OpenCv assertion failed about rect ROI

Question

I am trying writing image rotation,but I have some problem right now. This is my code:

Mat rotateMagnify (Mat& img, int degree){
double angle = degree  * CV_PI / 180.;
double a = sin(angle), b = cos(angle);

int width = img.cols, height = img.rows;

int width_rotate = int(height * fabs(b) - width * fabs(a) + width);
int height_rotate = int(width * fabs(a) + height * fabs(b) + height);

Mat img_rotate;
img_rotate.create((width_rotate, height_rotate), img.depth(), img.channels());


int tempLength = sqrt((double)width * width + (double)height *height) + 10;
int tempX = (tempLength + 1) / 2 - width / 2;
int tempY = (tempLength + 1) / 2 - height / 2;


Mat temp;
temp.create((tempLength, tempLength), img.depth(), img.channels());
//cvZero(&img_rotate);

Mat roiImage = temp(Rect(Point(tempX, tempY), Point(width, height)));

//roiImage.ResetImageROI(roiImage);

img.copyTo(roiImage);

float m[6];
int w = roiImage.cols;
int h = roiImage.rows;
m[0] = b;
m[1] = a;
m[3] = -m[1];
m[4] = m[0];

m[2] = w * 0.5f;
m[5] = h * 0.5f;
CvMat M = cvMat(2, 3, CV_32F, m);

cvGetQuadrangleSubPix(&roiImage, &img_rotate, &M);
roiImage.release();

return img_rotate;}

Unfortunately this code does not work. I get error like this:

OpenCV Error: Assertion failed (0 <= roi.x && 0 <= roi.width && roi.x + 
roi.width <= m.cols && 0 <= roi.y && 0 <= roi.height && roi.y + roi.height 
<= m.rows) in cv::Mat::Mat, file C:\builds\master_PackSlave-win32-vc12-
shared\opencv\modules\core\src\matrix.cpp, line 495

How can I fix this error. Thank You all for help!

Try interchanging the `width` and `height` parameters.... and then give it a try — Jeru Luke, Apr 25 '17 at 16:53
print out the dimensions at run time and you should figure out why it is happening — chris, Apr 26 '17 at 10:53

score 2 · Answer 1 · answered Apr 26 '17 at 10:47

This error is usually thrown when you try to copy(crop) a part of an image but x,y value you are specifying is either -ve or its more than the size of the actual image. Add breakpoint and check values of int tempX = (tempLength + 1) / 2 - width / 2; int tempY = (tempLength + 1) / 2 - height / 2; try to handle above mentioned condition before you try

Mat roiImage = temp(Rect(Point(tempX, tempY), Point(width, height)));

//roiImage.ResetImageROI(roiImage);

img.copyTo(roiImage);

OpenCv assertion failed about rect ROI

1 Answers1