nsum);
        p2[N] = (T)(Y/nsum);
        p3[N] = (T)Y;
      }
      return *this;
    }

    //! Convert pixel values from XYZ to xyY color spaces \newinstance.
    CImg<Tfloat> get_XYZtoxyY() const {
      return CImg<Tfloat>(*this,false).XYZtoxyY();
    }

    //! Convert pixel values from xyY pixels to XYZ color spaces.
    CImg<T>& xyYtoXYZ() {
      if (_spectrum!=3)
        throw CImgInstanceException(_cimg_instance
                                    "xyYtoXYZ(): Instance is not a xyY image.",
                                    cimg_instance);

      T *p1 = data(0,0,0,0), *p2 = data(0,0,0,1), *p3 = data(0,0,0,2);
      const longT whd = (longT)width()*height()*depth();
      cimg_pragma_openmp(parallel for cimg_openmp_if_size(whd,4096))
      for (longT N = 0; N<whd; ++N) {
        const Tfloat
         px = (Tfloat)p1[N],
         py = (Tfloat)p2[N],
         Y = (Tfloat)p3[N],
         ny = py>0?py:1;
        p1[N] = (T)(px*Y/ny);
        p2[N] = (T)Y;
        p3[N] = (T)((1 - px - py)*Y/ny);
      }
      return *this;
    }

View on GitHub (pinned to f788b534b4)

Solutions

1. Check img.spectrum()==3 before the call and fix the pipeline so xyY data is stored as exactly 3 channels.
2. Only call xyYtoXYZ on the result of XYZtoxyY(); for raw RGB use RGBtoXYZ() instead.
3. Remove or separate extra channels: get_channels(0,2) for RGBA, or duplicate gray channels for 1-channel images.
4. Wrap the call in try/catch for CImgInstanceException in native code.

Example fix

// before
img.xyYtoXYZ(); // img is grayscale, spectrum==1 -> throws
// after
if (img.spectrum()==1) img = img.get_resize(img.width(),img.height(),1,3); // replicate to 3 channels after ensuring data is xyY
img.xyYtoXYZ();

if (img.spectrum()!=3) { /* repair before xyYtoXYZ */ }

template<class T> bool has3Channels(const cimg_library::CImg<T>& i){ return i.spectrum()==3; }

try { img.xyYtoXYZ(); } catch (cimg_library::CImgInstanceException& e) { /* recover */ }

When it happens

Trigger: Calling img.xyYtoXYZ() on an image with spectrum != 3 — grayscale images, RGB/RGBA images not in xyY form, or images where the alpha channel makes the count 4.

Common situations: Reversing a chromaticity conversion on an image that still carries an alpha channel; applying xyYtoXYZ to raw RGB data (never converted to xyY); loading multi-channel spectral data and forgetting to reduce to 3 channels.

Understand the failure class

Background: "is not a compatible type" / "cannot merge" errors: when a value's type doesn't match what the library requires — this error's family across 65 libraries.

Related errors

• XYZtoLab(): Instance is not a XYZ image.
• LabtoXYZ(): Instance is not a Lab image.
• XYZtoxyY(): Instance is not a XYZ image.
• RGBtoYCbCr(): Instance is not a RGB image.
• YCbCrtoRGB(): Instance is not a YCbCr image.

AI-assisted analysis of Yalantis/uCrop@f788b534b4 (2026-09-08). Data as JSON: /api/errors/1d5ba0b35251e7ce. Report an issue: GitHub.