Call of overloaded is ambiguous

I have the following compiler error : `"call of overloaded ‘reduceColors(ipl_image_wrapper&, ipl_image_wrapper&, int)’ is ambiguous"` I have a wrapper class for IplImage (DrawingDetection.h): ``` #include <opencv2/opencv.hpp> #include <opencv2/imgproc/imgproc.hpp> #include <opencv2/objdetect/objdetect.hpp> #include <opencv2/features2d/features2d.hpp> #include <boost/shared_ptr.hpp> #include "Utils.h" class ipl_image_wrapper { public: typedef boost::shared_ptr< IplImage > ipl_image_ptr_t; ipl_image_wrapper() {} ipl_image_wrapper( IplImage* img ) : _img( img, ipl_deleter ) {} IplImage* get() { return _img.get(); } const IplImage* get() const { return _img.get(); } private: static void ipl_deleter( IplImage* ipl_img ) { //some code } ipl_image_ptr_t _img; }; ``` And I have the following functions (Utils.h): ``` #include "DrawingDetection.h" int calculateHomogeneity(const ipl_image_wrapper &img, Factor & factor); void reduceColors(const ipl_image_wrapper &img, ipl_image_wrapper &out, int levels); int calculateCComponentsSize(const ipl_image_wrapper &img, Factor &factor); ``` There is no other declarations of this functions (!). I'm not overloading them. And source code with error (Utils.cpp): ``` #include <boost/shared_ptr.hpp> #include "Utils.h" int calculateCComponentsSize(const ipl_image_wrapper img, Factor &factor) { // some calculations } void reduceColors(const ipl_image_wrapper &img, ipl_image_wrapper out, int levels) { // some calculations } int calculateHomogeneity(const ipl_image_wrapper &img, Factor & factor) { // some calculations } void getFactorsOfImage( const ipl_image_wrapper &image, Factor& factor ) { ipl_image_wrapper gray = cvCreateImage( cvGetSize ( image.get() ), IPL_DEPTH_8U, 1); // some calculations calculateHomogeneity( gray, factor ); // ok reduceColors( gray, gray, 20 ); // ambiguity !! int n1 = calculateCComponentsSize( gray, factor );// ambiguity !! reduceColors( gray, gray, 8 );// ambiguity !! int n2 = calculateCComponentsSize( gray, factor );// ambiguity !! // some calculations } ``` What is the diiference between calculateHomogeneity(...) function and the rest? They have a similar list of parameters. Where the compiler found the ambiguity? EDIT: Declaration order of function has been very important. Source code without error (Utils.cpp): ``` #include <boost/shared_ptr.hpp> #include "Utils.h" void getFactorsOfImage( const ipl_image_wrapper &image, Factor& factor ) { ipl_image_wrapper gray = cvCreateImage( cvGetSize ( image.get() ), IPL_DEPTH_8U, 1); // some calculations calculateHomogeneity( gray, factor ); // ok reduceColors( gray, gray, 20 ); // ambiguity !! int n1 = calculateCComponentsSize( gray, factor );// ambiguity !! reduceColors( gray, gray, 8 );// ambiguity !! int n2 = calculateCComponentsSize( gray, factor );// ambiguity !! // some calculations } // After getFactorsOfImage function int calculateCComponentsSize(const ipl_image_wrapper img, Factor &factor) { // some calculations } void reduceColors(const ipl_image_wrapper &img, ipl_image_wrapper out, int levels) { // some calculations } int calculateHomogeneity(const ipl_image_wrapper &img, Factor & factor) { // some calculations } ```