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Hi,

I'm currently working on replicating the Canny edge detector in OpenCV. I've managed to replicate the built-in Sobel operator using a 3x3 Gaussian filter and by calculating the magnitude as a weighted sum of absolute values of Gx and Gy (L2gradient is set to FALSE when calling Canny).

Sample outputs below:

original image

OpenCV Sobel

My Sobel operator

My Sobel operator after non-max

OpenCV Canny (L2gradient = FALSE)

My Canny ED

I assume the problem is in thresholding. This is how I imagined doing it:

for (int rows = 1; rows < height-1; rows++)
{
    for (int cols = 1; cols < width-1; cols++)
    {
        temp = custom_canny.at<uint8_t>(rows, cols);

        //thresholding
        if (temp >= THRESHOLD_HIGH) temp = 255;
        else if (temp < THRESHOLD_LOW) temp = 0;

        else
        {
            if (cannypixels[rows * width + cols - 1] >= THRESHOLD_HIGH || cannypixels[rows * width + cols + 1] >= THRESHOLD_HIGH || cannypixels[(rows - 1) * width + cols] >= THRESHOLD_HIGH || cannypixels[(rows + 1) * width + cols] >= THRESHOLD_HIGH || cannypixels[(rows + 1) * width + cols - 1] >= THRESHOLD_HIGH || cannypixels[(rows - 1) * width + cols - 1] >= THRESHOLD_HIGH || cannypixels[(rows - 1) * width + cols + 1] >= THRESHOLD_HIGH || cannypixels[(rows + 1) * width + cols + 1] >= THRESHOLD_HIGH) temp = 255;
            else temp = 0;
            //temp = custom_canny.at<uint8_t>(rows, cols); //255;
        }

        temp_canny.at<uint8_t>(rows, cols) = temp;
        //printf("%d\t", ocv_canny_false.at<uint8_t>(rows, cols));
    }
    //printf("\n");
}

I'd be grateful for any ideas on what the problem might be.

Hi,

I'm currently working on replicating the Canny edge detector in OpenCV. I've managed to replicate the built-in Sobel operator using a 3x3 Gaussian filter and by calculating the magnitude as a weighted sum of absolute values of Gx and Gy (L2gradient is set to FALSE when calling Canny).

Sample outputs below:

original image

OpenCV Sobel

My Sobel operator

My Sobel operator after non-max

OpenCV Canny (L2gradient = FALSE)

My Canny ED

I assume the problem is in thresholding. This is how I imagined doing it:

for (int rows = 1; rows < height-1; rows++)
{
    for (int cols = 1; cols < width-1; cols++)
    {
        temp = custom_canny.at<uint8_t>(rows, cols);

        //thresholding
        if (temp >= THRESHOLD_HIGH) temp = 255;
        else if (temp < THRESHOLD_LOW) temp = 0;

        else
        {
            if (cannypixels[rows * width + cols - 1] >= THRESHOLD_HIGH || cannypixels[rows * width + cols + 1] >= THRESHOLD_HIGH || cannypixels[(rows - 1) * width + cols] >= THRESHOLD_HIGH || cannypixels[(rows + 1) * width + cols] >= THRESHOLD_HIGH || cannypixels[(rows + 1) * width + cols - 1] >= THRESHOLD_HIGH || cannypixels[(rows - 1) * width + cols - 1] >= THRESHOLD_HIGH || cannypixels[(rows - 1) * width + cols + 1] >= THRESHOLD_HIGH || cannypixels[(rows + 1) * width + cols + 1] >= THRESHOLD_HIGH) temp = 255;
            else temp = 0;
            //temp = custom_canny.at<uint8_t>(rows, cols); //255;
        }

        temp_canny.at<uint8_t>(rows, cols) = temp;
        //printf("%d\t", ocv_canny_false.at<uint8_t>(rows, cols));
    }
    //printf("\n");
}

I'd be grateful for any ideas on what the problem might be.

Hi,

I'm currently working on replicating the Canny edge detector in OpenCV. I've managed to replicate the built-in Sobel operator using a 3x3 Gaussian filter and by calculating the magnitude as a weighted sum of absolute values of Gx and Gy (L2gradient is set to FALSE when calling Canny).

Sample outputs below:

original image:

OpenCV Sobel:

My Sobel operator:

My Sobel operator after non-max:

OpenCV Canny (L2gradient = FALSE):

My Canny ED:

I assume the problem is in thresholding. This is how I imagined doing it:

for (int rows = 1; rows < height-1; rows++)
{
    for (int cols = 1; cols < width-1; cols++)
    {
        temp = custom_canny.at<uint8_t>(rows, cols);

        //thresholding
        if (temp >= THRESHOLD_HIGH) temp = 255;
        else if (temp < THRESHOLD_LOW) temp = 0;

        else
        {
            if (cannypixels[rows * width + cols - 1] >= THRESHOLD_HIGH || cannypixels[rows * width + cols + 1] >= THRESHOLD_HIGH || cannypixels[(rows - 1) * width + cols] >= THRESHOLD_HIGH || cannypixels[(rows + 1) * width + cols] >= THRESHOLD_HIGH || cannypixels[(rows + 1) * width + cols - 1] >= THRESHOLD_HIGH || cannypixels[(rows - 1) * width + cols - 1] >= THRESHOLD_HIGH || cannypixels[(rows - 1) * width + cols + 1] >= THRESHOLD_HIGH || cannypixels[(rows + 1) * width + cols + 1] >= THRESHOLD_HIGH) temp = 255;
            else temp = 0;
            //temp = custom_canny.at<uint8_t>(rows, cols); //255;
        }

        temp_canny.at<uint8_t>(rows, cols) = temp;
        //printf("%d\t", ocv_canny_false.at<uint8_t>(rows, cols));
    }
    //printf("\n");
}

I'd be grateful for any ideas on what the problem might be.