OpenCV: How to iterate each pixel in a specific area of an image

问题

I have an Image(see below) that is marked by two parallel green lines. This image is read in a OpenCV Mat in C++, the slope of green lines and their distances to the image center are already known.

Now I want to iterate all the pixels in the area between these two green lines. How can i solve this problem? It will be very helpful, if somebody can give me a code example.

Many thanks.

回答1:

The formula for a slope is the following:

y = mx + b

Since you have two of them you should have two slope formulas:

y1 = m1x1 + b1
y2 = m2x2 + b2

m1, m2, b1, b2 should be known.

All you have to do is start at y1 = 0 and y2 = 0, and iterate between x1 to x2 for each y1 = y2 from top to bottom.

Example code:

for (int y = 0; y < imageHeight; ++y)
{
    int x1 = (y - b1) / m1;
    int x2 = (y - b2) / m2;

    for (int x = x1; x < x2; ++x)
    {
        // Do something.
    }
}

回答2:

you could use LineIterator

take a look at the sample code below

#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>

using namespace std;
using namespace cv;

int main( int, char** argv )
{
    Mat src;
    src = imread( argv[1] );

    if( src.empty() )
    {
        return -1;
    }

    Point pt1 = Point( (src.cols / 5) + (src.cols / 8), src.rows);
    Point pt2 = Point( (src.cols ) - (src.cols / 8), 0);

    LineIterator it(src, pt1, pt2, 8);

    for(int y = 0; y < it.count; y++, ++it)
    {
        Point it_pos = it.pos();
        for(int x = it_pos.x; x < it_pos.x+(src.cols / 5) & x < src.cols; x++)
        {
            Vec3b & pixel = src.at<Vec3b>(it_pos.y,x);
            pixel = pixel * 1.3;
            pixel[0] = 0;
        }

    }

    imshow("result", src );
    waitKey(0);

    return 0;

}

result images (look edit history to understand changes well):

来源：https://stackoverflow.com/questions/36970099/opencv-how-to-iterate-each-pixel-in-a-specific-area-of-an-image

标签

c++

OpenCV

pixel