Transcript for Essential Graphics Techniques for your Laser
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The Concise RDWorks Learning Lab with Russ Sadler. Session 22: Essential Graphics.
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Now, today, we’re not going to go anywhere near the machine because the next three sessions that we’re going to be tackling are all about graphics,
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I’m going to make the assumption that some of you guys will not know anything about graphics at all.
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So I’m going to start from square one and I’m going to take you through the basics of graphics. In the same way that I’m not a physicist.
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I’m not a chemist. I’m equally unqualified to tell you much about graphic art,
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but I’ve had to understand enough about graphics to make sure that I’m moderately competent to get the best out of the laser machine itself.
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In the last session, we did some drawing work and that was using something called vector graphics.
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Now, without going too deeply into it. Vector Graphics is all based on mathematics.
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This picture on the screen here is not vector graphics. It’s something called a bitmap.
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Now, a bitmap is entirely different in its concept to vector graphics.
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I’m just going to add a grid. Now, that grid is not really what’s happening on the screen,
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but it enables me to explain roughly what a bitmap is. Now right at the top left hand corner there, you can probably see my cursor moving around.
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Imagine that square there to be something called a pixel.
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Well, every square on this screen is a pixel and every square on this screen has got a code.
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For instance, this is a bit like a spreadsheet in that this is column one.
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This is column two, this is column three, and this is row one, row two and row three,
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every single pixel on the screen has been defined by this mapping procedure.
Transcript for Essential Graphics Techniques for your Laser (Cont…)
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OK, so you can get to any single pixel on the screen by defining its position with coordinates
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as I’ve just described. These pixels that I’ve got on the screen here, this grid is is rubbish.
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It’s far too big, but it just basically explains the principle of a bitmap.
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Every one of these squares is mapped onto this monitor screen.
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So we take the grid off. So we just zoom in to her eye and now you can begin to see the pixels, the little squares that I was telling you about.
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There are millions of them. When I zoom out, you can’t see the pixels.
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First of all, your eyes are totally incapable of seeing those pixels.
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And that’s really the whole point of graphics these days with these little squares,
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these little pixels. We’re fooling the brain into thinking that there’s something there that there isn’t, that looks like a very high quality image.
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But as you saw when I zoomed in, it’s it’s made up of lots of little teeny weeny pieces.
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Now, the next thing to imagine is what is a pixel?
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Well, I’ve shown you what a pixel is, it’s a, it’s something that’s mapped onto the screen, something you can define by its coordinate positions.
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Let’s take a look at the properties of this image. I’m using an old version of Photoshop here.
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There is an alternative to Photoshop, which is free, and it’s a program called GIMP.
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There are a lot of tutorials to how to use GIMP, in the same way that there are a lot of tutorials on how to use Photoshop,
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Photoshop you hire by the month and GIMP is entirely free forever.
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The two programs are virtually the same in terms of their capability.
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So just because I’m using Photoshop doesn’t mean to say you have to go out and buy Photoshop to do the same sort of thing.
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Just go and download GIMP and there is all sorts of capability there for you to use for free.
Transcript for Essential Graphics Techniques for your Laser (Cont…)
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I’m going to take a look at the size of this picture. And here it tells me that, look, I’ve got an image which is 72 pixels per inch.
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72 pixels per inch is pretty crude in terms of a picture.
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Doesn’t look like a crude picture, does it? I’ll tell you what we’ll do.
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First of all, let’s take a look at the size of this picture. The size of this picture is
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ninety four centimetres, that’s nearly a meter tall and a meter wide.
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Well, it’s not on the screen, is it? It’s, it’s a very small image, but the pic, the picture itself is broken down into 72 pixels per inch.
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A pixel is whatever size you want it to be. So let me just change this resolution for a minute to one pixel per inch.
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Now, what are you expecting to see on the screen? One pixel per inch, OK?
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And there it is, one pixel by inch. But you say, “but nothing happened”.
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So that didn’t turn out exactly as you might have expected.
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The picture doesn’t appear to have changed, I’ve opened up the original picture here so that you can see how many pixels there are in this image.
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Twenty point five million pixels, two thousand seven hundred pixels wide and two thousand seven hundred pixels tall,
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which equates to a picture width of roughly a meter by a meter with a resolution of 72 pixels per inch.
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Now, the clue here, the very important clue is in pixels per inch.
Transcript for Essential Graphics Techniques for your Laser (Cont…)
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We’ve got 72 of them in this image, one inch divided by 72 defines the size of the pixel, so they’re pretty small pixels.
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OK, let’s go back again and change this to one pixel per inch and you’ll see that the picture is now 67 meters wide and sixty seven meters tall.
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Look at the number of pixels in the image, and it is still twenty point five million.
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We’ve still got two thousand six hundred and seventy seven pixels wide and tall.
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We haven’t changed any of the basic parameters of this picture, except we’ve made the pixels bigger.
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And in making the pixels bigger, we’ve actually created a huge image, sixty seven meters by sixty seven meters.
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And what this is equivalent to, you would see a high resolution image from a mile away.
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It’s a big billboard, but if you start walking towards this picture and you got to within a few feet of it,
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you would see the one inch square pixels that this image is made up from.
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You wouldn’t be able to see the image itself because at sixty seven meters tall and sixty seven meters wide.
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You’d be far too close to see it. So I hope you see from this example that pixels are not the thing that defines the quality of the picture.
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You can have a very large pixel provided it’s a very large picture.
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So that’s lesson number one, lesson number two from that,: Here we zoomed in on the eye.
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And if you look around the black section here, you can see the size of the pixels.
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Now, what I’d like to do is just guess at roughly how many pixels it takes from left to right of that picture, 300, 400 pixels.
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In other words, I’m able to break that image down into 400 discrete little pieces.
Transcript for Essential Graphics Techniques for your Laser (Cont…)
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And that will give me the detail of that eye.
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If I use less pixels, I will have less quality in the image.
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So bear in mind, these pixels are one inch square, but I haven’t lost the quality of the picture.
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So you expected this picture when I changed it to one inch pixels to be very blocky because you were expecting to see big pixels on the screen.
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So let me change the properties of this picture yet again.
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I’m going to leave the resolution at one pixel per inch and I’m going to change the size of the picture now. 67 meters down to five meters wide
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now. First of all, let’s go and have a look up here. We were twenty point five million pixels.
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We’re now down to one hundred and thirteen thousand pixels.
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How many pixels wide is this picture, 197 by 197 tall.
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Look what did we just say a few seconds ago. How many pixels does it require to define the eye?
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400, 500. Are you getting the idea? Let’s just change the picture.
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Looks OK at that distance, doesn’t it? Let’s put it on the screen and see what we’ve actually got. Hmm,
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I suppose if you squint your eyes, it’s not bad, but when you open your eyes,
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you can see the pixels and there are not enough pixels to clearly define that eye.
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Your eyes can actually detect the pixel resolution, and that’s not what you want.
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That’s the blocky picture that you were expecting.
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So the key lesson here is you need enough pixels in your image to resolve the smallest detail that you want to be able to see.
Transcript for Essential Graphics Techniques for your Laser (Cont…)
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It’s not the size of the pixel, the size of the pixels determines the ultimate size of your picture.
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It’s the number of pixels that will define the detail in your image.
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So when you can wrap your head around those two facts, you’ve got a pretty good idea how digital imaging works.
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Now, in this session I’m not really going to be relating any of this stuff to our machines.
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This is purely something that you need to understand about the philosophy of digital imaging.
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We will talk about how these philosophies apply to specific types of engraving when we venture into them in the next few sessions.
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Now, in the early days of photography, pictures were sepia coloured, they were brown, shades of brown,
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and in fact, that’s what we’re going to produce on our laser machine, probably shades of brown.
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So we’re going back to those old days long before photography was available.
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The printing press was around and they were making pamphlets, let’s call them newspapers, but they were news sheets of various sorts.
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But they could never use anything except drawings or etchings because there was no way to
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convert a photograph into the basic materials used for printing. White paper, black ink.
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That was it. OK, well, let’s just delve into that a little bit further
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should we? Let’s turn this into a black and white photograph by removing the colour.
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It’s not exactly a black and white photograph, but again, we’re being fooled by our brain and our eyes.
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Let’s look at the, let’s go and look at her eye and we’ll see what’s really going on.
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Now, we can clearly see the pixels in that image. And although this is a black and white photograph.
Transcript for Essential Graphics Techniques for your Laser (Cont…)
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It’s not made of black and white, it’s composed of black, white and shades of gray.
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Now, this is where something, which was invented with digital photography came along.
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Called the grayscale. And what it allows us to do, is to transform black and white photography into this very high quality digital photography.
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Based on something called a grayscale. And the grayscale is evident in this picture.
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We’ve got black, which is code zero and white, which is code 255.
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Now, that is a total of 256 colours, zero and 255 is 256.
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Now, the extreme colours are black and white and the two hundred and fifty four colours in between,
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if you want to call them colours, they’re actually shades of gray.
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They’re proportionate mixes of black and white.
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So that’s what the grayscale is.
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So the problem we’ve got is how do we get from this grayscale into something that can be replicated with just two colours, black and white?
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Well, here’s where we’re going to fool your eye and brain again. Here in Photoshop
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it’s called bitmap. But what we’re really doing is a process called dithering.
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We’re still using 72 pixels per inch. And we’re going to use something called a diffusion dither.
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Now, there are other techniques that you can use, but trust me, diffusion dither is the one that you want.
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This is based on a super algorithm called the Floyd Steinberg algorithm.
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And I’ll explain what that’s all about in a few seconds. But let me just magically convert this picture into black and white.
Transcript for Essential Graphics Techniques for your Laser (Cont…)
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OMG. That is abysmal.
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That doesn’t look like anything that you’d normally see in a newspaper.
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But that’s because we’ve got a very strange process going on here called aliasing.
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The pixels on my monitor screen are not the same pixels as in the picture.
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And so we’re getting a very strange sampling effect.
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If I change the size of that picture and just reduce it a little bit, I shall probably find somewhere.
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Not that one. But that one. It’s a place on my monitor screen that matches the pixels in the image.
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It’s a superb grayscale image. Let’s just zoom in and have a look at her eye again.
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That’s interesting, isn’t it? It’s just black and white, there’s no grey in there at all.
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But what we have got is white pixels and black pixels.
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But where you want dark colours, we’ve got less white and where we want light colours,
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we’ve got less black, the density of the black and white change to match the grayscale image.
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This is the clever algorithm that I mentioned, the Floyd Steinberg algorithm.
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There are several other algorithms around that try to do the same thing, but I personally have found that
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Floyd Steinberg in Photoshop. Or you’ll also find Floyd Steinberg mentioned in GIMP.
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It’s a superb algorithm for doing what we want to do, which is to convert grayscale into black and white for printing.
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As I said, we’re high jacking here with our machines a process that was not designed for laser machines.
Transcript for Essential Graphics Techniques for your Laser (Cont…)
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And this is where we will get into the processes later on.
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But if we can replicate these black dots with our machine, then we should be able to replicate this photograph. Hmm.
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That’s a fascinating prospect for a future session, isn’t it?
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Now, I hope that this has laid the groundwork for three sessions that we’re going to be dealing with in the very near future.
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One of them will be 3D engraving, which uses grayscale as the basis,
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then there is a way of converting the grayscale into various powers to try and achieve grayscale photo engraving.
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And finally, the pinnacle of this work will come when we try to do proper photo engraving using the dithering process.
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So between now and then, it might be a good idea if you download your own version of GIMP and start looking at some of
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the basic tutorials to try and emulate some of the stuff that I’ve done here in Photoshop.
Transcript for Essential Graphics Techniques for your Laser
