27 – Understand How to Engrave Pictures – Part 1 (44:03)

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Welcome to another Lightblade Learning Lab, now today I’m going to attempt the

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impossible

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now you may laugh at this but I’m going to attempt to tell you virtually

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everything that I know about graphics and how we deal with graphics on this

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machine not I can hear you’re laughing because you think that I probably know

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about that much about graphics because I’ve purposely steered away from the

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subject up to now. We’ve talked a little bit about it and as you can see I can

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make a moderate attempt at getting a picture down onto a piece of material

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and I can show you quite a few more examples but that does not mean to say

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that I actually know what I’m doing that was a bit like shooting bullets in the

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dark yeah I fiddled around with a few parameters and I’ve got some reasonable

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results which is promising for you guys because it means you don’t need to know

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very much to get some sort of result but the problem there was I was having to

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fiddle around to get the parameters so I decided I will embark upon trying to

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understand what graphics was all about now I have documented all my mistakes

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all my learning processes that I went through to get the information that I’m

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going to pass on to you today if you want to go into great detail then you

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should spend sorry you might want to waste a bit of time and look here at my

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other video channel but to save you the tedium of doing that

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I’m going to attempt the impossible today and put something like about six hours

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worth of video into maybe three quarters of an hour

Transcript for How to Laser Engrave a Picture (Cont…)

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so sit back be patient and we’ll see what we can do to explain this

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subject to you in fairly simple terms in a way that you will fully understand what

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this machine can and cannot do in the way of graphics ok now I’m going to scan

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two images on this page and I’m going to give you a clue they’re both going to be

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scanned at the same speed and they’re both going to be scanned at the same

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power, power is about 4 watts coming out of the tube minus the efficiency of all

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the mirrors and the lens so there’s probably only about two and a half to

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three watts arriving at the paper surface here so it’s a piece of white card

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with two and a half watts going down onto the surface

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now what I want you to do is the usual powers of observation to see if you can

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determine the difference between scan one and scan two

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well, what do you think do they look any different?

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I think you’ll say the answer is no but believe me they are very different in

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the way in which the machine has produced them that’s what the whole of

Transcript for How to Laser Engrave a Picture (Cont…)

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this session is going to be about the difference between those two pieces of

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text that actually look the same but they’ve got completely different

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characteristics let’s go and have a look at what the

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program is that I used to send those two pieces of information down to the Laser

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machine. OK well here we are in RDWorks and you can see the two words text

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on the screen now if we look up here at the top right hand corner you’ll see

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that one of them is called BMP and the other is called nothing and that’s

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because that second piece of text has been produced like this 50 millimeters

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tall and I will change the font so that it doesn’t get confused with anything else

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and we’ll turn it into a script font of some sort there we go like that not very

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pretty but it demonstrates the point that I’m making when you create a piece

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of text in RDWorks it comes in as an outline font now that outline is

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basically a vector graphic outline and let’s just make it blue for a minute to

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demonstrate put it onto a blue layer now that blue layer can either be set as a

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scan layer which it is here or I can set it as a cut layer like that it doesn’t

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look any different the only difference is the machine will treat it differently

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this cut layer is exactly what it says if you cut that word text it will fall

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out and leave a hole in your material if we

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convert it to a scan layer as I said it looks no different at all but this time

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something different will happen now you can see the other two pieces down here

Transcript for How to Laser Engrave a Picture (Cont…)

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and there’s the big one at the top let’s just do a simulation and you will see

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what happens now it’s going to scan from the bottom and when it gets to this one

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it’s going to scan it lines across the page so the hollow text there basically

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means it’s uncommitted you can have it cut or you can have it scanned now what

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about the black text underneath well it’s come in as a bitmap you can’t

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change that because that’s all to do with how you produce the text outside

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this program and this piece of text has been produced in something like

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Photoshop or some other art package where you might produce your drawings

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and you import them into here as a bitmap or as a JPEG or a PNG or some

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other form of basically a bitmap type file in reality when I engrave these

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they both look the same but here as a text file as you can see it’s pretty

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blocky around the edge now I might be talking

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down to a lot of you guys but there’ll probably be people out there that do not

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understand what a bitmap is in relation to a vector file which is the text drawn

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above it okay well here we are close in on our two pieces of test text and I

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don’t think you can really see any raggedness around them around the edge of

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the bottom set of text it’s still pretty clean that is solid black text now

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although this is a very largely magnified part of a picture I think

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you’ll be able to see that there is an eye in that picture with a pupil and

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iris around the outside it is not a solid color it’s made up of lots of

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little pieces now those little pieces are called pixels and every one of those

Transcript for How to Laser Engrave a Picture (Cont…)

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pixels on that screen there is mapped with an x and y-coordinate

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so that the computer knows whether one pixel on the screen has got to be turned

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black or white so there’s a huge amount of data that the computer

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has to process to store a picture like this

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now let’s just go and take a look what I mean by pixels and this strange word

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called resolution the resolution of a picture is described in terms of PPI and

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I’m going to draw this one at 300 PPI pixels per inch now that’s the standard

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industry format for resolution and this particular picture is 300 PPI

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horizontally and it’s also 300 PPI vertically makes sense because they’re

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squares now when it comes to working in RDWorks most of you guys will have

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your machines set to work in millimeters if you’re one of the very few people in

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the world which probably includes America that uses inches still you will

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otherwise have to use millimeters what we need to do is to establish what the

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size of one of these pixels is okay now I’ve scribbled on this piece of paper

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here a very simple calculation that you can carry out that will enable you to

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convert from pixels per inch down to a size of a pixel so the first stage is to

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take 300 pixels per inch and divide it by 25.4 now there are 25 point four

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millimetres in an inch so what we’re really trying to do is to calculate the

Transcript for How to Laser Engrave a Picture (Cont…)

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number of pixels in a millimeter and the answer to that is eleven point eight one

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millimeters in a pixel so that’s pp millimeter pixels per millimeter now if

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we want to find out the size of a pixel if we know how many pixels there are in

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a millimeter if we divide the millimeter by eleven point eight one pixels it

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tells us that we’ve got 0.0847 millimeters

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is the size of that pixel there so that pixel there is 0.847

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millimeters square at some stage when you’re setting up your scan parameters

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you will be asked the question what is the increment and that will be asked

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for in millimeters that’s the answer to the question Oh

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eight four seven because you want to step down one pixel at a time in the

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y-direction Right now, the Machine cannot produce square shapes it doesn’t

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work in pixels per inch although pixels per inch is the thing

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that drives the machine what actually comes out of the nozzle are round dots

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you’ve seen it for yourself when you do a pulse burn down onto a piece of paper

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if you set the focus right you get the very very fine dot the machine works in

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dots per inch and the resolution of the picture that you’re trying to produce is

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in pixels per inch you would say yeah but the machine is going to

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automatically convert squares into dots as it runs across the page well you’re

Transcript for How to Laser Engrave a Picture (Cont…)

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absolutely right every one of these squares tells the machine to do

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something if we look at these pictures they do match up it decides whether it’s

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going to put down a black dot nothing a black dot nothing black dot black dot black dot

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now you might assume that that’s pretty logical most people don’t

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understand that the machine can and does work in dots when it’s using a bitmap as

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a driver I’m using that word a little bit carefully as a driver because there

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is another thing that can be used as a driver now I’m just going to draw two

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that look approximately like circles and this circle here is made up with pixels

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and this circle here is not made up with anything at all this is a vector because

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it has only got a ring around the outside and this one is a BMP it’s a circle made

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up of squares how the Machine sees a bitmap every time, every time it sees one

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of these pixels it sends out a pulse or not pulse or not not when we’ve got a

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black picture like this which is filled in it’s filled in with a series of black

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dots and it’s the collection of black dots that make the image look solid now

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that’s not the same when we’ve got the vector drawing the laser doesn’t go and

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put dots on here what it does it decides it’s going to scan backwards and

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forwards across this image like this and as it goes across it’ll draw a line with

Transcript for How to Laser Engrave a Picture (Cont…)

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the laser so we get a line that goes across there like that

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and then it comes back and we get another line and then we get another

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line we do not get dots we actually get lines that go backwards and forwards

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across the image like this now I’ve purposely drawn these as lines with big

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gaps between them but what you do this is where you set your increment and you

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can set your increment so that the lines join up and that then becomes a solid

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black shape as well but as you can see the mechanism by which the bitmap is

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produced and the vector shape is produced are completely different

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principles and that is a very very important thing that people do not know

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or understand it took me a long time to find out this difference this is a piece

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of perspex looking from the back of the perspex at

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an angle so that what we can see is a black rectangle that I had produced and

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the black, the black rectangle is obviously made up of every single dot in

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the bitmap and you can see those dots on here now when you look at it from the

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front it looks like a solid black shape but when you look at it from the back

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you can clearly see that that solid black shape has been made up by dots

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that join together now that is a very very important principle that you need

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to understand about producing graphics well we’re not really going to talk much

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more about this one because this one is very simple just lines and spacing

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increments this is the one that’s very very interesting to explore because if

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you want to put a photograph down onto a sheet of any material you will have to

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use a bitmap image to start with because that’s what photographs are the cleanest

Transcript for How to Laser Engrave a Picture (Cont…)

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way of producing a picture like this is probably to do it in Coreldraw and it

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may will then give you a DXF output so that you can produce a vector file which

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you can then engrave across and this is a nice simple way of producing block

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graphics logos text all the complications and difficulties come with

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doing something which is a bitmap and this is what I spent a huge amount of

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time, trying to understand this took me quite a long time to find out and I was

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quite staggered to find every dot in the bitmap can produce a signal for the

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laser beam to pulse this picture depends upon the size of the dot itself and the

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resolution of the picture now there are many different focal lengths of lenses

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that you can use in these machines the most common ones are one and a half inch,

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two inch, two and a half inch and four inch now

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every one of those lenses has something called a theoretical spot size now that

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is the smallest size dot you can produce with that lens and a two inch lens has

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got one which is a little bit bigger and a two and a half inch lens has got one

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that’s even bigger still and the 4 inch lens has got one that’s even bigger this

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is about 0.075 millimetres which in old money is point zero zero three, three

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thousandths of an inch and this one is point one zero zero which in old money

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is point zero zero four thousandths of an inch and so they go on and they get

Transcript for How to Laser Engrave a Picture (Cont…)

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bigger and bigger as the lens gets bigger this is probably the lens that

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most of you will have the Lightblade machine is fitted with one of these now

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in terms of size you can see that it is very very little difference now I don’t

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know whether you can see that but that’s two of my grey hairs there, that hasn’t

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helped my bald patch has it? The size of that hair is roughly point zero zero

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three, three thousandths of an inch or 0.075 millimetres so that just gives you

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an idea of just how small the spot size can be and this at point zero zero four

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you would not be able to see the difference between a 3 thou and a four thou

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hair so don’t get too concerned if you’ve got a two inch lens in your

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machine because it is not going to be a disaster when it comes to doing bitmap

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graphics it makes a big difference to the area the energy density you

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concentrate 60 watts into that size and then put 60 watts into that size the

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energy density there is almost well it is twice as high as it is in this one so

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in terms of cutting power this change makes a big difference

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but in terms of Engraving power it makes no difference at all

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okay now I’ve just drawn up a few little features on here having decided this was

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roughly the thickness of a human hair and we don’t have to worry about it in

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terms of resolution ability to produce a dot what we have got to worry about now

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is power because we can produce these dots at very very low powers but as soon

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as we start putting power into the dot the dot starts doing this gets bigger

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and bigger and bigger now that’s not what we want if we want fine resolution

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pictures we need the smallest dots that we can possibly get ultimately what

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we’re trying to achieve is a picture made up of dots different density areas

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just as you see them in a newspaper photograph if you look at it very

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closely you’ll see that is exactly that a series of dots and in fact we’ve

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already seen that today here’s how the eye can be fooled much much further away

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and you wouldn’t even see these dots you just see what looks like a photograph a

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grayscale photograph and that’s one of the magic tricks that that happens

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between the eye and the brain it has this ability to heal over all these

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little imperfections and produce a lovely picture for you to look at so we

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need the smallest dots we can get and to achieve that we really are looking for a

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small focal length lens and very low power now how does speed affect it? Well up

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to about a hundred millimeters a second the dots really don’t change too much

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away from Circular but if you start going 150 200, 300 and 400 millimeters a

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second then here’s what happens your dot turns into a sausage a short sausage and

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then the faster you go the longer the dot becomes but this black set of

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pictures that I’ve drawn here is not quite right because

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there’s another phenomenon that occurs in parallel with that now if you use a

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larger power to start with you get a bigger dot and if you start then

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increasing the speed of that larger power here’s what happens you get a

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sausage but the sausage is smaller than the dot and as you increase the speed

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the sausage gets narrower and narrower and so you get back much more towards

Transcript for How to Laser Engrave a Picture (Cont…)

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the original dot size here so consequently if we start looking at how

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these lines sausages now sit on this picture here bear in mind we get a pulse

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for every pixel these are dots but we’re still going to get a pulse here a pulse

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here and a pulse here so that means we’re going to get a dot there a dot

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there and a dot there the dots are going to start joining up and they’re no longer

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going to be seen as dots like that what we see is that now that looks much more

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like the vector scan but it isn’t because it’s still driven by dots and

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those dots that drive this are producing some really weird effects now it would

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be very very nice if we could produce dots and our picture look like this but

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when we actually burn dots into a piece of paper what we get is something like

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this now we’ve got brown dots slightly brown dots and lots of other different

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grades of brown dots in the background but hey if I was producing a proper dot

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graphic like this all these dots would look the same it would look like the

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measles they would all be nice and black and at the same quality

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the question is why are they all different shades of brown, different

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power the shade of brown tells us the amount of power that’s gone into the dot

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how much the paper has scorched when we’re doing dot graphics like this we

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have the power set to say eleven percent and eleven percent

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Max and min there should be no variation in the grade of the dots they should all

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be exactly the same little black dots but they’re not and the question is why

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not now just coming back to this, this was done fifty millimeters a second very

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slowly but it’s done with thirty percent power thirty-five or forty watts of

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power coming out of the tube and this is a resolution of 100 pixels per inch

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that’s what this picture was done at if we start going faster than that we lose

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our individual dots and we get lines where the sausages are all joined

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together so a hundred pixels per inch at 50 millimeters a second which enables us

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to produce this lovely pattern here single dots is what I would class almost

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as the Holy Grail that we’re looking for we’re looking for the ability to produce

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good clean single dots to try and get my measles effect that I call it you know

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we want nice uniform colored dots all over the picture so that we can produce

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the same sort of picture that we produce with an inkjet printer just two colors

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black and nothing so the background is left bare and every one of these little

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burns is exactly the same color now that’s what we’re aiming for and this

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looks as though it’s going to give us the parameters for achieving that so

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here we’ve got 100 pixels per inch divide that by twenty five point four

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means we’ve got three point nine four pixels per millimeter and so here we’ve

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got fifty millimeters per second as the speed that we’re running it so if we

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want to work out how long it takes for one millimetres worth of travel we take

Transcript for How to Laser Engrave a Picture (Cont…)

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one millimeter we divide it by 50 milli we divide it by

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50 and that basically gives us an answer of point zero two seconds per milliliter

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20 milliseconds if we now take the 20 milliseconds in other words that’s how

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much time it takes to travel a millimeter but we know that in a

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millimeter we’ve got three point nine four pixels so if we take the time it

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takes to travel one millimeter and divide it by the number of pixels in

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that millimeter we get approximately let’s just call that four for example

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four pixels per millimeter it’s nice simple calculation and we get

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approximately five milliseconds per pixel so that’s the amount of time that

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it takes to actually put one of these pulses down now if we start messing

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around with anything faster than 5 milli seconds per pixel then which will start

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producing something which is getting closer and closer to this so at the end

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of the day the crucial thing is how much time we’re spending putting a pixel down

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and that depends on the resolution of the picture and the speed at which we do

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it if we want to remain at 5 milliseconds per pixel which really is

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what I class is almost a golden number then we can either change the resolution

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of the picture from say a hundred pixels per inch to 150 pixels per inch now that

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we’re looking we can increase the resolution and make it a finer quality

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picture but to do so what we’ve got to do is we’ve got to reduce the speed for

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50 millimetres a second to 33 millimeters a second to allow the same

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amount of milliseconds per pixel consequently we could also do it the

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other way around we could make the picture much much coarser down to 50

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pixels per inch and then we could push the speed up to our hundred millimetres

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a second which would still give us five milliseconds per pixel what I’m going to

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do is to show you this information in a slightly

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different way so Just remember we’ve got five milliseconds that we calculated

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for 50 millimeters a second, a hundred PPI so for that resolution that’s how much time

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we have for every pixel now what you see here is a relative set of resolutions

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this is a hundred pixels per inch 150 300 and 600 PPI these are all drawn to

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scale and what that means is the pixel size for 100 PPI 0.25 4 millimeters it

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then drops to 0.169, 0.084 and 0.04, 0.04 is just over the thickness

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of a human hair for every pixel so just to keep that in perspective now what

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that means is as we’ve already seen at a hundred PPI we can calculate if we run

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this at 50 millimeters a second and every one of these is run at 50

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millimeters a second we’ve already calculated on the previous sheet that it

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takes 5.08 milliseconds for a Travis across one pixel now if we start halving

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or we go to 150 pixels per inch that changes to 3.39 milliseconds as

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opposed to 5 and when we get to 300 pixels per inch it’s down at one point

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six nine milliseconds and at 600 millimeters a second it’s down at 0.85

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milliseconds so we’re getting incredibly short periods of time allowed for every

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pixel now what I’m trying to illustrate with this drawing is that the time

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allowed for every pixel is getting less and less and less as you increase the

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resolution you might think you’re doing a great job of increasing the definition

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of your picture but what you’re actually doing is allowing less time for the

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laser beam to burn in one spot and therefore the color of the spot will be

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less dense now that’s true if you’re using

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something like white card or an organic material like wood leather but of course

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that won’t apply if you’re using glass or slate or granite or something like

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that we get a completely different effect so let’s stay with white paper

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card or wood where we get grades of brown depending on the power that we put

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into the dot now things are starting to get quite complicated because although

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I’ve broken this whole problem down into little individual elements like this

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they don’t actually and can’t actually exist like this in reality typical dot

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size for a two inch lens would be probably somewhere in the region of

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about point two in practice I know theoretically it should be point one of

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a millimeter but in practice when you start burning it you’ll find it very

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difficult to get much less than point two of a millimeter so therefore when we

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start looking at a point two millimeter pixel in here that’s what it looks like

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now at 50 millimeters a second we’re talking about using small amounts of

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power here by the way say eleven percent very very small amounts of power and we

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get that sized pixel the best one that we can get now if we carry on using

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eleven percent power and we move the resolution up to 150 PPI and we try and

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put the same pixel on there that’s what we’re going to get we’re going to get a

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dot that overlaps with the next dot and then when we try and do it at 300 we’re

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going to finish up with the same dot at the same dot but look what happens is

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covering more and more pixels but remember the machine is driven by the

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pixels so consequently what will happen is we shall get the first circle here to

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match the first pixel and then the second pixel will drive another dot and

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so we should get another dot here and then

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third pixel will drive yet another dot and look I think you can see very

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clearly that we’re getting dots overlapping on dots overlapping on dots

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so we’re getting multiple multiple multiple burns and the finer the

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resolution the more burns we get in X and of course then we start stepping

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down in Y so we need to get multiple burns in X and in Y we’ve got a few

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parameters that are getting mixed up here we’ve got the dot size which is

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remaining constant even though the resolution is getting smaller and

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smaller and finer so we’re getting more and more overlaps which technically

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means we probably could be getting more darker burn but of course counteracting

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the darker burn we’ve got the opposite effect and that is the fact we’re

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getting less time for each one of these burns

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so although we technically might have a darker burn because we’re getting

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multiple burns we’re getting substantially less power

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because there’s less time for the dot in one spot now you can’t second guess what

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the result of this is going to be I’m just telling you what the problem is

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that you’re facing what we should do is find out how these things affect a

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picture in the next session when we start building pictures at different

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resolutions but for the time being what I’m trying to do is to explain to you

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the problems that we’re going to face so that you can understand all the details

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associated with producing graphics now you can see that we’ve got less and less

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time here for our burn to take place but what we haven’t considered is whether

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the machine itself can operate this fast for putting a pixel down and so I’ve

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done some work on both of my machines to see how good they are at responding to a

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demand for a pulse from each one of these pixels and we know that this one

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works because there’s the picture and so I’ve done some more work at 50

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millimeters a second and 100 PPI with a different pattern and I’ll show you the

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results of that pattern what you’re seeing here is the penetration of the

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beam into a piece of perspex now this is looking at it from the back so that we

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can see the penetration into the perspex itself look you can see these little

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Peaks so we’re looking at this from the backside at about 45 degrees so that we

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can see the penetration and what I’ve done I’ve generated a pattern here which

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is basically one pixel and this was all done at a hundred pixels per inch the

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resolution so we’ve got one pixel and then we’ve got a four pixel gap two

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pixels for pixel gap three pixels and a four pixel gap and we did that all the

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way up to ten pixels and so that’s one two three four as it says on here I have

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the tenth one is missing what we find is that the rise time the time that it took

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for the beam to form that Green Line is virtually nothing this was nine pixels

Transcript for How to Laser Engrave a Picture (Cont…)

36:01

wide and what’s happened we’ve got some very strange effect taking place here

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and then once the beam switch is off at about here we’ve got this pink line

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which shows the decay of the beam the time that power actually takes to

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disappear and so you can see that that pattern is exactly the same on every one

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of these patterns here whether or not we’ve got one or nine pixel groups so

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the rise and fall times are very consistent now the reason I’m showing

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you this is because just one of these pixels that I’m showing you on here is

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this so these are the single pixels that we can see here these pixels here in the

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background are single pixels and they’re the same pixels as you see here now what

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I’m now going to do is to just try and explain

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what we see here with these funny shapes now on this pattern here I’ve just drawn

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at just a nominal pixel pattern the black pixel nothing black pixel nothing

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black black black nothing black black nothing black nothing black okay now what

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we’ve got here is a little picture of the beam switching on and off and that’s

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what that black pattern is in the background there that’s the maximum

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power that we could expect the beam to achieve and this is theoretically what

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we’re expecting to see we get a pulse here it is creating a black dot and then

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we get no pulse so we get nothing then we get another black pulse and so it

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runs and here where we’ve got a group of three we’ve got pulse pulse pulse we’ve

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already proved that and I keep coming back to this picture so you don’t forget

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it we’re driving this laser with individual pixel pulses and I’ll just

Transcript for How to Laser Engrave a Picture (Cont…)

38:08

remind you of this picture here Green is the beam on and pink is the beam

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switching off and you can see how much drag or how much lag delay time there is

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in switching the beam off the beam switches on and it never makes it to

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this maximum that we were trying to go for the maximum power why not well

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because it has to switch off and it takes a long time to switch off so

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therefore it starts switching off early and it never makes it to this maximum

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position and we can see that clearly on here look there is a one pixel there’s

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two pixels and two pixels joined together are higher than one pixel three

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pixels joined together are higher than two pixels four are higher than three

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but then that’s where we start to stabilize out once we get to four pixels

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we’ve achieved a uniform height so basically it takes almost four pixels to

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reach the ideal depth the maximum depth now I haven’t quite shown that on this

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diagram here but what we’ve got we’ve got

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a rise time and a fall then we’ve got nothing a rise time and a fall

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nothing then we’ve got a rise time and a fall but because we’ve got a pixel right

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next to it it doesn’t get a chance to fall right the way back to zero so

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consequently we rise again in the same time and we can climb the power a little

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bit higher towards the target that we’re aiming for and then it falls and it

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doesn’t drop down again as far and eventually after in this particular case

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I’ve drawn it three pixels I’ve reached the maximum so and then we drop down

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with two pixels we get to a different level with one pixel we get to this

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level so basically what I’m saying is if we’ve got one pixel we achieve this much

Transcript for How to Laser Engrave a Picture (Cont…)

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burn if we’ve got three pixels we can achieve this much burn and if we’ve got

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two pixels we can achieve this much burn now that’s a variable amount of burn

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depending on the grouping of the pixels it’s getting quite complicated the way

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in which all these factors are interacting together but the point I’m

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really making here is that this piece here is a constant so the amount of time

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it takes for the beam to go up to a target value it’s aiming to get to 11%

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remember but it never got to 11% because we didn’t give it enough time it had to

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switch off this is why I keep laboring the point about these times and

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milliseconds because 5 milliseconds here’s what the picture looks like now

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there’s only 3 milliseconds we would have even less time to go up and come

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down and goodness me look what happens at 0.85 milliseconds we get hardly a

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chance to start before we’ve got to stop so what I’m really saying is here the

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response time of the beam itself to turning its power on and turning its

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power off to different levels can have quite a significant effect on the amount

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of burn we get and the density of the burn that

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we get on these pictures and remember earlier I was saying to you I was trying

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to find an explanation why our dots were not all dark black well here we are

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we’ve got different groups of dots here which operate at different powers where

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we’ve got groups of three four and five dots up here we’ve got a dark burn but

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where we’ve only got single dots we’ve got hardly any burn at all and

41:58

then we may have double dots and triple dots that isn’t what I was expecting but

Transcript for How to Laser Engrave a Picture (Cont…)

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that’s what we’re going to get if we drive the resolution too high and if we

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run the speed too high remember the resolution is going to

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affect the time but of course this is at fifty millimeters a second so if I

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increase that to 100 millimeters a second I would have half as much time on

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each one of these and if I ran it at 200 millimeters a second I have a quarter

42:34

as much time so time is a most important factor because it’s all related to the

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response capability of the power supply and the laser tube to produce a sharp

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dot now that was hard work and I hope you’ve understood that it is the

42:55

explanation that I’m putting forward for this strange pattern of variable burns

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you will see in the next session when I start doing some real pictures how this effect

43:07

this strange effect which I’m calling pseudo grayscale because technically

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these should all be black all the same density but they’re not the same density

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so we’ve got degrees of grayness in here but we’re not using grayscale this is

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what I call a pseudo grayscale system well I’m going to leave you now where

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we started this session off that there being a filled vector piece of text and

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that being a bitmap piece of text now as I said to you they don’t look any

43:42

different but believe me I think after this session you can understand that

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they are done in a completely different way now this is a very simple exercise

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in the next session we shall deal with real photographs where I think you’ll be

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quite surprised at some of the results we get