5. OpenCV Tutorial - Learn Classic Computer Vision & Face Detection (OPTIONAL)/18. Blurring - The Many Ways We Can Blur Images & Why It's Important.srt

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So moving on to conclusions and bring that the first thing to notice that the convolution isn't and

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we can see the function Pizzi it's an actual mathematical operation once that's performed between two

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functions and it produces a function which is obviously an output coming out of the original operation.

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So this is sort of illustrated here.

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We have an image here.

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Then we run it by a function of convolution and our function has offices in kernel size.

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And what do we mean by kernel size.

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Well this really here represents a 10 by 10 image or pixel image here.

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And this is a 5 by 5 you know.

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So what this does here the convolution basically operates on one pixel at a time.

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So operating on this here of a pixel to do so deconvolution basically operates on this pixel but it

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takes into consideration all the pixels around it and its calculation you'll see why that's important.

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When we get introduced to blurring which is what we're about to do now so there is an operation which

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you obviously figured out that is an image so you can clearly see here.

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This is a shopping shift an elephant.

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I took a call just to do the zoo and this is the blurred image of the elephant.

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No actually she's not quite blurry.

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So this is an example of a matrix The Matrix is 25.

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Sorry five by five.

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Now we multiply meet the new matrix by one of the twenty five.

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And that's what we normalize that's called normalization of okeydoke Matrix because we want all the

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elements in this matrix to sum to one which I mentioned here.

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Now the first method I'm going to introduce you to is open see these filter Tuti takes an image and

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runs it past the kernel here.

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So we're about to introduce Saturno code.

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So let's go Tokuda and do so now.

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So let's look at this blurring of code here.

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We're going to use the open see the filter to see which is the most basic form of Pluton we can you

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do in if NCB.

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I'm going to do it by using a tree by treacle.

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Once you normalize by dividing by 9 so we're going to see the effects of blurring an image with a tree

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bettery you know and then beggaring it with a larger seven by seven canal.

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But you will also know all of these before dividing by 49.

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So let's run this one and take a look at it.

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In.

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This is our original image.

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You can see that elephant creases quite clear.

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So it's has a lot of detail in this image so that's run it by the tree by tree.

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And you can see it's definitely blue.

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It's not a substantial amount of Larry but it's definitely noticeable when you compare it to the original

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image.

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So let's take a look at the seven by seven.

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We expect a lot more heavy blurring and that's exactly what we see.

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This is probably what a person who needs high prescription glasses might see.

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So that's a fast learning algorithm.

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We're going to take a look at a couple of now

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writes If you scroll down over here you'll actually see some more blurring functions that are available

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in open C.v.

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So the first one we're going to use is actually a box filter.

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So it's called the CB2 to Blair function and it's an averaging filter.

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What it does it averages the pixels in a box that runs between each pixel.

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So it puts the input image here.

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Then it takes to really find here.

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This is a box size and averages on all the pixels here.

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So it sort of introduces a heavy blurring effect.

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It's actually quite quite a drastic learning effect which you will see shortly and that's why there's

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also the Gaussian blurring here.

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So what this does instead of having a uniform boxful to actually uses a Gaussian boxful to I'll show

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you what a Gaussian box is in a sleights.

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But for now just imagine it's not going to have such a harsh effect as this blue function.

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Now median blue medium blue also uses a box filter type I mentioned here.

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However it doesn't actually average out everything in the box.

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What it does it finds a median value of all that image all the pixels in that box and then it actually

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puts median value as a pixel.

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So it's sort of a nice balance between this and averaging.

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Sorry Dessen Gaussian.

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And lastly we have bilateral blurring bilateral blurring is actually quite useful.

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And what it does it actually preserves all strength it removes noise quite well and strengthens the

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edges in the image.

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So let's take a look at Rhonda squid and you'll see what I'm talking about.

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So this is an averaging box filter here you can see it has pretty much a uniform type effect.

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This is a Gaussian during here not to go blurring but actually the seams would actually be less blurry.

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But ever is a seven by seven in this example here.

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And this is a medium bearing here.

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Now if you notice medium bearing sort of has a kind of pinata type effect to it.

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And that's because it's finding the median value in those segments of the image.

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So if you wanted to ever introduce sort of a carpenter type effect maybe a medium medium blue would

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be quite useful.

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And let's take a look at our bilateral hearing here.

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Now as you can see an bilateral blurring it's actually sort of a anti losing type effect on this image.

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But what you can tell is that it definitely does preserve vertical and horizontal lines strongly here.

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But images of areas of the ears and different areas and the elephant is actually quite blue.

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However you can see vertical lines here are actually quite strong.

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So here's a slide summarizing to just those different types of blurring we just saw.

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So these are the same notes they just discussed here.

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On each of the four methods however I told you I'd show you what a gaussian kernel looks like and this

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is exactly what a Garcia-Pichel is here.

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So you remember previously before and other criminals everything was the same value here.

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However goshi and kernel's have a peak toward the center and is slowly peter off to the edges here.

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This is sort of a treaty representation of what a Gaussian looks like.

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And this is a matrix form here.

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And again we normalize by some of all the elements here which in this case is 273.

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So heading back to bite in the books is one last image Geering method to just wish to discuss.

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And that's one called imaged invoicing.

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This is open Zeevi function here first and one means the noise in code.

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It's quite a mouthful here.

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And what this does this actually originates from computational photography methods.

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And as you know using cell phone cameras and digital cameras there's no way those tiny camera sensors

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can match the noise levels of complex big DSL or cameras.

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So what they use to compensate is these complicated algorithms that sort of try to get the best optimized

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noise levels so you don't see all that green in the image.

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So when we run this function it actually takes some time of research on it in the background.

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You get this nice very clean looking image here.

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So that the effects of running this algorithm.

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Now there's quite a few variations here.

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I wouldn't get into the details exactly right now these are some notes on the premises here.

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This is filled the strings.

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And these are some of the components you can play with.

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And that's it for blurring.

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Let's move on to shopping which is the opposite of Barry.