Why would C++ compiler assume parameters are being passed by reference

I have a class PixelVector whose constructor signature looks like:

PixelVector(unsigned int r=0, unsigned int c=0, unsigned int max=255);

In another Image class I have a private variable, PixelVector pixels. I initialize it with:

pixels(height,width,readMax);

where all the parameters have the correct type and are guaranteed to be already initialized.

I want to pass these by value but when I compile I get the error:

image.cpp:185:30: error: no match for call to ‘(PixelVector) (unsigned int&, unsigned int&, unsigned int&)’

Why is the compiler thinking I'm passing the values by reference. How do I force it to pass by value?