Pixel access in OpenCV 2.2

问题

Hi I want to use opencv to tell me the pixel values of a blank and white image so the output would look like this

Here is my current code but I\'m not sure how to access the results of the CV_GET_CURRENT call.. any help ?

IplImage readpix(IplImage*  m_image) {


  cout << \"Image width  : \" << m_image->width << \"\\n\"; 
  cout << \"Image height : \" << m_image->height << \"\\n\"; 
  cout << \"-----------------------------------------\\n\"; 


  CvPixelPosition8u position;

  CV_INIT_PIXEL_POS(position, (unsigned char*)(m_image->imageData), m_image->widthStep, cvSize(m_image->width, m_image->height), 0, 0, m_image->origin);

  for(int y = 0; y < m_image->height; ++y) // FOR EACH ROW
  {
    for(int x = 0; x < m_image->width; ++x) // FOR EACH COL 
      {
        CV_MOVE_TO(position, x, y, 1);
        unsigned char colour = *CV_GET_CURRENT(position, 1);

// I want print 1 for a black pixel or 0 for a white pixel 
// so i want goes here


      }

  cout << \" \\n\"; //END OF ROW

  }
}

回答1:

In opencv 2.2, I'd use the C++ interface.

cv::Mat in = /* your image goes here, 
                assuming single-channel image with 8bits per pixel */
for(int row = 0; row < in.rows; ++row) {
    unsigned char* inp  = in.ptr<unsigned char>(row);
    for (int col = 0; col < in.cols; ++col) {
        if (*inp++ == 0) {
            std::cout << '1';
        } else {
            std::cout << '0';
        }
        std::cout << std::endl;
    }
}

回答2:

IplImage struct have a variable char* imageData - it's just a buffer of all pixels. To read it properly you have to know your image format. For example for RGB888 image 3 first chars in imageData array will represent the r,g,b values of the first pixel at the first row. If you know the image format - you can read the data properly. Image format can be restored reading another values of IplImage structure:

http://opencv.willowgarage.com/documentation/basic_structures.html

Also i think it's more efficient to write the loop like this:

uchar r,g,b;

for (int y = 0; y < cvFrame->height; y++)
{
    uchar *ptr = (uchar*) (cvFrame_->imageData + y*cvFrame_->widthStep);
    for (int x = 0; x < cvFrame_->width; x++)
    {       
        r = ptr[3*x];
        g = ptr[3*x + 1];
        b = ptr[3*x + 2];
    }
}

This code is for RGB888 image

回答3:

IplImage is the old format for images. You should use the new format, CvMat, which can store arbitrary matrices. An image is just a matrix, after all.

You can then access the pixels using the function cvGet2D, which returns a CvScalar.

来源：https://stackoverflow.com/questions/4742251/pixel-access-in-opencv-2-2

标签

image-processing

OpenCV

computer-vision

pixel