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std::vector to cv::Mat

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0

what is the best way to convert a vector containing R,G and B color values in a cv::Vec3b vector to a cv::Mat? The position of the pixel does not matter, I just want to perform the cv::split operation and then put all three color levels to a histogramm.

I tried this, but it does not work as the split operation is returning a cv::Mat with only one plane of colors:

cv::Mat GetOnlyColoredPixel(cv::Mat& Gray, cv::Mat& Col) 
 std::vector<cv::Vec3b> ColorStack;
 cv::Vec3b vec;
 int nPixel = 0;

 for (int y = 0; y < Gray.rows; y++) 
 for (int x = 0; x < Gray.cols; x++) 
 if (Gray.at<unsigned char>(y, x) == 255) 
 ColorStack.push_back(Col.at<cv::Vec3b>(y, x));
 nPixel++;
 
 
 

 return cv::Mat(1, nPixel, CV_8UC3, &ColorStack[0]);

The strange thing is, that I really should have only yellow pixel but when printing the MAT object, I get all possible colors. The Col.at<cv::Vec3b>(y, x) returns the correct color but in RGB order - I thought, OpenCV is using BGR.

Thank you,
Jan

opencv vector colors mat

share|improve this question

edited Mar 27 at 15:49

Jan021981

asked Mar 27 at 15:12

Jan021981Jan021981

1281212 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  if that vector isn't changed anymore and doesn't go out of scope while you use the mat (before splitting), you can use the memory directly: cv::Mat testMat = cv:Mat(height, width, CV_8UC3, ColorStack.data()); then you can either split testMat or .clone it or whatever you like. Might be one copying of the data less than your approach, but will fail if the vector goes out of scope until you have done everything with testMat.
  
  – Micka
  Mar 27 at 16:07
  
  

  
  
  
  

add a comment | 

0

what is the best way to convert a vector containing R,G and B color values in a cv::Vec3b vector to a cv::Mat? The position of the pixel does not matter, I just want to perform the cv::split operation and then put all three color levels to a histogramm.

I tried this, but it does not work as the split operation is returning a cv::Mat with only one plane of colors:

cv::Mat GetOnlyColoredPixel(cv::Mat& Gray, cv::Mat& Col) 
 std::vector<cv::Vec3b> ColorStack;
 cv::Vec3b vec;
 int nPixel = 0;

 for (int y = 0; y < Gray.rows; y++) 
 for (int x = 0; x < Gray.cols; x++) 
 if (Gray.at<unsigned char>(y, x) == 255) 
 ColorStack.push_back(Col.at<cv::Vec3b>(y, x));
 nPixel++;
 
 
 

 return cv::Mat(1, nPixel, CV_8UC3, &ColorStack[0]);

The strange thing is, that I really should have only yellow pixel but when printing the MAT object, I get all possible colors. The Col.at<cv::Vec3b>(y, x) returns the correct color but in RGB order - I thought, OpenCV is using BGR.

Thank you,
Jan

opencv vector colors mat

share|improve this question

edited Mar 27 at 15:49

Jan021981

asked Mar 27 at 15:12

Jan021981Jan021981

1281212 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  if that vector isn't changed anymore and doesn't go out of scope while you use the mat (before splitting), you can use the memory directly: cv::Mat testMat = cv:Mat(height, width, CV_8UC3, ColorStack.data()); then you can either split testMat or .clone it or whatever you like. Might be one copying of the data less than your approach, but will fail if the vector goes out of scope until you have done everything with testMat.
  
  – Micka
  Mar 27 at 16:07
  
  

  
  
  
  

add a comment | 

what is the best way to convert a vector containing R,G and B color values in a cv::Vec3b vector to a cv::Mat? The position of the pixel does not matter, I just want to perform the cv::split operation and then put all three color levels to a histogramm.

I tried this, but it does not work as the split operation is returning a cv::Mat with only one plane of colors:

cv::Mat GetOnlyColoredPixel(cv::Mat& Gray, cv::Mat& Col) 
 std::vector<cv::Vec3b> ColorStack;
 cv::Vec3b vec;
 int nPixel = 0;

 for (int y = 0; y < Gray.rows; y++) 
 for (int x = 0; x < Gray.cols; x++) 
 if (Gray.at<unsigned char>(y, x) == 255) 
 ColorStack.push_back(Col.at<cv::Vec3b>(y, x));
 nPixel++;
 
 
 

 return cv::Mat(1, nPixel, CV_8UC3, &ColorStack[0]);

The strange thing is, that I really should have only yellow pixel but when printing the MAT object, I get all possible colors. The Col.at<cv::Vec3b>(y, x) returns the correct color but in RGB order - I thought, OpenCV is using BGR.

Thank you,
Jan

opencv vector colors mat

share|improve this question

edited Mar 27 at 15:49

Jan021981

asked Mar 27 at 15:12

Jan021981Jan021981

1281212 bronze badges

cv::Mat GetOnlyColoredPixel(cv::Mat& Gray, cv::Mat& Col) 
 std::vector<cv::Vec3b> ColorStack;
 cv::Vec3b vec;
 int nPixel = 0;

 for (int y = 0; y < Gray.rows; y++) 
 for (int x = 0; x < Gray.cols; x++) 
 if (Gray.at<unsigned char>(y, x) == 255) 
 ColorStack.push_back(Col.at<cv::Vec3b>(y, x));
 nPixel++;
 
 
 

 return cv::Mat(1, nPixel, CV_8UC3, &ColorStack[0]);

share|improve this question

edited Mar 27 at 15:49

Jan021981

asked Mar 27 at 15:12

Jan021981Jan021981

1281212 bronze badges

share|improve this question

edited Mar 27 at 15:49

Jan021981

asked Mar 27 at 15:12

Jan021981Jan021981

1281212 bronze badges

asked Mar 27 at 15:12

Jan021981Jan021981

1281212 bronze badges

asked Mar 27 at 15:12

Jan021981Jan021981

1281212 bronze badges

1 Answer
1

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oldest

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0

Ok, the returning is wrong. This code works fine:

cv::Mat GetOnlyColoredPixel(cv::Mat& Gray, cv::Mat& Col) 
std::vector<cv::Vec3b> ColorStack;
cv::Vec3b vec, vec2;

cv::imwrite("C:\HomeC\Test.bmp", Col);

for (int y = 0; y < Gray.rows; y++) 
 for (int x = 0; x < Gray.cols; x++) 
 if (Gray.at<unsigned char>(y, x) == 255) 
 //ColorStack.push_back(Col.at<cv::Vec3b>(y, x));
 vec = Col.at<cv::Vec3b>(y, x);
 ColorStack.push_back(vec);
 
 


cv::Mat RetVal = cv::Mat(1, ColorStack.size(), CV_8UC3);
memcpy(RetVal.data, ColorStack.data(), ColorStack.size() * sizeof(cv::Vec3b));
return RetVal;

share|improve this answer

answered Mar 27 at 16:03

Jan021981Jan021981

1281212 bronze badges

add a comment | 

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0

Ok, the returning is wrong. This code works fine:

cv::Mat GetOnlyColoredPixel(cv::Mat& Gray, cv::Mat& Col) 
std::vector<cv::Vec3b> ColorStack;
cv::Vec3b vec, vec2;

cv::imwrite("C:\HomeC\Test.bmp", Col);

for (int y = 0; y < Gray.rows; y++) 
 for (int x = 0; x < Gray.cols; x++) 
 if (Gray.at<unsigned char>(y, x) == 255) 
 //ColorStack.push_back(Col.at<cv::Vec3b>(y, x));
 vec = Col.at<cv::Vec3b>(y, x);
 ColorStack.push_back(vec);
 
 


cv::Mat RetVal = cv::Mat(1, ColorStack.size(), CV_8UC3);
memcpy(RetVal.data, ColorStack.data(), ColorStack.size() * sizeof(cv::Vec3b));
return RetVal;

share|improve this answer

answered Mar 27 at 16:03

Jan021981Jan021981

1281212 bronze badges

add a comment | 

0

Ok, the returning is wrong. This code works fine:

cv::Mat GetOnlyColoredPixel(cv::Mat& Gray, cv::Mat& Col) 
std::vector<cv::Vec3b> ColorStack;
cv::Vec3b vec, vec2;

cv::imwrite("C:\HomeC\Test.bmp", Col);

for (int y = 0; y < Gray.rows; y++) 
 for (int x = 0; x < Gray.cols; x++) 
 if (Gray.at<unsigned char>(y, x) == 255) 
 //ColorStack.push_back(Col.at<cv::Vec3b>(y, x));
 vec = Col.at<cv::Vec3b>(y, x);
 ColorStack.push_back(vec);
 
 


cv::Mat RetVal = cv::Mat(1, ColorStack.size(), CV_8UC3);
memcpy(RetVal.data, ColorStack.data(), ColorStack.size() * sizeof(cv::Vec3b));
return RetVal;

share|improve this answer

answered Mar 27 at 16:03

Jan021981Jan021981

1281212 bronze badges

add a comment | 

Ok, the returning is wrong. This code works fine:

cv::Mat GetOnlyColoredPixel(cv::Mat& Gray, cv::Mat& Col) 
std::vector<cv::Vec3b> ColorStack;
cv::Vec3b vec, vec2;

cv::imwrite("C:\HomeC\Test.bmp", Col);

for (int y = 0; y < Gray.rows; y++) 
 for (int x = 0; x < Gray.cols; x++) 
 if (Gray.at<unsigned char>(y, x) == 255) 
 //ColorStack.push_back(Col.at<cv::Vec3b>(y, x));
 vec = Col.at<cv::Vec3b>(y, x);
 ColorStack.push_back(vec);
 
 


cv::Mat RetVal = cv::Mat(1, ColorStack.size(), CV_8UC3);
memcpy(RetVal.data, ColorStack.data(), ColorStack.size() * sizeof(cv::Vec3b));
return RetVal;

share|improve this answer

answered Mar 27 at 16:03

Jan021981Jan021981

1281212 bronze badges

cv::Mat GetOnlyColoredPixel(cv::Mat& Gray, cv::Mat& Col) 
std::vector<cv::Vec3b> ColorStack;
cv::Vec3b vec, vec2;

cv::imwrite("C:\HomeC\Test.bmp", Col);

for (int y = 0; y < Gray.rows; y++) 
 for (int x = 0; x < Gray.cols; x++) 
 if (Gray.at<unsigned char>(y, x) == 255) 
 //ColorStack.push_back(Col.at<cv::Vec3b>(y, x));
 vec = Col.at<cv::Vec3b>(y, x);
 ColorStack.push_back(vec);
 
 


cv::Mat RetVal = cv::Mat(1, ColorStack.size(), CV_8UC3);
memcpy(RetVal.data, ColorStack.data(), ColorStack.size() * sizeof(cv::Vec3b));
return RetVal;

share|improve this answer

answered Mar 27 at 16:03

Jan021981Jan021981

1281212 bronze badges

answered Mar 27 at 16:03

Jan021981Jan021981

1281212 bronze badges

answered Mar 27 at 16:03

Jan021981Jan021981

1281212 bronze badges