5. OpenCV Tutorial - Learn Classic Computer Vision & Face Detection (OPTIONAL)/12. Rotations - How To Spin Your Image Around And Do Horizontal Flipping.srt

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So let's talk a bit about rotations now rotations.

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Pretty simple as well.

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HOLOVATY also more Quick's that I'll teach you quickly.

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So using a favorite politician again Donald Trump issued exactly what a rotation is.

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So as you can see it rotates about a point and this point here in this image is the center.

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And just to set the image around that point so imagine that point as a pivot.

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So similarly in no translation transformation.

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We had a matrix.

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Now we have an M matrix which is the shorthand used for the rotation matrix.

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Here is the angle of rotation.

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As you can see it's an anti-clockwise angle measured from this point here.

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And one important thing to note is that the open Sivy function which is get tradition which is 2D actually

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does scaling an irritation at the same time which you will see in the code.

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So let's implement some mortician's using open C-v superstitions are very similar to translations in

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that we actually have to generate a transformation matrix.

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What we call the rotation matrix here and to do that we actually use an open CB function called Get

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a rotation matrix 2d.

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Now this function is fairly simple as well.

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What you give it is this argument is sense of x and y Center which corresponds to width and height that's

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the center point of the image.

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In most cases however you can and you are free to retaliate among among any point in image for whatever

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reason that maybe this is a theater which is an angle of addition.

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Remember it's anti-clockwise and this is a scaling factor which will bring or bring up shortly.

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And we use this rotation matrix again and it happens if you walk a fine function.

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So let's run this could see what it looks like.

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There we go.

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So that's that image rotated 90 degrees anti-clockwise and you may have noticed that a top and bottom

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parts of the image are cropped mainly because the canvas séjour means a seam.

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So there are two ways we can fix that one.

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Let's adjust the scale here.

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So let's put this point five wiggle.

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However it is a lot of black space around this image.

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Now to avoid that you would actually have to actually put the specific width and height of the new rotated

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image.

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So whatever you anticipate it to be you can program it here.

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However that's not often what is not.

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It's a bit tedious to do sometimes unless you have a special case for it.

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There's another way we can do it and that's by using the transpose function here not the transpose function

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that's run the school and see what happens.

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This is actually transposes image 100 percent.

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No you may not see the bottom because it's cut off from the screen casting off here.

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Over that image is fully done and here anti-clockwise and there's no black space around it.

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So this is just another easy and convenient way for teaching images.

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However when he does it in 90 degrees increments at one time so he can play around with us and actually

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do some cool rotations without having to actually program it with a new with a new height of the new

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canvas.