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

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

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

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

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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

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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

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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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