fixed #1565 issue

modules/contrib/include/opencv2/contrib/retina.hpp

@@ -339,7 +339,7 @@ protected:
 	 * @param outputValarrayMatrix : the output valarray
 	 * @return the input image color mode (color=true, gray levels=false)
 	 */
-	const bool _convertCvMat2ValarrayBuffer(const cv::Mat inputMatToConvert, std::valarray<float> &outputValarrayMatrix);
+        bool _convertCvMat2ValarrayBuffer(const cv::Mat inputMatToConvert, std::valarray<float> &outputValarrayMatrix);
 
 	//! private method called by constructors, gathers their parameters and use them in a unified way
 	void _init(const Size inputSize, const bool colorMode, RETINA_COLORSAMPLINGMETHOD colorSamplingMethod=RETINA_COLOR_BAYER, const bool useRetinaLogSampling=false, const double reductionFactor=1.0, const double samplingStrenght=10.0);