c and opencv get and set pixel color to Mat

Question

I m trying to set a new color value to some pixel into a cv  Mat image my code is below       Mat image   img      for int y 0 y lt img rows y                  for int x 0 x lt img cols x                      Vec3b color   image at lt Vec3b gt  Point x y            if color 0   gt  150  amp  amp  color 1   gt  150  amp  amp  color 2   gt  150                        color 0    0              color 1    0              color 2    0              cout  lt  lt   Pixel  gt 200     lt  lt  x  lt  lt       lt  lt  y  lt  lt  endl                    else                       color val 0    255              color val 1    255              color val 2    255                      imwrite     images imgopti  to string i    tiff  image     It seems to get the good pixel in output  with cout  however in the output image  with imwrite  the pixel concerned aren t modified  I have already tried using color val 0    I still can t figure out why the pixel colors in the output image dont change  thanks

User · Answer

just use a reference   Vec3b  amp  color   image at lt Vec3b gt  y x   color 2    13

User · Answer

You did everything except copying the new pixel value back to the image   This line takes a copy of the pixel into a local variable   Vec3b color   image at lt Vec3b gt  Point x y      So  after changing color as you require  just set it back like this   image at lt Vec3b gt  Point x y     color    So  in full  something like this   Mat image   img  for int y 0 y lt img rows y          for int x 0 x lt img cols x                     get pixel         Vec3b  amp  color   image at lt Vec3b gt  y x                   do something to the color              color 0    13          color 1    13          color 2    13              set pixel           image at lt Vec3b gt  Point x y     color            if you copy value

User · Answer

I would not use  at for performance reasons   Define a struct      pragma pack push  2    not useful  see comments below  struct RGB       uchar blue      uchar green      uchar red        And then use it like this on your cv  Mat image   RGB amp  rgb   image ptr lt RGB gt  y  x     image ptr y  gives you a pointer to the scanline y  And iterate through the pixels with loops of x and y

[c++] c++ and opencv get and set pixel color to Mat

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