Automatically Cropping image using OpenCV

[DeepakHirapur]

Hi,

We are performing Auto Crop operations using OpenCV library in C# project, For few sample automatically cropping the image but for other samples It was not cropping properly.

Let us know anything is missing in source code.

Please find the below piece of code.

        `Mat image = new Mat();
        Microsoft.Win32.OpenFileDialog openFileDlg = new Microsoft.Win32.OpenFileDialog();
        Nullable<bool> result = openFileDlg.ShowDialog();
        if (result == true)
        {
            image = Cv2.ImRead(openFileDlg.FileName);
        }
        
        Mat GrayImage = new Mat();
        Cv2.CvtColor(image, GrayImage, ColorConversionCodes.BGR2GRAY);

        Mat BlurImage = new Mat();
        Cv2.GaussianBlur(GrayImage,BlurImage, new OpenCvSharp.Size(5,5),0);

        Mat CannyImage = new Mat();
        OpenCvSharp.Point[][] contours;
        HierarchyIndex[] hierarchy;
        Cv2.Canny(BlurImage, CannyImage, 80, 150,7);

        Cv2.ImShow("Original Image", image);
        Cv2.ImShow("Canny Edged Image", CannyImage);
        Cv2.DestroyAllWindows();
       
        Cv2.FindContours(CannyImage, out contours, out hierarchy,RetrievalModes.External, ContourApproximationModes.ApproxSimple);

        image.SaveImage(@"C:\Users\TestAccount\Documents\AutoCrop_OpenCV\Output03012022\20220103.jpeg");

        var contourIndex = 0;
        var previousArea = 0;
        var biggestContourRect = Cv2.BoundingRect(contours[0]);
        while ((contourIndex >= 0))
        {
            var contour = contours[contourIndex];

            var boundingRect = Cv2.BoundingRect(contour); //Find bounding rect for each contour
            var boundingRectArea = boundingRect.Width * boundingRect.Height;
            if (boundingRectArea > previousArea)
            {
                biggestContourRect = boundingRect;
                previousArea = boundingRectArea;
            }
            
            contourIndex = hierarchy[contourIndex].Next;
        }
        

        var finalImage = new Mat(image, biggestContourRect); //Crop the image
        string outputBaseDirectory = @"C:\Users\TestAccount\Documents\AutoCrop_OpenCV\Output03012022";
        finalImage.SaveImage(string.Format("{0}{1}{2}", outputBaseDirectory, "\\Output", System.IO.Path.GetFileName(openFileDlg.FileName)));
        Cv2.ImShow("Final Image", finalImage);`

[kuljeetsinhparmar]

Hii, I have found a alternative solution for this hope it helps

Suggestions:
Contour Area Filtering: Discard small or insignificant contours to avoid selecting irrelevant regions.

Use RetrievalModes.Tree for a full hierarchy.
Ensure that hierarchy relationships are processed correctly.

"csharp
Copy
Edit
contours = contours.Where(c => Cv2.ContourArea(c) > minContourArea).ToArray();
if (contours.Length == 0)
{
Console.WriteLine("No significant contours found.");
return;
}``