Session 24 – Greyscale Photo Engraving with a Laser

Transcript for Greyscale Photo Engraving with a Laser

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The Concise RDWorks Learning Lab with Russ Sadler.

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Session 24, Grayscale Photo Engraving. Well, as you can see, I’m in a very relaxed, maybe unenthusiastic, mood.

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Because today’s subject is something that I don’t really believe in, but I’m going to have to tell you anyway.

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Grayscale photo engraving. Really a total waste of time, but I’m going to have to tell you about it,

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because there are many other aspects of it which would be very useful information for you.

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The end result is really not worth my time for the next half an hour,

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but we’ll push on because it is a subject which will open us out into the more

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realistic subject which will come up in the next session or two, photo engraving,

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proper photo engraving, as I call it. And I will explain what I mean by proper photo engraving.

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And it’s not necessarily the same as what most people think of as photo engraving.

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So let’s see if I can work up enough enthusiasm to move and get started

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should we? Now in the last session we dealt with 3D engraving, OK, which was based on grayscale.

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How are we going to be able to use the same idea for photo engraving?

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The speed at which the scanning takes place and the speed at which the pixel power changes was quite phenomenal.

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But the problem with photo engraving is that we don’t want 3D’ness.

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We want a nice coloured surface to the material which produces a photographic image.

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Now, it would be nice if our photos would come out like this as 3D.

Transcript for Greyscale Photo Engraving with a Laser (Cont…)

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But if you remember, these are very specialist types of bitmaps.

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These are not ordinary photographs. These have been very carefully designed with colours in them which match the various profile heights.

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There is no such information in a normal photograph.

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So a photograph will have to be treated completely different when we come to put it onto the surface of a piece of organic material.

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Now, it only can be organic material because organic material is the only material which has got a color range.

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We can go from nothing, the background to something quite dark.

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So we got a colour range that we can work with. Now

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we’ll talk about that a little bit more later. So as we’ve already seen, if we put too much power in, we burn deep.

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We don’t need to burn deep for a photograph. What we’re trying to do is paint the surface with the different colours.

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We almost want you to tap dance on the point of a needle.

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It’s a near impossibility what we’re asking this process to do. Now,

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you will remember in the previous session, we talked about having a line, a scan line, running across our pixels.

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That was one pixel wide, and one pixel wide

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I talked about then 127 PPI pixels, per inch equals 0.2mm.

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That was fine for 3D engraving because, hey, you know, it it wasn’t very, it didn’t have to be very detailed.

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And despite the fact that I mentioned the caution that we had to take about making sure that our line was the right thickness,

Transcript for Greyscale Photo Engraving with a Laser (Cont…)

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we were running at the right speed, you know, did I take any notice of that?

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No, we just went in chose some numbers and did the 3D engraving.

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And just as I said, we got a result. So the parameters for 3D engraving don’t have to be too precise because it’s a fairly crude process.

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Not so with photo engraving. Typical photos that you see in a magazine will be around about 300 PPI. From a lot of experience,

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I can get pretty close to that standard at 254 PPI and that resolution we have a dot size of 0.1mm.

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Okay. Now I’ve invented a little test pattern that looks like this. Now

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it’s very, very special in that the pixels on this pattern are 254 PPI. In other words that line thickness there is 0.1,

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these pixels are 0.1.

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The gap between the pixels is 0.1.

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But it does enable me to very accurately assess the size of the dot that I’m able to produce with this machine.

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If my dots are like that. Then they point to dots because, hang on, it’s half a dot bigger and half a dot bigger and they touch.

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So these are 0.1 pixels. So that means I’ve got a 0.2 dot. Now

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that’s probably the best that you’re going to be able to achieve with your two inch lens.

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What are we going to do first of all, is we’re going to investigate in more detail, what we can do with the two inch lens.

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Just what sort of quality dot can we produce with that lens? What width of line,

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can we produce with that lens? Because, look, we’ve got lines here and dots here.

Transcript for Greyscale Photo Engraving with a Laser (Cont…)

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Both are equally important when it comes to dithered engraving, which is what we’re going to tackle in the next session.

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But in this session, we still need to make sure that we don’t go wider than naught point one for our line width.

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And we need to be able to make sure that the resolution of the dots is

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0.1. If we start working with wood, within that wood,

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we’ve got hundreds of other different sorts of wood that have all got different burning properties.

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Well, that’s going to be an absolute waste of time.

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If the material itself is going to change colour. We need a material which is going to remain constant so that when we change the power,

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we get a colour change, not when we change the material. So for that reason, I’ve chosen this card material.

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Now, this card material, as I may have mentioned before, is basically beer mat card.

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It’s wood pulp or in other words, it’s grainless wood.

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That’s the best example I can give you. It’s white. It’s nice to work with, but it’s consistent.

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That’s what we’re going to use for all our grayscale work. When I started my laser learning journey about six years ago,

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there were many enthusiasts out there with small machines that were busy doing grayscale photo engraving.

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The images were sort of coming out quite reasonable, I was moderately impressed with them at the time,

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but then I didn’t have anything else to compare them with.

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They spent absolutely ages trying to produce matrix patterns of various powers, burns and colours.

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But we’re not going to do that. We’re going to drop into this process with a little bit more logic and focus,

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because I want to get through it fairly quickly, because I don’t want to waste too much of my life on it.

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Well, here’s your two inch lens. We’re not cutting, we’re engraving.

Transcript for Greyscale Photo Engraving with a Laser (Cont…)

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And this is an engraving style of nozzle, short with a big hole in it.

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I’m just going to run my little dot test on this little test pad here so we can take it

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under the microscope and see it, because you’re not going to be able to see it here, although I have got something that I can examine it with.

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Okay, so we’re looking at these at 50 times magnification. From there to there is point two.

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So there should be a point one gap between here. If these dots are actually point one diameter?

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There’s a little teeny weeny bit of a gap which indicates the dots are a little bit less than point two.

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If they touch, they’re 0.2. Now, here I’ve got a scale which is point one.

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So if I move that across, so that dot there, which is typical of most of these dots, there’s one or two that are slightly smaller,

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looks to be around about 0.15mm wide, and that should be the thickness of the line on the dashes at the top of the page.

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Again, it’s about 0.15. So the dots and the dashes are about the same thickness.

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And the question is, do they look the same colour?

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Well, colour is a very deceiving thing because this blackness that we see here is not necessarily, burn.

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It’s obscuring the light. It’s black.

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That’s why we see a black hole.

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What you see on the outside of the hole here is a slightly tapered brown section where it has evaporated the material away.

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There’s some strange properties with lenses which I’m not going to explain the moment.

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But, in a very near future section, we need to talk about lenses because lenses have got some really strange properties.

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We have set this lens to the supposed manufacturers correct focal point.

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And we’ve set this at a speed of 250 millimetres a second.

Transcript for Greyscale Photo Engraving with a Laser (Cont…)

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And I’d like you to take a look at the, if you like, the shape around the outside, there.

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OK, you can see every one of these has got a burn, which is actually bigger than the little black hole in the middle itself.

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So when we come to look at the bottom line. These burns are definitely overlapping. 0.25, maybe even 0.3 nearly, diameter.

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They’re substantially bigger than the actual central core of burning, which has caused the hole.

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Now, in previous sessions, you’ve seen my diabolical diagrams, as my art teacher told me when I was young and at school, boy, take up plumbing.

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Yeah. He didn’t say, why don’t you take up brain surgery? Because, look, that’s what I’ve just performed here.

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I’ve managed to cut through one of those holes and get a section through it so we could see what’s inside one of those black holes.

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Is it black? Certainly isn’t.

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There’s a little bit of scorching, carbon around the top of the hole here, and you can see the depression around the top of the hole.

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But look what’s inside the hole. Just a little teeny weeny bit of brown scorching, nothing black.

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The point that I made to you was, what you’re seeing is an optical illusion.

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It’s not a black dot, it’s a black hole.

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And look, this is something that we thought we were just engraving on the surface.

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Look we’ve punched a hole, nearly one millimetre through that material.

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So here is the little bitmap pattern that I have been running.

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I’ve taken a little bit of a liberty with this. I’ve turned this into a sort of a grayscale pattern.

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Now, I know it’s not grayscale because it’s black and white. Ah, there’s the clue,

Transcript for Greyscale Photo Engraving with a Laser (Cont…)

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remember? White switches the tube on and off and switching the tube on or off delays the start of the signal.

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What I’ve done with this pattern, although you can’t see it, is I’ve changed the background from white (255) to nearly white (250).

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So at no stage in this pattern, will the beam switch off.

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So when I do a scan with this, what’s going to happen, it’s going to scan along here on off, on off, on off, it’s going to scan along here,

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nearly white, nearly white, nearly white, and then it’s going to go backwards and forwards until it hits this line and then it goes on, off, on, off.

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So it’s going to scan the whole of this pattern, right. Whereas previously what it would do, it would go zoom, zoom, zoom.

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Technically, we should see every one of these pixels this time, regardless of the speed at which we run,

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because the speed of light is substantially faster than this pattern can run.

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As I said at the beginning of this session, this is a pretty useless subject. A waste of my time in some ways, to get an end result, which is rubbish.

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But along the way, we shall touch on all sorts of rather interesting topics associated with the machine.

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And you will learn a lot more about the machine and the way in which the machine works.

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So this is one of those areas. The pattern that you’ve just seen, my dot pattern. Is two hundred and fifty four pixels per inch.

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That’s the resolution of that pattern, and it’s been purposely made that way.

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So we get naught point one millimetre square pixels.

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Now, if the pixels are naught point one millimetres wide, it means we get ten pixels per millimetre.

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And if we’re going to run this program at four hundred millimetres a second. What it means is we’re going to finish up with 4000 pixels per second.

Transcript for Greyscale Photo Engraving with a Laser (Cont…)

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OK, that’s 4000 on’s and 4000 off’s every second.

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To make these little dots. Now a thousand dots a second, basically means every dot is going to take one millisecond.

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So if we’re doing four thousand dots a second, it means we’re taking a quarter of a millisecond,

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which is actually 250 microseconds, 250 millionths of a second, per pulse. In terms of electronics,

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snail’s pace. This is not fast at all for electronics, 250 microseconds,

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so 400 millimeters, 400 millimeters a second and 254 pixels, per inch is chickenfeed.

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So we shouldn’t have any problem resolving these dots. Because we’ve pushed the speed up to 400 millimetres

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a second . I’ve increased the power now to 50 percent.

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Now, did you hear it going tssht tssht tssht? So it was scanning across

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all the time, and it just scanned one,

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2, 3 lines. That’s why it just didn’t go tssht tssht tssht as it did the first time we ever ran this pattern, because we’re running it in a different mode

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now. We’re going to keep it at a 100 millimetres a second, and I’ve dropped the power to twenty five percent.

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And now we need to go and look at those under the microscope. Now when I see information like this.

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I have to laugh out loud almost because, I will be saying something to my wife sometimes, and she would say, I know.

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As she says in such a way as though I shouldn’t have even asked the question.

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And then I’ll say to her, well, OK, what’s the speed of light in a vacuum?

Transcript for Greyscale Photo Engraving with a Laser (Cont…)

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Do I need to know? You know, she knows everything and actually knows nothing, but here’s an interesting point.

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One hundred eighty six thousand miles a second is the speed of light.

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Put it another way, it’s roughly 300 million meters a second. A second,

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everybody can visualize a second. Can you visualize or even count a millisecond? Even snapping your fingers takes longer than a millisecond?

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So when it comes to a millionth of a second, that’s becoming totally unimaginable.

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Now, if we take a thousandth of a millionth of a second, it becomes something called a nanosecond.

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That’s a billionth of a second. So if we strike all these noughts off, mathematically, what we’re left is one divided by three.

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Which means a third of a meter per nanosecond or a foot in a billionth of a second.

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That’s how far light travels. The way in which the laser beam is generated is by reflections backwards and forwards inside your

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one meter laser tube. Now some of that comes out the end of the tube and goes around the machine.

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Okay, so how big is your laser machine?

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Even right down at the front, right hand corner, furthest away from the tube, you’re probably no more than two meters.

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So the light traveling from the extreme end of one end of the tube is a meter another two meters around the front of the laser machine,

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and we’re talking about three meters. Well three meters, 10 times that, 10 nanoseconds.

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So 10 billionths of a second for the light wave to get from one end of the back end of the tube right down to your work.

Transcript for Greyscale Photo Engraving with a Laser (Cont…)

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It’s it’s unimaginably fast. You know, there’s nothing that’s going to beat it.

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Just a few moments ago, we spoke about how long it takes to generate this little teeny weeny pulse that I’ve got on my test pattern.

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And the answer was two hundred and fifty microseconds, as I pointed out at that time.

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Two hundred and fifty microseconds is like a lifetime in terms of the speed of light and the way

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in which the information is going to travel from one end of your tube down to your test pattern.

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That’s the reason why I wanted to go through this very interesting little piece of maths to show you that in physics terms, there isn’t a problem.

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We should easily be able to create dots at 400 millimetres a second or even a thousand

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millimetres a second if we can put enough power into the dot to damage the material.

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Remember the exposure time. So let’s take a look at some of the patterns that we produced,

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should we? Look we can see a dash there, with a gap.

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A dash there with a gap, another one there with a gap.

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And some really funny stuff here. And now let’s take a look at my line of dots along the bottom, my point one dots.

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Well, look, there is just a hint of the

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0.1 dots in there. Just a hint. But what on earth is going on?

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Why have I got a continuous line? Now we’ve slowed things right down to one hundred and fifty millimetres a second.

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These remember, are one pixel dots with three pixel gaps between them.

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But look, we might have one, maybe one and a half pixels gap between these dots.

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I wonder what happens to the bottom of dots? Ha ha ha What bottom row dots?

Transcript for Greyscale Photo Engraving with a Laser (Cont…)

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OK, now that’s a continuous line,

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but that’s because we’ve got a huge amount of power there and I changed the power to 100 millimetres a second and 20 percent power.

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What about our bottom row of dots? Ha ha ha. Well, there’s some hiding there in the background, but they’re still all joined up.

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OK, we just proved there is no response time from the physics.

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Why aren’t we seeing single dots with an instant turn on and an instant turn off.

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We should get beautifully crisp dots like this. The problem is, it is the physics getting in the way.

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I’m going to explain to you how that happens now. At the top of the picture there, you’ll see my cursor.

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Now, that’s not a cursor. That’s the laser beam. Look, I’m going to go “peep” and there’s a burn.

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Here’s my little pixel. Here’s my little burn dot. But the controller does not know the size of the dot.

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The controller only knows where the centre of the dot should be.

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Here it is, it’s moving the beam across this pattern and I’m doing it very slowly.

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And it gets to this point here where it reaches the centre of the beam and it says, OK, I’ve now reached the edge of a pixel, turn the power on – beep.

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And it continues the power on, all the way across the pixel until it reaches

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the other side of the pixel and when it reaches the other side of the pixel,

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it says, turn the beam off. Off, off, off, off.

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On, on, on, on, on, off.

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And there we go, what have we done? We’ve produced a two pixel wide dot for a one pixel wide signal.

Transcript for Greyscale Photo Engraving with a Laser (Cont…)

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Oh, dear. When we translate that into this bottom row here, I think you can probably anticipate what we’re going to see.

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We’re going to see half a pixel hanging out that side. And half a pixel hanging out that side.

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Half a pixel hanging out that side and half a pixel hanging out that side, et cetera, et cetera, et cetera.

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What have we drawn here? A continuous line. Purely because the beam is switching on so instantly,

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that it’s causing a problem. We’re getting a two dot burn for one pixel signal. Now without this pattern,

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youu would never see this problem,

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but it is an important detail to understanding how and why it’s nearly impossible to get good photo replication with a gray scale image.

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Because turning it to grayscale, we’re switching between two power levels and we still can’t get a clean signal.

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So it means that all our pixels are going to get effectively double burnt.

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So we’re going to get a very distorted photograph. It’s going to look very, very dark. Now

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it’s an interesting and fascinating problem that is all to do with grayscale engraving.

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And in fact, is exactly the same problem that we would have experienced when we did 3D engraving.

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But of course, with 3D engraving, we’re not after very, very fine detail as you are in a photograph.

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And therefore, if there was a little bit of smoothing between the various levels, you didn’t see it.

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So that’s why for 3D engraving,

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I didn’t bother to go through this exercise of determining what the line width was and what the pixel size was, et cetera, et cetera.

Transcript for Greyscale Photo Engraving with a Laser (Cont…)

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Because I knew from previous experience. When I put the beam out of focus, first of all, it’s going to make the line thicker.

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It’s going to make the pixels overlap. What the hell? Because hey, we’ve got serious overlap anyway, but it still worked.

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That’s the point. It still worked. Remember, I was using only 127 resolution on the 3D engraving, not 254.

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If you want a decent image, you’ve got to go to 254, which is a 0.1 pixel.

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Now we know we’re going to fail, but we’ll still push on and go through the process of trying to work out what we would do if we

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were ignorant enough to think that we were going to be able to produce superb results at the end.

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But in failing, we shall learn a lot. OK, let’s cut to the chase and get the pain over with shall we?

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Here is a very, very simple swatch, a grayscale swatch that I’ve designed.

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It runs from black and then we’ve got 60, 120, 180 and 240, not quite white.

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Remember, 255 is white, so this is nearly white.

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Now, what I’ve got to do now is to try and find some power settings and some speed settings that will sort of replicate that pattern.

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Maybe we’ll choose something like about four for our minimum power. Go much more than 30

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and I’m fairly confident I shall be putting some 3D’ness into it.

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Now, we know the resolution is point one because it’s 254 PPI.

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So we say, OK, and we’ll give this a try and see see what we finish up with.

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I’m just going to give you a quick introduction to something that I always use when I’m doing Photo engraving.

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It’s a little vacuum table I’ve made with some fans in here, and those fans suck air through and blow it out the bottom.

Transcript for Greyscale Photo Engraving with a Laser (Cont…)

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In addition, we’ve got one, two, three adjustable feet.

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Now, the point about a three point adjustment is you can set this table perfectly level.

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Now, I can’t guarantee that my metal plate here is that accurate.

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So whenever I do photo engraving, I always use this little table because it enables me to get perfect flatness.

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You do not want too much variation in the focal depth when you are playing with photographs.

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Now, when we come to using the vacuum table, next time I shall be setting the focus up with this very, very accurate slope gauge.

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Now I’m going to use that just for the moment, just to show you how I go about setting this table up.

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OK, now there’s a single point at the back. We leave that alone.

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We move to this extreme point here. I’ll set that to exactly 11 millimeters.

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Now I’ll move across to the other extreme point. It’s not quite eleven millimeters.

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It’s too high in that corner. So if I undo that corner, there we go.

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Exactly 11mm. Now I bring it across to this corner it’s 11mm and then I take it across to this corner and it’s 11mm.

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So you know I’ve got that to within naught point one of a millimetre over the whole of that surface. Now

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just for the purpose of my test square. I’m not going to put the vacuum on.

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We’ll just lie it on the top surface there knowing that it’s flat. Now I’veset my lens,

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twenty millimetres. Now when I look at these patterns, I feel across there, like that, it’s nothing.

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Just a small depression of some sort. Definitely 0.1 as I feel across the edges here.

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Point two? Maybe point three? This one is point three, maybe point four? Quick check.

Transcript for Greyscale Photo Engraving with a Laser (Cont…)

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Yeah, it’s about point four, so we’ve got some depth to that coloured cut and as you can see, if I rub it, it it changes colour a bit, because remember,

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we’re probably cutting into the surface and just scorching the top of the combs that I demonstrated to you in an earlier section.

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You can see now what’s happening. Look, I’ve only got to touch it.

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And I’m flaking the surface off. I’m drilling in deeper and I’m just leaving a brown surface, I’m not actually causing a colour change. Here,

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wasn’t bad at all. That was 30 percent. That’s 40 percent power.

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So 40 percent power is rubbish. So we haven’t got a wide range of colour.

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Dark brown

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to white. So it’s going to look a pretty mediocre picture because of the colour range, apart from the fact that the dots are going to be blurred.

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So here is a very demanding photograph which have already taken the colour out of.

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So it’s already transferred to grayscale.

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And as you can see, we’ve got black, black nostrils on a black nose and we’ve got all this detail around the eye, which is quite black.

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And we’ve got all this detailed fur hanging out the side here, with his whiskers.

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This is a very demanding photograph. So we’re going to try and do this on grayscale and then we shall use exactly the same

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photograph to do proper photo engraving in a later session so you can compare the two.

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So we’ll just go in and confirm, yes, we’ve got this set to grayscale. Image adjustments, levels, black, not too much of it white, a huge amount of it.

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Well, that’s because we’ve obviously got all this white around the outside here. You’ll note, it says level two five five.

Transcript for Greyscale Photo Engraving with a Laser (Cont…)

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Well, I’m going to do what I always do with pictures for grayscale, and that’s turn that to two five zero.

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So there is no white in that picture at all.

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Four hundred millimeters a second, four percent minimum power, 30 percent maximum power and a point one interval step.

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And we’ve got our output direct switched on.

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Now, in general, we don’t want fumes to run across the job after we’ve engraved it.

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So what we’d normally do when we’re doing engraving is instead of setting the start point at the corner here,

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you can either start at the bottom corner or I like to start in the middle because it means I can then centre my material much easier.

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So we go to config, system setting and I’ll change the start position to the bottom centre position.

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There’s our start position. I know that this file is a huge file and there is a specific problem with this laser machine.

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It cannot walk and talk at the same time. If I press start, it will immediately start trying to scan this picture.

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But at the same time it’s trying to download the picture and it don’t like that. At forty seven megabytes, which is what this picture is.

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It’s probably going to take maybe a quarter of an hour to send this picture down to the laser machine, but we’ll send it down and we’ll do download.

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Now I have a maximum of eight characters there, that I can put it. Well,

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maybe it’s not going to take a quarter of an hour, it might take five minutes.

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So I thought while the program is downloading what I’ll do, I’ll move the head to the correct start position, which is here.

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But listen, it’s complaining.

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It’s complaining because it’s downloading the program.

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There’s just not enough power in the computer that runs this machine to do two things at once. File download success.

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That didn’t take as long as I thought it was going to take. So now we shall have to go to the machine keyboard and select the correct file.

Transcript for Greyscale Photo Engraving with a Laser (Cont…)

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Now the file is loaded into the machine. I should be able to move around cleanly.

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Now we shall leave that cooking for about half an hour and then we’ll come back and see what we’ve produced.

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Well, if that was your first attempt at photo engraving, you’d probably say that’s pretty good.

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I’m very, very pleased with that. As I said, I was pretty impressed myself when I saw people’s first attempt at grayscale photo engraving.

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Just compare that to the original.

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There is no comparison, there’s nothing in the eyes, those eyes are dead, these eyes have got detail in it. Where are the whiskers?

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Here we’ve got a few little hairs showing up around the ears here.

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But we’ve got nothing of these whiskers, or these hairs showing down the side here or anything down here, it’s all disappeared.

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We’ve got a little bit of detail across here, but it’s nothing like the detail that’s in this picture. Now,

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this is an inkjet replication of the image that’s on the screen.

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And this is what you would class as a photo replication.

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This is inkjet dot per Pixel, and that’s what we’re trying to achieve with real photo engraving, which we’ll get onto in the next session.

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It’s okay, but it’s fuzzy. It’s weak.

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It’s rubbish. Let’s stop there shall we, before I get even more depressed.

Transcript for Greyscale Photo Engraving with a Laser