I want to limit a SurfFeatureDetector to a set of regions (mask). For a test I define only a single mask:
Mat srcImage; //RGB source image
Mat mask = Mat::zeros(srcImage.size(), srcImage.type());
Mat roi(mask, cv::Rect(10,10,100,100));
roi = Scalar(255, 255, 255);
SurfFeatureDetector detector();
std::vector<KeyPoint> keypoints;
detector.detect(srcImage, keypoints, roi); // crash
//detector.detect(srcImage, keypoints); // does not crash
When I pass the "roi" as the mask I get this error:
OpenCV Error: Assertion failed (mask.empty() || (mask.type() == CV_8UC1 && mask.size() == image.size())) in detect, file /Users/ux/Downloads/OpenCV-iOS/OpenCV-iOS/../opencv-svn/modules/features2d/src/detectors.cpp, line 63
What is wrong with this? How can I correctly pass a mask to the SurfFeatureDetector's "detect" method?
Regards,
Two things about the mask.
CV_8U
. In your case the mask is of type srcImage.type(), which is a 3-channel matrixroi
to the detector but you should be passing mask
. When you are making changes to roi
, you are also changing mask
.the following should work
Mat srcImage; //RGB source image
Mat mask = Mat::zeros(srcImage.size(), CV_8U); // type of mask is CV_8U
// roi is a sub-image of mask specified by cv::Rect object
Mat roi(mask, cv::Rect(10,10,100,100));
// we set elements in roi region of the mask to 255
roi = Scalar(255);
SurfFeatureDetector detector();
std::vector<KeyPoint> keypoints;
detector.detect(srcImage, keypoints, mask); // passing `mask` as a parameter