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POSegmentation Fault (core dumped) in pixel manipulation
 

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  1. POSegmentation Fault (core dumped) in pixel manipulation
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    <p>I am trying to get the bird's eye view of an image. I am altering the pixel intensity in two <em>for-loops</em> going over row and column respectively. </p> <pre><code>birdeyeview_img.at&lt;uchar&gt;(p,q)=(int)undistor_img.at&lt;uchar&gt;(round(corr_x),round(corr_y); </code></pre> <p>I am getting: <code>Segmentation Fault (Core Dumped)</code>. How do I alter the pixel intensity, without getting nay such error? My undistorted image is a grayscale image. Now I made few changes, it runs but doesn't give proper result, only a part of the code shows pixel manipulations : // </p> <pre><code>This code will take undistorted images as input and give the bird's eye view using them // First we need to calculate the homography matrix #include "opencv2/highgui/highgui.hpp" #include "opencv2/core/core.hpp" #include "opencv2/imgproc/imgproc_c.h" #include &lt;iostream&gt; #include &lt;stdio.h&gt; #include &lt;stdlib.h&gt; #include &lt;math.h&gt; using namespace cv; using namespace std; int main() { //loading the undistorted image Mat undistor_img=imread("undistorted images/img_u1.jpg", CV_WINDOW_AUTOSIZE); namedWindow("undistorted image"); imshow("undistorted image",undistor_img); // storing the resolution values float resolution_x=50, resolution_y=50; // height and width for bird's eye view float heightBirdEyeView=500; float widthBirdEyeView=700; //camera height and tilt float height_camera = 125; float tilt_camera=12; float halfAngle=180; float pi=3.14159; float alpha = tilt_camera/halfAngle*pi; //focal length in x and y float focal_length_x = 354.05700; float focal_length_y = 353.65297; //generate transformation matrix float H1[3][3]={resolution_x,0,widthBirdEyeView/2+1, 0,-1*resolution_y,heightBirdEyeView, 0,0,1}; Mat transformation_matrix(3,3,CV_32FC1,H1); cout&lt;&lt;"transformation matrix="&lt;&lt;endl&lt;&lt;transformation_matrix&lt;&lt;endl&lt;&lt;endl; //generate top view matrix float H2[3][3]={height_camera/focal_length_x,0,0, 0,0,height_camera, 0,cos(alpha)/focal_length_y,sin(alpha)}; Mat topview_matrix(3,3,CV_32FC1,H2); cout&lt;&lt;"topview matrix="&lt;&lt;endl&lt;&lt;topview_matrix&lt;&lt;endl&lt;&lt;endl; //generate scale matrix float H3[3][3]={1,0,undistor_img.rows, 0,1,undistor_img.rows, 0,0,1}; Mat scale_matrix(3,3,CV_32FC1,H3); cout&lt;&lt;"scale matrix="&lt;&lt;endl&lt;&lt;scale_matrix&lt;&lt;endl&lt;&lt;endl; //generate the homography matrix from these matrices Mat homography_matrix=transformation_matrix*topview_matrix/scale_matrix; cout&lt;&lt;"homography matrix"&lt;&lt;endl&lt;&lt;homography_matrix&lt;&lt;endl&lt;&lt;endl; cout&lt;&lt;homography_matrix.at&lt;float&gt;(0,0)&lt;&lt;endl; //now we need transpose of homography matrix Mat transpose_homography_matrix(3,3,CV_32FC1); for(int i=0;i&lt;3;i++) { for(int j=0;j&lt;3;j++) transpose_homography_matrix.at&lt;float&gt;(i,j)=homography_matrix.at&lt;float&gt;(j,i); } cout&lt;&lt;"transpose of homography matrix"&lt;&lt;endl&lt;&lt;transpose_homography_matrix&lt;&lt;endl&lt;&lt;endl; Mat birdeyeview_img(heightBirdEyeView, widthBirdEyeView,CV_32FC3); namedWindow("bird's eye view image"); Mat p_new(3,1,CV_32FC1); // this will give the coordinates in the bird's eye view float corrected_x,corrected_y; int a=0,b=0; // counters for if and else blocks //now we need matrix with coordinates of the image plane, to be projected for(int p=0; p&lt;heightBirdEyeView;p++) { uchar* data= undistor_img.ptr&lt;uchar&gt;(p); uchar* hdata= birdeyeview_img.ptr&lt;uchar&gt;(p); for(int q=0;q&lt;widthBirdEyeView;q++) { int M[]={q,p,1}; Mat p_old(3,1,CV_32FC1,M); //holding the positions in undistorted image //cout&lt;&lt;transpose_homography_matrix*p_old&lt;&lt;endl; p_new=transpose_homography_matrix*p_old; corrected_x=p_new.at&lt;float&gt;(0,0)/p_new.at&lt;float&gt;(2,0); corrected_y=p_new.at&lt;float&gt;(1,0)/p_new.at&lt;float&gt;(2,0); if (((abs(corrected_y)&gt;=1)&amp;&amp;(corrected_y&lt;=undistor_img.rows))&amp;&amp;((abs(corrected_x)&gt;=1)&amp;&amp;(corrected_x&lt;=undistor_img.cols))) { /*hdata[q]=(1- (corrected_y-floor(corrected_y)))*(1-(corrected_x-floor(corrected_x)))*data[q] +(1-( corrected_y-floor(corrected_y)))*(corrected_x-floor(corrected_x))*data[q] +( corrected_y-floor(corrected_y))*(1-(corrected_x-floor(corrected_x)))*data[q] +( corrected_y-floor(corrected_y))*(corrected_x-floor(corrected_x))*data[q];*/ hdata[q]=(1- (corrected_y-floor(corrected_y)))*(1-(corrected_x-floor(corrected_x)))*(undistor_img.at&lt;uchar&gt;(floor(corrected_y),floor(corrected_x)))+(1-( corrected_y-floor(corrected_y)))*(corrected_x-floor(corrected_x))*(undistor_img.at&lt;uchar&gt;(floor(corrected_y), ceil(corrected_x)))+(corrected_y-floor(corrected_y))*(1-(corrected_x-floor(corrected_x)))*(undistor_img.at&lt;uchar&gt;(ceil(corrected_y),floor(corrected_x)))+(corrected_y-floor(corrected_y))*(corrected_x-floor(corrected_x))*(undistor_img.at&lt;uchar&gt;(ceil(corrected_y), ceil(corrected_x))); a++;} else{ b++; hdata[q]= undistor_img.at&lt;uchar&gt;(p,q); } } } //cout&lt;&lt;"if was read"&lt;&lt;a &lt;&lt;"times"&lt;&lt;endl; //cout&lt;&lt;"else was read"&lt;&lt;b &lt;&lt;"times"&lt;&lt;endl; imshow("bird's eye view image",birdeyeview_img); //cout&lt;&lt;"input size="&lt;&lt;undistor_img.rows&lt;&lt;"X"&lt;&lt;undistor_img.cols&lt;&lt;endl; //cout&lt;&lt;"result size="&lt;&lt;birdeyeview_img.rows&lt;&lt;"X"&lt;&lt;birdeyeview_img.cols&lt;&lt;endl; cvWaitKey(); } </code></pre> <p>In what other ways can I change pixel values(in birdeyeview_img) , using the pixel values from another image (undistor_img) ?</p>
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    1. USMojo Jojo
    1. USMojo Jojo
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      1. POSegmentation Fault (core dumped) in pixel manipulation
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      1. VTApproveEditSuggestion
    1. CODifficult to comment unless you post a bit more code, such as the lines where you allocate birdeyeview_img, undistor_img, etc.
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      1. POSegmentation Fault (core dumped) in pixel manipulation
      1. USTotoro
    2. COPlease provide at least the image size, depth, and `p`,`q`,`corr_x`,`corr_y`
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      1. POSegmentation Fault (core dumped) in pixel manipulation
      1. USAlex
    3. COIf You are using linux, then You can use `ulimit -c unlimited` to get the core dump file when You encounter segfault, and then use gdb to check precisely where it crashed: `gdb my_awsome_app core`. You will need tocompile with -g option to place debuugsymbols in your application. When You started `gdb` use `bt` to get backtrace of functions that were called until the crash.
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      1. POSegmentation Fault (core dumped) in pixel manipulation
      1. USmorynicz
 

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