1. What is the threshold operation?
We need to extract the part from one image, it should be compared with the gray value of each pixel of the image and a selected threshold value, and make the appropriate determination. (Note: Select the threshold value depending on the particular problem that is: there may be an object different gray scale values in the different images.)
2. thresholding type:
OpenCV provides threshold function: threshold () function . Function operates: The threshold value and the selected threshold value types, the pixel values of the upper and lower thresholds 255 set to 0 or to achieve effects binarization.
函数原型： void threshold（InputArray src,OutputArray dst,double thresh,double maxval,int type)
Parameters :
src: source image input
dst: an output image
thresh: threshold magnitude
maxval: maximum value of the fifth parameter
type:Thresholding type, Can be filled with digital numbers corresponding to 1-5 different types of thresholds:.
1.THRESH_BINARY
in the use of the threshold value type, the first to select a specific threshold amount, for example: 125, so that a new threshold value generating rules construed to be larger than the pixel 125 set to the maximum gradation value (e.g., 8-bit grayscale value 255 is the maximum), the grayscale pixel value is less than the gradation value 125 is set to 0.
2.THRESH_BINARY_INV
corresponds to the first threshold value of a type of inverted.
3.THRESH_TRUNC
likewise need to select a first threshold value, the image pixel is greater than the threshold value is set as the threshold value is less than the threshold remains unchanged. (Example: threshold of 125, 125 that is less than the threshold value does not change, the gradation value greater than 125 (230) on a pixel set as the threshold value).
4.THRESH_TOZERO
first select a threshold value, then the image processed as follows: gray value greater than 1 pixel without any change of the threshold value; 2 pixel grayscale values smaller than the threshold value, the gray values of all variants 0.
5.THRESH_TOZERO_INV
the fourth determination threshold value of the opposite types.
3. Foundation thresholding operation
Implementation code :
#include <opencv2/opencv.hpp>
#include<opencv2\imgproc\imgproc.hpp>
#include <iostream>
#include <math.h>
using namespace cv;
Mat src, gray_src, dst;
int threshold_value = 127;
int threshold_max = 255;
int type_value = 1;
int type_max = 4;
const char* output_title = "binary image";
void Threshold_Demo(int, void*);
int main(int argc, char** argv) {
src = imread("C:/Users/86159/Desktop/yasina.jpg");
namedWindow("input image", WINDOW_AUTOSIZE);
moveWindow("input image",50,0);
namedWindow(output_title, WINDOW_AUTOSIZE);
moveWindow(output_title, 800, 0);
imshow("input image", src);
createTrackbar("Threshold Value:", output_title, &threshold_value, threshold_max, Threshold_Demo); //创建阈值滑动条
createTrackbar("Type Value:", output_title, &type_value, type_max, Threshold_Demo);
Threshold_Demo(0, 0); //创建阈值化类型滑动条
waitKey(0);
return 0;
}
void Threshold_Demo(int, void*) {
cvtColor(src, gray_src, COLOR_BGR2GRAY);
threshold(src, dst, threshold_value, threshold_max, type_value); //阈值化函数
imshow(output_title, dst);
}
Results are as follows:
