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  • so imagine that you're the victim of a burglary or the sum of the serious crime gone in in your neighborhood.

  • Then the police would come in and they search for different kinds of evidence.

  • Obviously, your boat was gonna be wearing shoes, so is gonna leave behind a shoeprint.

  • Currently, what they do is quite varied, So either they will They will get a suspect into custody and they will get them to stand on some kind of ink pad on, then stamp on a piece of paper.

  • This is a copy of my shoe print That was that was taken using this method.

  • So what I did was I stood on a on a vegetable, dye impregnated pad on, then stand or walk across this piece of paper.

  • What the police will be looking for is signs of where on a particular shoe.

  • So they can.

  • They can identify a shoot type quite readily from the from the tread pattern underneath.

  • It s so yes, they quite familiar with the different kinds of shoes that people wear, and they can classify them quite easily.

  • But it turns out that the way we wear our shoe down is actually quite specific towards, so we all have a slightly different gate.

  • We walk in slightly different ways.

  • Converse shoes, which are the ones that I'm wearing, are actually quite notorious for wearing in these kinds of regions underneath where the ball of the foot is a CZ you can imagine, so that the souls are actually fairly thin on what you see is you see distortion of these patterns in this kind of area as the shoot gets, although they also tend to where in this kind of area as well, so you can see quite specific things due to the individual.

  • The problem with acquiring images like this is that what they have to do is they have to take something like this and they scan it into a computer.

  • There can be quite a long period between actually acquiring an imaging on an image like this and actually uploading it to a national footwear database.

  • It's very similar to the kind of fingerprint databases that we're all familiar with from things like C.

  • S.

  • I.

  • The idea is that what they will be able to do is they'll be able to take Mark's acquired from crime scenes, upload them into this database.

  • Take Mark's acquired from people in custody and then try and match them.

  • So if you've got somebody who's been committing crimes around the country, all the different forces cannot blow these images, and you can search them against that and maybe placed people at different crime scenes the FBI expert and determine the make of a shoe on frequently.

  • Depending on the way that you were born, the vegetable ing thing can be quite smudgy.

  • There also may be a few compliance issues associated with getting people to do.

  • This is the wrong with any kind of evidence gathering process, but it's largely due to time.

  • Forensic service is have had their budgets slashed.

  • There's an increasing push to improve efficiency.

  • And you can imagine if you're somebody working in the custody suite on a Saturday night or a Friday night.

  • These are quite busy times.

  • You might not have time to process the evidence as quickly as you might like.

  • The conversation that we had with them was around the area of trying to acquire these images digitally in custody.

  • The idea being that you could you could get the person to stand on some device, you could acquire an image of the regions where their shoes contact a surface that could you press a button and not information.

  • Those images could be quickly uploaded to this national footwear database.

  • They could be searched almost immediately on.

  • Do you could make a decision as to whether or not to detain or release the way we decided to tackle.

  • This was actually using a fairly nice piece of physics, which is covered in most GCS.

  • See some buses.

  • So the approach that we've used is actually based on total internal reflection.

  • This is a piece of perspex on.

  • What we've done is we've wrapped thes led strips around the outside of it.

  • If I just plug this in so these led strips lights up.

  • Okay, so the led strips Okay, so the ladies run all the way up here on what we've done is we've wrapped them around the outside of this piece of perspex on.

  • Then what we've done is we've basically covered that up with, in this case, a piece of masking tape.

  • You can see me through this device.

  • Okay, So what's happening is the light's bouncing around and signed this so it's been total internal reflected inside this piece of Perspex.

  • But if I now bring something like my thumb into contact with the service of this than what you see is my thumb scatters quite a lot of white, and all of a sudden you can see the contact regions between my thumb on the piece of perspex.

  • So if I do it with my hand, for example, you can see a ll the regions where my my palm is touching up that piece of perspex.

  • So you can imagine if you did this with your shoe, you would see a similar kind of pattern.

  • And of course, if you were to walk across a new element like this than what you would see is that the intensity pattern would change and you would get a new image or a movie off the regions where your shoe is contacting this piece of post back.

  • So the idea is very simple.

  • Suppose we have something like a surface where on one side, we've got glass or plastic and then on the other side, we've got air.

  • Now, if we were to send in a beam of light towards that surface, we would see to things.

  • Firstly, we would see a reflected right reflected beam.

  • And if if we say that this angle of incidence is Peter I, then we would see the same angle on reflection.

  • So I'm gonna call that feature on, in this case, the Orion Theatre.

  • On the same, we'd see another thing as well, and that's a transmitted ray.

  • So we get reflected Ray and we get a refracted ray, and this refracts ID ray comes out at a slightly different angle feet to on that angle.

  • Feature to is bigger than the angle feta eye by virtue of the fact that the refractive indices of the air and the glass of different.

  • If we extend this idea and we make this angle of incidence bigger, what happens is that this angle feature to will continue to increase in size, and eventually what will happen is you'll end up with a situation where that ray will basically move parallel to that surface as we make this angle bigger.

  • So there's a critical angle at which this refracted ray will run across the interface.

  • Beyond that critical angle which this occurs, what will happen is the light will be totally in turn reflected All the light will be reflected back inside the glass block.

  • So this critical angle of incidence which will call theater, see, it's fairly easy to calculate if we know what the two refractive indices are.

  • So if we say that the refractive index off the glass, the plastic is end too, under the refractive index of the air is and one, then the sign of that critical angle is just gonna be equal to end.

  • One divided by into this is the condition where we don't have anything in contact with the with the glass or plastic that I talked about just now.

  • If we bring a contacting object in such as, Ah, a shoe sold What that does is it changes this condition.

  • And in these regions where I'm contacting the glass surface with the shoe, I now have a different refractive index given you end.

  • So I have a new and let's call it and three Okay, so now this condition, this kind of critical angle changes under the right conditions.

  • Light is no longer now totally internally reflected.

  • But some, like can actually escape on DDE.

  • He like, move into the sole of the shoe.

  • But that's do not do.

  • It is if that's if that she was also quite good Scatter of light.

  • So if if if the soul material scatters light, then what will happen is that some of that lie that goes in will actually be scattered back down in this direction.

  • So if we were to port a camera at the bottom, we could image these regions where the shoe was actually contacting the soul.

  • Okay, so this is Cinderella.

  • So this is the device that we've bean prototyping to use with the local police force on This is actually a device for imaging the shoeprints using the technique that I've just talked about.

  • What we've got here is a very, very similar design, but it's it's actually much larger.

  • We've got a big piece of acrylic Andi again, we've wrapped.

  • Led is around the outside of it.

  • I'm gonna zoom do now is I'm going to step up onto this thing, okay?

  • And so for now, because I'm in a lab, I'm gonna have to do something to try and remove the background.

  • Whiting, If you look at the screen now, you can see the regions where my shoes a contact in the surface that light up quite brightly in the same way that they did on the piece of acrylic that we were playing with earlier.

  • We can capture images like this on use them too.

  • Obtain a print of you like a copy of the contract regions where my where my shoe is actually touching this.

  • And this is the kind of thing that we would compare to a mark that we would find a crime scene so we can see As I move around, I get bright spots on dhe dark spots because of these images that we can see on the top left hand side, they're images that are produced by threshold ing.

  • These images that we saw when we were imaging just now.

  • So these are the kinds of things that you would compare to a mark that you would find a crime scene, and they look quite a lot like a fingerprint that you restored digitally for good reason.

  • Because the way they searched them is actually very similar to the way that they would search a fingerprint.

  • The images of the bottom here are provide complimentary information, so these are actually taken using conventional lighting on.

  • What they do is they just give us a photograph of the underside of the shoe on these useful because they also provide information.

  • That stuff that's perhaps not in contact, for example, that you've got something like a stone or a piece of glass embedded in the bottom of your shoe, which is not showing up in the contact regions, but which would make a difference if you were to make an impression in soft model.

  • So that again provide you with additional information.

  • If you're looking at a different kind of image, is that well, that looks like a keyhole, but they definitely can't get the key.

  • And there it is a pretend keyhole.

  • Okay, The weak point in all of these is the locking mechanisms.

  • So therefore you hide the lock so the key hole must be somewhere else.

  • Oh, hang on.

  • There's a panel here on top.

  • I literally just found this.

  • I wasn't pretending for the camera.

  • There we go.

  • Ha ha.

  • This is very scarce.

  • Is good is very ski.

  • Be.

so imagine that you're the victim of a burglary or the sum of the serious crime gone in in your neighborhood.

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B1 中級

鞋類鑑證--60個符號 (Footwear Forensics - Sixty Symbols)

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    林宜悉 發佈於 2021 年 01 月 14 日
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