OpenCV c++ template recognition - c++

Question

I have a template and I want to know if the template is present in an image. Well I have googled a lot and came to the conclusion that I need to use cvMatchTemplate and cvMinMaxLoc.
Here is my code:
image = cvLoadImage("C:/images/flower.jpg",1);
templat = cvLoadImage("C:/images/flo.jpg",1);
image2=cvCreateImage( cvSize(image->width, image->height), IPL_DEPTH_8U, 1 );
result=cvCreateImage( cvSize(image->width, image->height), IPL_DEPTH_8U, 1 );
cvZero(result);
cvZero(image2);
cvCvtColor(image,image2,CV_BGR2GRAY);
cvMatchTemplate(image2, templat,result,CV_TM_CCORR_NORMED);
double min_val=0, max_val=0;
CvPoint min_loc, max_loc;
cvMinMaxLoc(result, &min_val, &max_val, &min_loc, &max_loc);
cvRectangle(image, max_loc, cvPoint(max_loc.x+templat->width,
max_loc.y+templat->height), cvScalar(0), 1);
cvShowImage( "src", image );
cvShowImage( "result image", result);
cvWaitKey(0);
My problem is when I run the above code,a message box is displayed saying:
Unhandled exception at 0x747d812f in matching.exe: Microsoft C++ exception: cv::Exception at memory location 0x001ff6ec..
and in the black screen there is a message:
OpenCV Error: Sizes of input arguments do not match <image and template should have the same type> in unknown function, file..\..\..\..\ocv\opencv\scr\cv\cvtempl.cpp, line 356.
Please note that flower.jpg is a coloured image and flo.jpg is the gray scale of that image.
Any ideas of what is happening?

Answer 1

You need to convert both flower.jpg and flo.jpg to single-channel image. Even if flo.jpg is grayscale, you're loading it as three-channel image. Also the result image should be IPL_DEPTH_32F instad of IPL_DEPTH_8U.
Here is the correct code (untested):
IplImage* image = cvLoadImage("C:/images/flower.jpg", 1);
IplImage* templat = cvLoadImage("C:/images/flo.jpg", 1);
IplImage* image2 = cvCreateImage(cvSize(image->width, image->height), IPL_DEPTH_8U, 1);
IplImage* templat2 = cvCreateImage(cvSize(templat->width, templat->height), IPL_DEPTH_8U, 1);
cvCvtColor(image, image2, CV_BGR2GRAY);
cvCvtColor(templat, templat2, CV_BGR2GRAY);
int w = image->width - templat->width + 1;
int h = image->height - templat->height + 1;
result = cvCreateImage(cvSize(w, h), IPL_DEPTH_32F, 1);
cvMatchTemplate(image2, templat, result, CV_TM_CCORR_NORMED);
double min_val, max_val;
CvPoint min_loc, max_loc;
cvMinMaxLoc(result, &min_val, &max_val, &min_loc, &max_loc);
cvRectangle(image, max_loc, cvPoint(max_loc.x+templat->width,
max_loc.y+templat->height), cvScalar(0), 1);
cvShowImage("src", image);
cvShowImage("result image", result);
cvWaitKey(0);

Answer 2

Template matching assumes that both image and template have identical number of channels and channel depth. The simplest way to do is to load both of them in grayscale:
Mat I = imread("lena.png", 0);
Mat T = imread("template.png", 0);
Notes: I would command to use OpenCV2.0 C++ interface. So instead of cvLoadImage use imread. The old interface is no longer developed.