OpenCV
There are many useful functions in the OpenCV libraries. Since they are not embedded into the C++ programs, they will need to be accessed through libraries. Below is some simple code showing the libraries required and how certain information can be read. This is a good way to introduce a new user to OpenCV and some possibilities. For more information, go to OpenCV Tutorials.
The Mat file type is a matrices that stores the pixel information from the photo and then outputs it. A waitKey value is necessary. If it is 0, the photo will stay indefinitely until the file is closed. For videos, a waitKey of 30 inside a while loop is usually good. 30 would be 30 milliseconds, the time between each frame.
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//required libraries for OpenCV to access functions. hereon out, it will be the "usual libraries"
#include <opencv2/imgcodecs.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/imgproc.hpp>
#include <iostream>
using namespace cv; //allow for OpenCV variables
using namespace std; //allow for standard variables
void main()
{
string path = “test_image.jpg”; //can be jpg or png
Mat image = imread(path); //mat is matrix that is opened by open cv, data type is mat
imshow(“Image”, img);
waitKey(0); //system pause, not close until you close the file yourself
} |
Photo Functions
Some common functions for editing the photo include: black and white, canny. With that, you can dilate an image to decrease thickness and erode to increase the thickness of the lines. For instance, if there is a partial outline around a circle, then erode the image would make the partial outline thicker and possible connect the lines creating a circle. This will help enable better object identification. As well, the threshold function turns the image to black and white (1s and 0s) which makes it easier for object recognition.
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void main()
{
string path = “Resources/test.jpg”;
Mat image = imread(path);
Mat imagery;
cvtColor (img, imgGray, COLOR_BRG2GRAY);
//input, output
dilate(imgCanny, imgDil, imgErode);
//make kernel can be used by dilation
May kernel = getStructuringElement(MORPH, RECT, Size(5,5));
dilate (imgCanny, imgDil, kernel);
erode (imgDil,imgErode, kernel);
imshow(“Image Dilation”, imgDil); //make lines thicker
imshow(“Image Erosion”, imgErode); //decrease thickness
imshow(“Image”, img);
imshow(“Image Gray”, imgGray);
waitKey(0); //system pause, not close until you press close
} |
Shapes and Text
Below is an example of what you need to do for displaying a function. The key elements are the source file (img), points (centre, vertices) relative to the image coordinate system, the colour (scalar, use 0-255, 3 layer bit), and the thickness.
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void main()
{
//Blank image
Mat img (512,512, CV_8UC3, Scalar(255,0,0)) //0 to 255 8-bit
rectangle(img, Point(100,200), Point (382,286), Scalar(255,255,255),3);
circle(img, Point(256,256), 155, Scalar(0,69,255),10);//thickness, FILLED will fill
line(img, Point(130,296),Point(382,296), Scalar(255,255,255),2); //point is starting and ending point
putText(img, “John Doe”, Point(100,200), FONT_HERSHEY_DUPLEX, 1.5, Scalar(0,69,255),2);
imshow(“New Image”, img);
waitKey(0);
} |
Contributors:
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