OpenCV image conversion from RGB to Grayscale exception -

i'm getting strange exception (exception: cv::exception @ memory location 0x002eb6cc) when try convert rgb image grayscale. can me?

  const cv::mat img1 = cv::imread(filename, 0)   cv::mat gs_rgb(img1.size(), cv_8uc1);   cv::cvtcolor(img1, gs_rgb, cv_rgb2gray); 

you loading image gray scale , trying convert gray scale gray scale again.

the line

  const cv::mat img1 = cv::imread(filename, 0) 

will load image

where second argument

=0->cv_load_image_grayscale->load gray scale =1->cv_load_image_color->load color <0->cv_load_image_anydepth->return loaded image (with alpha channel). 

so either load image gray scale , use like,

  const cv::mat img1 = cv::imread(filename, 0)//load gray 

or load color , convert gray scale like,

  const cv::mat img1 = cv::imread(filename, 1);//load color   mat gray;//no need of allocation, allocate automatically.   cv::cvtcolor(img1,gray, cv_bgr2gray);//opencv default color order bgr 

see more info here in imread documentation.