Accessing certain pixel RGB value in openCV

Question

I have searched internet and stackoverflow thoroughly  but I haven t found answer to my question   How can I get set  both  RGB value of certain  given by x y coordinates  pixel in OpenCV  What s important-I m writing in C    the image is stored in cv  Mat variable  I know there is an IplImage   operator  but IplImage is not very comfortable in use-as far as I know it comes from C API   Yes  I m aware that there was already this Pixel access in OpenCV 2 2 thread  but it was only about black and white bitmaps   EDIT   Thank you very much for all your answers  I see there are many ways to get set RGB value of pixel  I got one more idea from my close friend-thanks Benny  It s very simple and effective  I think it s a matter of taste which one you choose   Mat image           Point3  lt uchar gt   p   image ptr lt Point3  lt uchar gt   gt  y x     And then you can read write RGB values with   p- gt x   B p- gt y   G p- gt z   R

User · Answer

The low-level way would be to access the matrix data directly. In an RGB image (which I believe OpenCV typically stores as BGR), and assuming your cv::Mat variable is called frame, you could get the blue value at location (x, y) (from the top left) this way:

frame.data[frame.channels()*(frame.cols*y + x)];

Likewise, to get B, G, and R:

uchar b = frame.data[frame.channels()*(frame.cols*y + x) + 0];    
uchar g = frame.data[frame.channels()*(frame.cols*y + x) + 1];
uchar r = frame.data[frame.channels()*(frame.cols*y + x) + 2];

Note that this code assumes the stride is equal to the width of the image.

User · Answer

const double pi   boost  math  constants  pi lt double gt      cv  Mat distance2ellipse cv  Mat image  cv  RotatedRect ellipse       float distance   2 0f      float angle   ellipse angle      cv  Point ellipse center   ellipse center      float major axis   ellipse size width 2      float minor axis   ellipse size height 2      cv  Point pixel      float a b c d       for int x   0  x  lt  image cols  x                  for int y   0  y  lt  image rows  y                       auto u    cos angle pi 180   x-ellipse center x    sin angle pi 180   y-ellipse center y           auto v   -sin angle pi 180   x-ellipse center x    cos angle pi 180   y-ellipse center y            distance    u major axis   u major axis     v minor axis   v minor axis              if distance lt  1                        image at lt cv  Vec3b gt  y x  1    255                          return image

User · Answer

A piece of code is easier for people who have such problem  I share my code and you can use it directly  Please note that OpenCV store pixels as BGR   cv  Mat vImage     if src         cv  Vec3f vec        for int i   0  i  lt  vHeight   i            for int j   0  j  lt  vWidth   j                          vec    cv  Vec3f   src   0  255 0    src   1  255 0    src   2  255 0    Please note that OpenCV store pixels as BGR               vImage  at lt cv  Vec3f gt  vHeight -1-i  j    vec                  src                if   vImage  data      Check for invalid input     printf  failed to read image by OpenCV     else       cv  namedWindow  windowName   CV WINDOW AUTOSIZE       cv  imshow  windowName   vImage       Show the image

User · Answer

Try the following   cv  Mat image      do some stuff       image at lt cv  Vec3b gt  y x   gives you the RGB  it might be ordered as BGR  vector of type cv  Vec3b  image at lt cv  Vec3b gt  y x  0    newval 0   image at lt cv  Vec3b gt  y x  1    newval 1   image at lt cv  Vec3b gt  y x  2    newval 2

User · Answer

The current version allows the cv  Mat  at function to handle 3 dimensions  So for a Mat object m  m at lt uchar gt  0 0 0  should work

User · Answer

uchar   value   img2 data    Pointer to the first pixel data  it s return array in all values  int r   2  for  size t i   0  i  lt  img2 cols   img2 rows   img2 channels     i               if  r  gt  2  r   0           if  r    0  value i    0          if  r    1 value i     0          if  r    2 value i    255           r

[c++] Accessing certain pixel RGB value in openCV

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