Writing very small characters on top of image OpenCV? - c++

Question

So Im trying to write a single character using putText() on top of an image to fit into a 25x25 box but the text is too small to render, it just looks like a blob of whatever color I choose the text to be. Is there any way to create small, readable text to overlay onto an image with OpenCV?

Answer 1

Here is an example using both putText() and also loading a character from a file created in Photoshop or GIMP.
#include <iostream>
#include <opencv2/opencv.hpp>
#include <string>
using namespace cv;
using namespace std;
int
main(int argc,char*argv[])
{
// Make a 3 channel image
cv::Mat main(200,300,CV_8UC3);
// Fill entire image with magenta
main = cv::Scalar(255,0,255);
// Load a character "M" from a file and overlay
Mat txt = cv::imread("M.png",-CV_LOAD_IMAGE_ANYDEPTH);
txt.copyTo(main(cv::Rect(80,120,txt.cols,txt.rows)));
// Now use puttext() to do a white S
int fontFace = FONT_HERSHEY_COMPLEX_SMALL;
double fontScale=1.5;
string text="S";
putText(main,"S",Point(60,100),fontFace,fontScale,Scalar(255,255,255));
// Save to disk
imwrite("result.png",main);
}
Here's the M.png file:
Here's the result:
I also notice that the anti-aliased fonts (on the right side in image below) look somewhat easier to read:
#include <iostream>
#include <opencv2/opencv.hpp>
#include <string>
using namespace cv;
using namespace std;
int
main(int argc,char*argv[])
{
// Make a 3 channel image
cv::Mat main(280,800,CV_8UC3);
// Fill entire image with magenta
main = cv::Scalar(255,0,255);
double fontScale=1.5;
int thickness=1;
int x=10,y=40;
putText(main,"Simplex",Point(x,y),CV_FONT_HERSHEY_SIMPLEX,fontScale,Scalar(255,255,255),thickness,8);
putText(main,"Simplex AA",Point(x+400,y),CV_FONT_HERSHEY_SIMPLEX,fontScale,Scalar(255,255,255),thickness,CV_AA);
y+=40;
putText(main,"Plain",Point(x,y),CV_FONT_HERSHEY_PLAIN,fontScale,Scalar(255,255,255),thickness,8);
putText(main,"Plain AA",Point(x+400,y),CV_FONT_HERSHEY_PLAIN,fontScale,Scalar(255,255,255),thickness,CV_AA);
y+=40;
putText(main,"Duplex",Point(x,y),CV_FONT_HERSHEY_DUPLEX,fontScale,Scalar(255,255,255),thickness,8);
putText(main,"Duplex AA",Point(x+400,y),CV_FONT_HERSHEY_DUPLEX,fontScale,Scalar(255,255,255),thickness,CV_AA);
y+=40;
putText(main,"Complex",Point(x,y),CV_FONT_HERSHEY_COMPLEX,fontScale,Scalar(255,255,255),thickness,8);
putText(main,"Complex AA",Point(x+400,y),CV_FONT_HERSHEY_COMPLEX,fontScale,Scalar(255,255,255),thickness,CV_AA);
y+=40;
putText(main,"Triplex",Point(x,y),CV_FONT_HERSHEY_TRIPLEX,fontScale,Scalar(255,255,255),thickness,8);
putText(main,"Triplex AA",Point(x+400,y),CV_FONT_HERSHEY_TRIPLEX,fontScale,Scalar(255,255,255),thickness,CV_AA);
y+=40;
putText(main,"Script",Point(x,y),CV_FONT_HERSHEY_SCRIPT_SIMPLEX,fontScale,Scalar(255,255,255),thickness,8);
putText(main,"Script AA",Point(x+400,y),CV_FONT_HERSHEY_SCRIPT_SIMPLEX,fontScale,Scalar(255,255,255),thickness,CV_AA);
// Save to disk
imwrite("result.png",main);
}