使用 C++ (OpenCV) 刪除所有黑色像素並僅獲取所需的圖像

Question

我試過 findNonZero 和 boundingRect。 但沒有什么能幫助我。 我是 C++ OpenCV 的新手。 I did this using Python OpenCV which involved NumPy, but unfortunately I am not able to do the same in C++.

輸入圖像

Python：

def crop_with_arg(refactor_image):
  mask = refactor_image > 0
  coord = np.argwhere(mask)
  x0, y0 = coord.min(axis=0)
  x1, y1 = coord.max(axis=0) + 1
  cropped = refactor_image[x0:x1, y0:y1]
  return cropped

 def crop_image(image_crop, tol=50):
    mask = image_crop > tol
    return image_crop[np.ix_(mask.any(1), mask.any(0))]

 compressed_img = crop_with_arg(gray) 
 croppped_image = crop_image(compressed_img, tol=50)

我正在編寫目標 C++ 中的代碼，以獲得 iOS 的包裝器。

Answer 1

對於灰度圖像，以下代碼完美運行。

值 50 是可以根據已完成的預處理設置的閾值限制。

grayThres = gray > 50;
graycloned = grayThres.clone();
std::vector<cv::Point> nonBlackList;
nonBlackList.reserve(graycloned.rows*graycloned.cols);

for(int j=0; j<graycloned.rows; ++j)
    for(int i=0; i<graycloned.cols; ++i)
    {
        // if not black: add to the list
        if(graycloned.at<cv::Vec2b>(j,i) != cv::Vec2b(0,0))
        {
            nonBlackList.push_back(cv::Point(j,i));
        }
    }
// create bounding rect around those points
cv::Rect bb = cv::boundingRect(nonBlackList);
cv:: Mat returnImage = gray(bb);

Answer 2

我認為這樣的事情，使用cv::boundingRect()會非常有效：

#include <iostream>
#include <opencv2/opencv.hpp>

int
main(int argc,char*argv[])
{
    // Load image as greyscale
    cv::Mat im = cv::imread("thing.jpg", cv::IMREAD_GRAYSCALE);

    // Threshold image at 128
    cv::Mat thresh;
    cv::threshold(im, thresh, 128, 255, cv::THRESH_BINARY);

    // Do the actual work
    double t = (double)cv::getTickCount();
    cv::Rect ROI = cv::boundingRect(thresh);
    t = ((double)cv::getTickCount() - t)/cv::getTickFrequency(); 

    // Print timing and results
    std::cout << "Time: " << t*1000.0 << "ms" << std::endl;
    std::cout << ROI << std::endl;
}

樣品 Output

Time: 0.317279ms
[253 x 48 from (113, 503)]

---

順便說一句，您可以使用ImageMagick從命令行更簡單地執行此操作，它包含在大多數 Linux 發行版中，可用於 macOS 和 ZEDC9F0A5A5D57797BF68E37364743831

# Print coordinates of trim-box
convert thing.jpg -threshold 50% -format %@ info:
253x48+113+503

或者，實際上進行修剪：

convert thing.jpg -threshold 50% -trim result.jpg

關鍵詞: 圖像處理, OpenCV, C++, 修剪, 修剪框, 修剪框, 裁剪, 修剪框, 邊框, 邊框, 去除邊框, 修剪邊框, ROI, boundingRect(), cv::boundingRect()