14 – Photo Laser Engraving Myths

The Tangerine Tiger Series with Russ Sadler

In this Series, Russ has purchased a new 500 x 300mm, 50W laser machine from eBay with a view to modifying and upgrading it. In fact, he rips out the glass laser tube and high voltage power supply and replaces them with an RF laser source and PSU from Cloudray. This session is all about some of the more commonly believed Photo Laser Engraving Myths with an RF laser Source.

If you are considering purchasing a CO2 laser machine with an RF laser source from one of the big boy suppliers, I would suggest you check out this series before making a decision!

Contents

Claims to be able to burn 600 to 1000 ppi images with and RF laser engraver have always intrigued me. How is that possible when the technology uses the same laser beam and lenses as DC glass tube technology? There must be something magical happening when the beam pulses at high frequency! Not only can it produce dots thinner than a human hair, but DEEP and DARK images when the physics dictates this is not possible. Now that I have a puny 20-watt RF laser source I hope to discover the slight of hand tricks that are being used to convince us that there are holes in the laws of science.

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Photo Laser Engraving Myths: RF Laser Source Engraving a Photo
Photo Laser Engraving Myths: RF Laser Source Engraving a Photo

Transcript for Photo Laser Engraving Myths

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Well, welcome to another session with my tangerine tiger. A.

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Hey, you’re not looking at me. Stop. Oh, I can see what you’re looking at.

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There we go. Now you can concentrate on me. But the last session we dealt with comparisons between the ref and the glass tube,

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now the magic has disappeared for me because I was hoping to be able to make this a really fast photo engraving machine.

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But it turns out it’s never going to be able to do photo engraving.

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No proper photo engraving. Now, I know the big companies claim that they can do photo engraving,

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but what I’m going to do today is to sort of go through the fundamental principles of

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photo engraving and show you how they do it and how it’s not a proper photo engraving.

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Now I’ve watched a lot of their videos about photo engraving in the hope that maybe I’m missing some tricks.

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It only confirms what I believed all the way along. They don’t really understand what photo engraving is now.

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I know that sounds of arrogant. Please excuse me.

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But I spent a lot of time trying to understand how to get the best out of these

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machines to get this photo as close to photo engraving as I possibly can.

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And what they’re doing is not. It’s a compromise.

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So today we’re going to go through the principles and hopefully I’m going to persuade you that you’ll never really

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be able to do any successful photo or engraving with a laser unless this is where those with big ones really win.

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Let me rephrase that big pixels don’t mean a lot, big pictures do mean a lot.

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And so consequently, I’m going to go through the basic principles of graphic design, not only if you send my rather dodgy artwork.

Transcript for Photo Laser Engraving Myths (Cont…)

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I’m also not a graphic artist either, but I have had to learn quite a few of the skills and techniques that graphic artists have to go through.

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I still might get a few details wrong, but the essence of what I’m going to tell you is about correct.

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It’s a lot better than the magic, the mystery, the tricks,

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the mistruths and the myths that you’ll hear when you watch any of the big companies talking about photo engraving.

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So I watched a very long session recently, but the guy who was really talking a lot about the cameras,

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the need to produce a wonderful picture, high dpi.

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No cameras don’t produce deep eyes. Laser machines produce deep eyes.

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Cameras work with people eyes the same as monitors work with people eyes.

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It just shows you the level of I hate to use the word ignorance, but lack of knowledge is probably better to use.

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So hopefully at the end of this session, you might have a bit of a decent understanding about graphics and how you are never

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going to really succeed unless you use a few of my tricks with an RF machine.

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Who knows? Perhaps the big boys will rewrite their software based on some of the stuff that I’m going to tell you guys.

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So I’m hoping at the end of this session, we’ll be able to jump up to the machine and convert some of the images that I’m going

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to produce of this young lady into reality and just see what the end results are.

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Now, a couple of sessions ago, I tried to reproduce this image in a fairly basic form without any retouching or any modification to the picture,

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just straightforward conversion to grayscale and then to a digital image.

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They varied from abysmal to half decent.

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And we got to something that was pretty good, but not perfect by using some rather strange graphic techniques.

Transcript for Photo Laser Engraving Myths (Cont…)

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This looks like a very high resolution studio portrait picture, which it is.

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I mean, it’s great. The focus is on the eyes and the mouth and the teeth, and everything else is disappearing into the background except to fringe.

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But if we take a look at the properties of this picture, you’ll see that it’s got 162 megapixels at the top there.

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I want you to remember that number 162 megapixels. Bear in mind it says pixels per each p p i.

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That’s the number of pixels per inch that are on that image,

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and I want you to make a note that it’s roughly half a meter wide and three quarters of a meter tall.

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That picture, I know it isn’t on my screen, but that if you were to turn into reality, that’s what it would be.

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So I’m not going to change this picture to one pixels per inch.

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What do you think is going to happen? OK, Dave, go.

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You said hang up. That’s the same picture that had before.

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No, let me just show you. Image size.

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162 megapixels. Exactly what we had before, but this time, look at the size 256 meters wide and 234 meters tall.

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That is a huge billboard. Very big billboard at the point is that I change these pixels to one inch square.

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They don’t look one inch square, but that’s because a pixel can be whatever size you want it to be.

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You would have to view this from about a mile away to see that quality picture.

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And as you started walking towards this picture. You would see.

Transcript for Photo Laser Engraving Myths (Cont…)

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This sort of thing. Now, look, this is my one inch square pixels.

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That’s the first thing I need you to understand. A pixel can be whatever size you want it to be.

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The only problem is the bigger the Pixel,

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the further away you’ll have to be to see the quality of the picture that you’re producing with those pixels.

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OK, so let me do something else now to the standard size the Nets resample at this time and constrain the proportions.

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But this time what we do, we shall keep it at 300mm per inch and we will change the width to five millimeters.

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Yeah, I know it it on the screen and see what we’ve got now, that’s what you thought you were going to get the first time round.

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The point is here, as I tried to explain to you at the beginning, size does matter.

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We’ve still got 300 pixels per inch on this picture.

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But the picture is very, very small. So, whip, we’re using less pixels per element, so Fritz had her eye,

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if you take a look at our eye, it’s now only one two, three, four or five, about 10 pixels wide.

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So it’s a pretty crude picture because we have not got enough pixels to, if you like, give us all the detailed information that we’re looking for.

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Yeah, if you squint your eyes at that screen, your brain performs magic, and all of a sudden you can see the picture as clear as daylight.

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It’s only when you open your eyes and you can see the detail on the screen that you realize that, hey, this is not quite what it seems.

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So that’s the other important thing that I want you to remember, graphics is all about you falling your brain.

Transcript for Photo Laser Engraving Myths (Cont…)

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We’re not going to show you now is the basic technique by which the all the big companies approach this graphic problem.

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They’ve all got their own bits of software, or they’ll tell you to use this Photoshop or CorelDraw or CorelDraw,

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whichever you say tomatoes, tomatoes or you’ve got something like gimp.

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There are many bits of software which will perform the same tricks as those that I’m going to show you here in Photoshop.

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So the first thing that I’m going to do is I’m going to convert this image to something that the big boys say you should do, which is high resolution.

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You know, they claim that they can produce 600 or a thousand dpi images.

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Okay, let’s do it. File new. We’ll make our picture 180mm wide.

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We’re going to produce A4 size 180mm white, 250mm 250mm tall and a resolution of 600 pixels per inch.

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I’m not going to drag the image into here. Control minus.

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And then we do a shift key and drag one of the corners. To make it approximately the size that we want.

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We go then we just change tools to. Apply transform and then we’ll do view on screen.

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So there we go. So that’s now a 600 pixels per inch picture.

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It doesn’t look any different. The only difference that you would possibly see if we looked closely is there

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may be now in this picture at 300 pixels per inch on the right hand side.

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You may find that there may be a thousand pixels across her eye.

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Whereas on this picture, we may have 2000. So there are more pixels defining every element of the picture on the left hand side would not

Transcript for Photo Laser Engraving Myths (Cont…)

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change the information or the fidelity of that picture because we started off with a big picture,

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if you remember, which was 500 mm wide and 700 millimeters tall.

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We now change the picture to double the resolution from 300 to 600.

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But we’ve made the picture smaller, so we’re able to make our picture bigger with more pixels in it because we’ve decreased the picture size.

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Some of the videos that you see well spent a lot of time working on the colored picture to bring that,

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bring the color right to bring everything correct. Forget it.

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We’re not going to be working with color. What we’re going to work with as black and white,

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but as an intermediate stage between black and white, we’ve got to get to something called grayscale.

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We could at this stage go into the image and we could do image adjustments.

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And one of the very powerful image adjustment things is shadow and highlight.

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Well, okay, look, I could mess around these two to my heart’s content to try and bring out various aspects of it.

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But this is a very well-lit photograph, and I don’t need to play with this.

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So we should just do cancel and leave as it is if I zoom in on this.

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We can see we’ve got lots of different shades of gray in that image.

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Again, we can’t work with shades of gray on the laser machine.

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We’re going to burn some mark or whatever the material is.

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If it’s on slate, it might be gray. If it’s on acrylic, it might be white.

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If it’s glass, it’s going to be white. If it’s onto paper, it’s going to be brown.

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If it’s on the wood, it’s going to be brown. We’re going to get only one color to play with.

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It’s whatever the color is that we can burn onto the material we’re going to use.

Transcript for Photo Laser Engraving Myths (Cont…)

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So gray is no good to us at all. We’ve got to turn this into a binary picture.

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That means two colors the background color and the foreground color, and we do that by something called the dithering process image.

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Mode. Bitmap. Flatten the layers, this is where things get very interesting.

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Because. What I would normally do with this picture is to do something called a diffusion dither.

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We’ve already got 600 pixels per inch in the image. And so we say, OK.

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There we go.

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So that’s now a black and white image for those that you are not familiar with this, you’re going to say, but no, that’s a grayscale image.

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Cast your mind back to something I mentioned at the beginning of this video. Your brain is very, very good at telling you lies.

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Your eyes cannot see the detail in that picture, and therefore you are creating a false image of what that picture actually is.

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Let me zoom in and show you what that picture actually is. Those are pixels, 600 pixels per inch.

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And they are black and white. Black is what the light will burn.

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So that’s a set of Morse code signals to turn the laser on and off black being on a white being off.

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Now we talked about this before, but it’s no bad thing to reinforce it.

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Now you can see my little cursor moving around on that single pixel as it comes across from left to right.

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It’s going to hit that edge, turn the lights on, and as it turns, the lights are on.

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It will burn a dot. That’s all your laser can do.

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It can’t produce square shapes, it can only produce round shapes, so it’s going to turn on it at that moment.

Transcript for Photo Laser Engraving Myths (Cont…)

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It’s going to have half a burned dot hanging at the side of that pixel.

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And then it’s going to traverse across that pixel with the laser on, and then it gets the other end where White says, Okay, turn it off.

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But by the time it gets to that interface there Black-White interface,

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we’ve already got half the beam hanging out the other side of that pixel, although I’m calling for the computer to burn one pixel.

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Effectively, what it’s done is burn two pixels half before plus the pixel and half afterwards.

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Now, the problem with that is we’re going to fill some of the white that’s there.

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And so if we take a look at this picture before it, we’ve got half a pixel in front,

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half a pixel behind this one’s half a pixel in front and this one’s half a pixel behind.

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This one’s half a pixel in front. Look, it’s going to go black, black, black, black, black.

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Although the laser switch on off on off on the net result they’re going to get on material is black, black, black, black, black.

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And then we’re going to get black here.

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Oh, we’re going to get one and a half two pixels there, which are white, and then we’re going to get half out here, half here, half hour here.

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So we’re going to get a huge amount of black in here because we’ve got lots and lots of single pixels.

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Single pixels will effectively tell the laser to burn two pixels, so we’re not going to get the correct relationship between black and white.

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The relationship between black and white is the thing that is going to fool your eye into thinking that you are seeing a shade of gray.

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And as I zoom out, you will see there’s a huge amount of white in there that you can see.

Transcript for Photo Laser Engraving Myths (Cont…)

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Because that’s her face, that’s a shade, a very light shade. Whereas when you get to her nostrils, we’ve got a lot of black.

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Well, we’re not going to get a lot of black in that light area.

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We’re going to get a lot of black in that light area. So the picture is going to be very, very over burnt.

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Now the only way you can make that picture lighter is to lighten the image.

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To start with, let’s just show you what I mean. If I come back to here and I do my image adjustments.

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Brightness and contrast, no less to shadow and light. Net result was the same.

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So there we go. Look, we’re going to make that nice and light. This is one of the things that you’ll always be told when you work with an IRS machine.

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Yeah, we need to make this slightly lighter than normal.

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Why? Well, let’s just convert that picture, and I’ll show you what’s happened so effectively what we’ve done.

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We’ve lightened the picture to remove a lot of the black pixels so that those black

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pixels that do get turned from one to two pixels will not distort the picture too much.

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And we’ll bring the picture back to a more normal type of shade, whether you’re using a an RF laser or a normal laser.

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If you want to lighten your picture, generally, don’t just try and turn the power down because that won’t always work.

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Go back to your picture and make it slightly lighter. Reduce the number of black pixels in the image.

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I’m totally confident that the guys selling these machines, these RF machines,

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are tackling this photographic engraving problem completely the wrong way round number one.

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I don’t think they’ve taken into account the response time of their machines and the fact that the pixels are not one pixel, but two pixels.

Transcript for Photo Laser Engraving Myths (Cont…)

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So here we’ve got a table of typical focal length lenses.

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Now, most of the time, the lens that they will be using on their machines will be a standard two inch focal length lens.

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OK. Sometimes you’ll be able to get a one and a half each focal length lens.

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But hey, I and a half inch focal length lens is point zero zero three of an inch thousand seven inch three thousand seven inch.

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Now, in terms of millimeters, that is zero point zero seven five.

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Now, a two inch lens has a forto diameter footprint, as they call it, or spot size.

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And people assume that that spot size is supposedly the smallest spot that you’re going to be able to burn on your paper.

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It’s very much theoretical because I would like to somebody,

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I would like to see somebody burn a fourth out dot on a piece of wood or paper or card with

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a two inch lens and it for only to be point one or point zero zero four inches diameter.

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It’s almost certain it’s going to be around about.

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Double that. But zero zero, eight point zero zero six inches or anything from point one to zero point one five millimeters.

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OK, so what’s the importance of that?

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Well, let’s just stay with the theory at the moment and just let’s assume that we’re able to produce a point one dot.

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With a two inch lens, we’ve got this image here set to 600 600 pixels per inch.

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One each is twenty five point four millimeters.

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So if we divide that by 600, it will tell us what size each one of those pixels is.

Transcript for Photo Laser Engraving Myths (Cont…)

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And it happens to be. Zero for two.

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That’s less than point zero zero two inches.

173
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We’re going to produce dots. If they’re theoretically possible.

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Two and a half times the size of the pixels.

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If you look carefully at the top left hand corner, I’ve got a square that I’m moving around and that square is three pixels by three pixels.

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That’s the size of the dot that I’m going to be putting down.

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So let’s see that line of single pixels there. The first thing that happens is when the PC.

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When the computers start, it’s going to do that and then it’s going to move along to the next Pixel.

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And he’s going to do that, and then he’s going to move along to the next pixel and it’s going to do that.

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So all I’m going to do across there, I’m going to produce a three pixel line.

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I mean, it’s still going to take any notice that those black and white spots,

182
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I’m just going to produce a black line because I’ve told this to move down at 600 pixels per inch resolution.

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It’s going to move down one pixel.

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So it’s going to go back to the beginning and it’s going to move down one pixel and then it’s going to do the next line scan,

185
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scan, scan, oh, it might leave a little space there.

186
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Look, scan. Hmm. Fill that one up.

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Fill that one up. Fill that one up. So there we go.

188
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So we’ve got nearly two black lines now and then we’re going to move down another pixel.

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So how do you get the idea here? My. My dots are not the same size as the pixels.

Transcript for Photo Laser Engraving Myths (Cont…)

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So there is no point in making a high resolution picture that you can’t actually copy.

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The simple, very simple rule for good quality photo engraving is one pixel equals one dot or turn it on its head.

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One dot is the size of the dot that you can produce with your machine, with your lens on that material.

193
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You have to find out what that size is to start with, because if it happens to be, -.to you’ve got to set your picture to twenty five point four.

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Divided by point two millimeters equals 127 paper.

195
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I hope you’re getting the idea. No pixels can be as big of small as you want, but at the end of the day, you can’t copy pixels.

196
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You’ve got to make the pixels,

197
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see the size of the dot that you can produce with your machine so that that determines the resolution of the picture that you can reproduce.

198
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How do these guys get on with 600 dpi? How can they manage that?

199
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So let’s get back to our grayscale image. I’ll show you how an RF picture is normally composed in each mode bitmap.

200
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Now, when we get to this stage, Photoshop, along with lots of other packages, have got the choice.

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We’ve used diffusion data, which is a lovely random pattern of dots to simulate the grayscale effect that you see in this picture.

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There are many different types of data. Which will come on to later.

203
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But this is the one that is normally used for RF work.

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We’ve got it set to 600 pixels per inch,

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which we know that we can’t produce because we have to produce dots that are two and a half to three times the size of those pixels.

Transcript for Photo Laser Engraving Myths (Cont…)

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Right now here we’ve got a further stage. We can choose various numbers here lines per inch.

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You say, what on earth does that mean? Well, it’ll become obvious in a second. Let’s leave it at 25.

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I could make that 22 and a half, for example, and we’ll make the shape round.

209
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What is this guy talking about? This is another way in which you could produce a simulation of grayscale.

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Now, if you squint your eyes again, you’ll see that it looks like a perfectly normal grayscale picture.

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But then again, then again, it looks as though, you know we’re looking at it through a net cut.

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That’s not a bad description, actually, because if I start zooming in on that picture,

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what you’ll notice is that we got black dots and we got white dots.

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If you look carefully, you’ll see that whether they’re black dots on a white background or white dots on a black background.

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They vary in size. That’s absolutely ridiculous because we can’t produce different sized dots with our machine.

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All we can do is produce one size dot the best size dot that we can.

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We can make the dots bigger or smaller by changing the lens and by changing the focal distance,

218
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of course, but we can’t keep changing the focal distance to change the dot size.

219
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So let’s zoom in a little bit further and see actually what’s going on.

220
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Huh? So that’s actually what’s going on.

221
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Look, we’re producing blobs made up of pixels.

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So we’re no longer looking at single pixels, assuming a bit more.

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So now what we’ve got. We have no or very few single pixels.

Transcript for Photo Laser Engraving Myths (Cont…)

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So my double pixel problem tends to disappear.

225
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Well, it doesn’t disappear completely because I’m going to produce a dot that looks like that.

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And then I come to the other end and I’m going to produce it looks like that.

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And then when I come back from the other direction on there to produce a dot that looks like that, an adult looks like that.

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So my dots are actually going to get bigger by half a pixel.

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All the way. And they’re going to get multiple burns because, look, I’m not just clearing one pixel.

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I’ve got a pixel that’s three times taller. So when I come to the bottom here, I’m going to get that.

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So if you look at my big blob, that’s been where every pixel has probably been burnt three times.

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And it’s got an extra half a pixel hanging out the end and the top and the bottom.

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Yeah, it is going to affect the ratio of black and white, but not by the same huge amount that it does with a normal diffusion dithered picture.

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That is how they tend to get away with high resolution.

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It’s not really a high resolution picture, it’s it’s a polka dot picture which has been burnt many times,

236
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takes a long time to produce because every line,

237
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every pixel has to be burnt and it’s every pixel was burnt three times, at least even if I replicate that oversize blob all over this picture.

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It changes the relationship between black and white a bit.

239
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But again, we’ve got a lot more white in this picture.

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So if we were to slightly emphasize the lightness or brightness of the picture before we started with it, compensate for that.

Transcript for Photo Laser Engraving Myths (Cont…)

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I’m going to drop into a piece of software that I absolutely love.

242
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Although this doesn’t support RF tubes at the moment, it’s got a great set of graphics demonstration software in here,

243
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which will illustrate lots of great things about different sorts of dithering processes.

244
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Now here’s a young lady which has been imported as a color photograph, and it automatically strips away the color for us.

245
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Yeah. If we look at the parameters as of first of all, going to choose different sorts of dither here, the first one is called dither.

246
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This is very similar to the Floyd Steinberg death that I’ve been using in Photoshop, where it’s called diffusion dither.

247
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Okay. Nothing has changed because in this software you don’t mess around with the picture,

248
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but you can see the signals that are going to go down to the laser.

249
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By doing a preview now, I’m just amazed at the scroll the mouse, because that way I can get an enlarged image of it.

250
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It doesn’t have to get building. There we go. There’s a nice representation of what we’ve seen before.

251
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This is not exactly the same as the diffusion guitar because we’ve got lots of single lines here.

252
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Can you see that that’s going to be challenging for a glass tube, laser switching on and off that quickly?

253
00:29:14,960 –> 00:29:17,840
Everyone is virtually a single pixel by the look of it.

254
00:29:17,840 –> 00:29:23,210
Let’s just make sure we’re scrolling a bit further to see whether it’s not an aliasing pattern on the screen.

255
00:29:23,210 –> 00:29:28,430
No. Most of those are single pixels. Look, there are few doubles, but that’s it.

256
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So that’s what a did that pattern looks like in light.

257
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But which, to be honest, I wouldn’t use.

258
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So if I switch on, pass through here, then it will take whatever image I import and it won’t mess around with it.

259
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It’ll just output exactly the signal that comes from Photoshop.

260
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We take a look at something like Atkinson. So how does Atkinson work with this image at 600 dpi?

261
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A lot of. Long lines, again, everything seems to be broken up into little teeny weeny one and two dot pixels.

Transcript for Photo Laser Engraving Myths (Cont…)

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Let’s take a look at another one. These are all basically as you look at diffusion did this, but they run.

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They’re done with different algorithms. So let’s take a look to see what Jarvis looks like.

264
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Well, it’s a little bit more interesting. We’ve got a few long lines in there, but not many of them.

265
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Still, lots of single pixels and double pixels.

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By that, I mean, so we can see what pixel size is, because look, we’ve got a gap there, which is about half the width of the line.

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So that implies that we’ve got a pixel two pixels at a pixel three pixels pixel.

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Do you see what I mean? You could work out roughly what the pixel size is on here.

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Let’s take a look at this half tone. And there we go.

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You can recognize that now from the image at the bottom. So remember, every one of the end of those black lines is going to grow by a pixel.

271
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So it’s going to shrink the whites and every one of the blacks is going to shrink the whites as well because it’s going to grow longer.

272
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So whichever way you look at that, you’re going to decrease the white in the image.

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That means you’re going to have to overcompensate on the lightness before you try and do this dithering process.

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And of course, it gets worse than that because every one of these lines is going to be burnt two or three times.

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If we’re not careful, we could finish up with barbecue. That would be for a more powerful machine for my 20. machine.

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This may well work very well in terms of getting me some color because with a single dots process, I can’t get enough color to run at speed.

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So it’s very convenient to use this package to show you what the signals are that are going down to turn the lights on and off.

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So every editor has its own pattern, and it appears that the only realistic pattern for an RF is this blob pattern what they call half tone printing,

Transcript for Photo Laser Engraving Myths (Cont…)

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which is the original process used for producing newsprint. When you look at some of the videos of them producing images.

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They’re more like cartoons than photographs. Here I got an image that’s been produced by one of those pieces of RF dedicated software.

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I haven’t been given permission to use this photograph, so I’ve blanked out the face enough so that the guy is not recognizable.

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But what I want to do is to take a look and zoom in on some of the areas of this photograph.

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I mean, for instance, look, look at the beard, the texture of the beard.

284
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You mean you cannot see any hairs there. In fact, the texture of the beard looks exactly like the texture of the headband around the top.

285
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OK. Yeah, it’s a cartoon likeness, but it’s not a photographic reproduction.

286
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We can see all these funny shapes, these dots and blobs.

287
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So this is a 500 people image. There are very few single pixels on here.

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I mean, as I said, this is a very, very crude image and this is what I’m really saying to you.

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There is no way that you could class this as photo engraving. I rest my case.

290
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Now, that doesn’t mean to say this machine is not good.

291
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It’s certainly not suitable for the purpose that I thought I was going to be able to use it for.

292
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I’ve got the two images here, side by side. One is slightly different than the other.

293
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At this point in time. They’re both grayscale. This one’s got oblong pixels in it.

294
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And what I should do to this one is just simply image mode.

295
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Bitmap. Flatten the layers. Yes.

296
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254, which is the resolution I’m going to be using, because that’s the size dot that I know I can produce on the machine.

Transcript for Photo Laser Engraving Myths (Cont…)

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You have to go up to 300 or 350, depending on the line thickness speed they’ve got to use.

298
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But the line thickness or the dot size depends on the speed that I can run at, the faster I can run the smaller or with the dots.

299
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So it’s a bit of a bit of an experimental process.

300
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We’ve got to try and find out what size dots we can produce at the speed that we can produce a reasonably image.

301
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Now this is going to be done with a normal diffusion. Do now change this into a bitmap.

302
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So this time would change it to a half tone screen and 600 pie.

303
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OK. Now we use the numbers that we had before 25 pixels, 25 lines per inch, 22 and a half, and the shape is red.

Sorry, Captions end at this point due to excessive background noise..

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