C# combined with OpenCV (6) Threshold segmentation-global threshold and local threshold

threshold segmentation

- src: input image, only single-channel images can be input, usually grayscale images

- dst: output graph

- thresh: threshold

- maxval: When the pixel value exceeds the threshold (or is less than the threshold, depending on the type), the value assigned

- type: type of binary operation, including the following 5 types: cv2.THRESH_BINARY; cv2.THRESH_BINARY_INV; cv2.THRESH_TRUNC; cv2.THRESH_TOZERO; cv2.THRESH_TOZERO_INV

- cv2.THRESH_BINARY takes maxval (maximum value) for the part exceeding the threshold, otherwise takes 0

- cv2.THRESH_BINARY_INV Inversion of THRESH_BINARY

- cv2.THRESH_TRUNC The part greater than the threshold is set to the threshold, otherwise it remains unchanged

- cv2.THRESH_TOZERO The part greater than the threshold is not changed, otherwise it is set to 0

- cv2.THRESH_TOZERO_INV Inversion of THRESH_TOZERO

Threshold: global threshold

Fixed threshold vs. automatic threshold

AdaptiveThreshold: local threshold

Local mean binarization and local Gaussian binarization

 public static void thresoldforexample()
        {
            var Src_Images = Cv2.ImRead("lenna.png");
            Cv2.CvtColor(Src_Images, Src_Images,ColorConversionCodes.BGR2GRAY);
            var Dstimage = new Mat();
            //0-Binary 超过thresh阈值置位maxval 否则为0
            //1-BinaryInv  与Binary 相反翻转 超过设置为0 否则为maxval
            //2-Trunc 大于阈值部分设为阈值，否则不变
            //3-Tozero 大于阈值部分不改变，否则设为0
            //4-TozeroInv Tozero翻转  大于阈值设置为0 其余部分不改变
            //8-OTSU 自动阈值
            Cv2.Threshold(Src_Images, Dstimage, 100, 255, ThresholdTypes.Binary);

            //var Dstimage2 = new Mat();
            //Cv2.InRange(Src_Images,100,200, Dstimage);

            var Dstimage1 = new Mat();
            //MeanC 阈值是邻近区域的平均值减去常数C
            //GaussianC  阈值是邻近区域的高斯加强总和减去常数C    
            //blocksize 邻近像素的大小，可理解为矩阵。           
            Cv2.AdaptiveThreshold(Src_Images, Dstimage1, 255, AdaptiveThresholdTypes.MeanC,ThresholdTypes.Binary,5,10);

            Cv2.ImShow("1", Src_Images);
            Cv2.ImShow("2", Dstimage);
            Cv2.ImShow("3", Dstimage1);
        }

 

 

Dual Threshold - Similar to Halcon. Select the grayscale value between two values

 var Dstimage = new Mat();
 //双阈值模式
 Cv2.InRange(Src_Images,100,200, Dstimage);