Session 24 – Greyscale Photo Engraving with a Laser

The Concise RDWorks Learning Lab Series

Welcome to Module 3 of the new Concise RDWorks Learning Lab Series with Russ Sadler. Module 3 will build on the information learned in the previous modules and will be targeted on the differing types of laser engraving methods and the techniques needed to consistently achieve great engraving results. So let’s take a look at Greyscale Photo Engraving with a laser.

In this Session, Russ explains how he doesn’t really believe in laser grayscale photo engraving. However, some of the theory and practical aspects of achieving grayscale photo engraving will contribute towards what he considers to be proper photo engraving in the next video. Russ foes through the process to set up and run a grayscale photo engraving and explains why it is doomed to failure.

Release Date: 24th December 2021

Over the last 6 years, Russ has built up a formidable YouTube following for his RDWorks Learning Lab series which currently has over 200 videos.

The original RDWorks Learning Lab series on his “Sarbar Multimedia” YouTube Channel, follows Russ as he tries to make sense of his new Chinese laser machine and to sort out the truths, half truths and outright misleading information that is available on the web.

Six years later with over 4.5 million YouTube Views under his belt, Russ has become the go to resource for everything related to the Chinese CO2 laser machine user or wannabe user.

Greyscale photo engraving on a laser equals poor quality output
Desired Quality on the Left, Laser Greyscale Photo Engraving on the Right

In this new series, Russ has condensed his knowledge and experience of the last 6 years to provide valuable information and insights into the purchasing, understanding, use, repair and maintenance of the Chinese CO2 laser machines and their key component parts.

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Podcast Session 24 – Greyscale Photo Engraving

Video Resource Files for Greyscale Photo Engraving with a Laser

Compound Lens Focus Gauge

Dot Size Test Artwork

Greyscale Grid Artwork

Sample Dots Photo

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Transcript for Greyscale Photo Engraving with a Laser

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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. Nnow 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 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 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 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 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

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Last updated August 26, 2021

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