I am using Raspberry Pi 2 model B with Rasbian OS.
I am first finding the largest contour from the image, then I am extracting the contour alone using a bounding rectangle (cropping). Then in this cropped image I want to pad zeroes over all the four edges.
Main Objective: is to pad zeroes in all the four sides of the cropped image.
It is working perfectly fine till the cropping part. But after padding the image is changed in a funny way.
This is the source image:
From this I have cropped our ROI and saved it in a different matrix:
The following is the code I am using for finding largest contour and cropping:
Mat find_screen_contour( Mat src )
{
double largest_area=0;
int largest_contour_index=0;
Rect bounding_rect;
vector< vector<Point> > contours; // Vector for storing contour
vector<Vec4i> hierarchy;
findContours( src, contours, hierarchy,CV_RETR_CCOMP, CV_CHAIN_APPROX_SIMPLE );
// iterate through each contour.
for( int i = 0; i< contours.size(); i++ )
{
// Find the area of contour
double a=contourArea( contours[i],false);
if(a>largest_area){
largest_area=a;
cout<<i<<" area "<<a<<endl;
// Store the index of largest contour
largest_contour_index=i;
// Find the bounding rectangle for biggest contour
bounding_rect = boundingRect(contours[i]);
}
}
cout << "largest contour index: " << largest_contour_index << endl;
Scalar color( 255,255,255); // color of the contour in the
//Draw the contour and rectangle
drawContours( src, contours,largest_contour_index, color, -1,8,hierarchy); //-1 for filling the contour
/*cropping*/
Mat cropped_img;
src( bounding_rect ).copyTo( cropped_img );
return cropped_img;
}
The returned cropped_img will be the cropped image I attached above.
Next is the padding part:
Mat pad_zero(Mat src, int pad_thick = 20)
{
//dst: create a new Mat with larger size than source image and
//fill with 0s
Mat dst = Mat(src.size()+ Size(pad_thick*2, pad_thick*2), src.type() ,0.0);
//traverse through each pixel and set the value to the new Matrix
for(int x=0 ; x<src.rows ; x++)
{
for(int y=0 ; y<src.cols ; y++)
{
const Vec3b &px = src.at<Vec3b>(x,y);
dst.at<Vec3b>(x+pad_thick, y+pad_thick)[0] = px[0];
dst.at<Vec3b>(x+pad_thick, y+pad_thick)[1] = px[1];
dst.at<Vec3b>(x+pad_thick, y+pad_thick)[2] = px[2];
//dst.at<Vec3b>(x+pad_thick, y+pad_thick) = px;
}
}
return dst;
}
The returned image dst is:
But if the same code (ie, absolutely without any change!!) is run in Visual Studio in Windows 8.1, we get the desired image, which is:
The image seems to have stretched somewhat and broken in the right. What could be the problem?
I tried changing the copying pixel values part since we are working on Grayscale (single channel).
From:
dst.at<Vec3b>(x+pad_thick, y+pad_thick)[0] = px[0];
dst.at<Vec3b>(x+pad_thick, y+pad_thick)[1] = px[1];
dst.at<Vec3b>(x+pad_thick, y+pad_thick)[2] = px[2];
To:
dst.at<Vec3b>(x+pad_thick, y+pad_thick)[0] = px[0]; //or [1] or [2]
And to:
dst.at<Vec3b>(x+pad_thick, y+pad_thick) = px; //without specifying channel
The former yielded a different image but that also was a wrong image. The latter gave the same output as the original code with three channels. I would be really glad if I get help. Thanks in advance.
