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In this tutorial you will learn how to:
Everything looks familiar but the expression:
So, what does the function cv::putText do? In our example:
As a result, we will get (analagously to the other drawing functions) NUMBER texts over our image, in random locations.
Besides the function getTextSize (which gets the size of the argument text), the new operation we can observe is inside the foor 循环：
So, image2 is the subtraction of image and Scalar::all(i) . In fact, what happens here is that every pixel of image2 will be the result of subtracting every pixel of image minus the value of i (remember that for each pixel we are considering three values such as R, G and B, so each of them will be affected)
Also remember that the subtraction operation always performs internally a saturate operation, which means that the result obtained will always be inside the allowed range (no negative and between 0 and 255 for our example).
As you just saw in the Code section, the program will sequentially execute diverse drawing functions, which will produce:
First a random set of NUMBER lines will appear on screen such as it can be seen in this screenshot:
Now some ellipses will appear, each of them with random position, size, thickness and arc length:
Now, polylines with 03 segments will appear on screen, again in random configurations.
The last geometric figure to appear: circles!
And the big end (which by the way expresses a big truth too):