Raster vs Vector

[David Somers]

I promise, this will be my last question for the night.


Throughout the forum I see reference to raster and vector on the lasers.


I understand the difference between the two forms in terms of graphics files; dots versus a mathematically defined line to over simplify it.


But, what is the difference on the laser and how it works. The discussions imply the laser treats the two graphics types very differently. How?


It seems like the laser is actually working in pulses. You can define the pulse timing. The speed of the carrier, the power of the beam, etc. But how does that get affected by a vector vs a raster file? Isn't the laser converting everything to raster because of how it operates….with pulses? Since there are obviously differences between how the laser uses these two files, what are the best, more common uses of them?


Lastly….are there some good books out there you might recommend that go into this kind of thing, and many of the other aspects of a laser engraver? I have to admit, even if I decide against doing this I am curious enough and interested enough about these things to take a stab at reading a book like that. Plus….if I don't actually buy a unit, I am likely to hire work out now and then and it would be nice to have a better understanding.


Thanks again everyone! And again….I promise. No more questions this evening!


Cheers!


Dave

[Robert Silvers]

Vector draws graphics primitives directly, like an old Asteroids video game. Raster draws an image out in grid line-by-line like an old tube television.

[Kev Williams]

Vector lasering is like drawing with a pencil. The laser follows a single line tool path.

Rastor lasering is like drawing with an inkjet printer. An inkjet printer's print head scans back and forth across the paper, laying down ink where it's supposed to and nothing where the page is blank. The paper moves up a small amount with each pass of the print head. Raster engraving is very much the same thing; the laser's lens (print head) scans back and forth across the work area, laying down pulsed laser light where it's supposed to, and the laser is off where ever the work is 'blank'. Where the paper moves in the printer, in the laser the gantry moves down in very small increments, typically 1/500 of an inch, aka 500 lines per inch.

Hopefully this picture (the lower part of which I drew using a hatch-fill routine so it's not entirely accurate) will help explain-- In vector mode, the laser would follow all of the outlines and single lines, nothing more, nothing less. In raster mode, the head will travel the entire horizontal path shown, from top to bottom (or vice versa on some machines), and the laser would fire only what I've drawn in red, which is WITHIN the outlines....

Hope that makes sense!
:)

http://www.engraver1.com/erase1/rastorvector.gif

[Michael Hunter]

The simplest explanation is that raster mode is used for engraving and vector mode for cutting.

The machines do treat these modes differently as Kev's post explains.

Vector mode *can* be used for engraving, by keeping the power below what is needed to cut right through.
Sometimes needed for very thin lines and/or details.

Raster mode cannot sensibly be used for cutting except for the thinnest materials which could be engraved all the way through at high speed.
Not easy to see a use for this, but it sometimes happens by accident with very thin plastic films.

[Martin Boekers]

I guess a confusing part may be that you can use raster mode for "vector images" such as fonts, as they are a vector outline with a fill. One thing to remember with vector pieces they are scalable with no loss of resolution as they are achieved mathematically.

[Robert Silvers]

I often outline my raster engraving with vector engraving.

[Kev Williams]

The term "vector" is thrown around rather loosely in the graphics world, to the point I don't know what "vector really means, EXCEPT concerning laser engravers! :)

I've noticed in sample videos, particularly with fiber lasers, that the operator will run a vector pass around the outline of a graphic before running the raster pass, the goal being to smooth the edges in the vertical plane and/or to highlight the edges. Myself, for my needs it's unnecessary, and a waste of time I don't have...

[David Somers]

Robert,


Thanks! As I mentioned, I understand raster and vector in the actual graphics files themselves, but I was missing how the laser itself was using them. That explanation was dandy!


Kev,


That diagram and explanation makes perfect sense. Thanks for taking the time to do that!!


Michael and Martin,


Thanks for adding yet more detail to this. Very helpful.


After all of your posts I went back and looked at some videos of jobs running and see now where something would appear to be running in a vector mode, where it was running in raster, and also where some things seem to be occurring in a hybrid mode for want of a better term. Kind of like Kev's description of a font being done with a vector outline and a raster fill.


You guys must get a bit weary of effusive thanks from newbies...but seriously...thanks for the time you have taken with these questions. The combined answers were very helpful and very appreciated and have given me a whole new range of things to pursue. If I can ever help you with woodturning or any of my other interests, just holler!

Dave

[Michele Welch]

Sorry to jack the thread, but I totally get the difference between raster and vector, what I'm not getting is vector engraving and how to use it to "fill" an area by utilizing vector engraving. Such as this example that you posted, You mentioned something about cross-hatch design, is that what I need to use to "fill" a shape so that it will vector engrave? If so, how do you do it? Thanks in advance for any answers you can give me.

Thanks,
Michele Welch
Very new laser owner still getting all the kinks out.


Vector lasering is like drawing with a pencil. The laser follows a single line tool path.

Rastor lasering is like drawing with an inkjet printer. An inkjet printer's print head scans back and forth across the paper, laying down ink where it's supposed to and nothing where the page is blank. The paper moves up a small amount with each pass of the print head. Raster engraving is very much the same thing; the laser's lens (print head) scans back and forth across the work area, laying down pulsed laser light where it's supposed to, and the laser is off where ever the work is 'blank'. Where the paper moves in the printer, in the laser the gantry moves down in very small increments, typically 1/500 of an inch, aka 500 lines per inch.

Hopefully this picture (the lower part of which I drew using a hatch-fill routine so it's not entirely accurate) will help explain-- In vector mode, the laser would follow all of the outlines and single lines, nothing more, nothing less. In raster mode, the head will travel the entire horizontal path shown, from top to bottom (or vice versa on some machines), and the laser would fire only what I've drawn in red, which is WITHIN the outlines....

Hope that makes sense!
:)

http://www.engraver1.com/erase1/rastorvector.gif

[Dave Sheldrake]

273600

The dark lines (wording like Union Pacific) on this train model are "Vector engraved" basically vector lines set at a low power/higher speed to "Mark" the material rather than "Cut" right through it.

cheers

Dave

[David Somers]

Michelle Welch!

Did you get your question answered? I missed your post in the thread and I am afraid I may have stepped on it accidentally and managed to distract people from your question. Pop it in again if you didnt get what you needed! And apologies if I accidentally distracted folks from you.

Dave

[Rodne Gold]

Easy answer , in vector mode the laser acts like a plotter , motion system wise and in raster mode it acts like a dot matrix printer , motion wise.
Some lasers pulse , some dont , some can vary the pulse timing when in vector mode so that you can get a perforated effect , the closer the pulses , the more like a solid line it is.T
he chinese ones don't have pulse settings you can change - tho do have other modes that allow less than solid lines when doing vector.

Outlining a rastered letter is hugely time consuming , you will see , especially on small lettering , the outlining will take 3-10x longer than the engraving and albeit it might "sharpen" the letter , the ramp effects where it has to slow for corners etc can also be problematic as the vectored outline varies in depth. You can often see this when doing acrylic , if you look at the acrylic sideways on , you can see the spikes drilling down into it.
The better way is to set your lasers tuning and backlash compensation so engraving lines up on the forward and backward stroke

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...-----
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...-----
BAD - fuzzy edge

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GOOD- sharp edged letter

To fill anything , it needs to be closed - a hole allows fill to "leak" - so a closed vector is a good "container"

To repeat , in terms of a vector fill , the vector is the thing that contains the fill and it has to be closed.

You can use various fill patterns , which are then seen by the laser as raster images and will engrave. Solid fills will engrave solid and patterned fills engrave as patterns

One would normally make the vector line invisible to the laser / laser driver unless you want the fill engraved and the vector cut or engraved as well

In some lasers , it identifies a VECTOR as a line with a certain colour or width
If you increase that width in , lets say , corel , the LASER does not see it as a vector and will engrave it
Corel will STILL see it as a closed vector item and will be able to fill it etc , regardless of its width or colour , it all boils down in this case , as to how your laser interprets a graphic as being vector or raster.

[Mike Null]

Michelle

Welcome to SMC.

One way to do a vector fill is by using the contour tool in CorelDraw. With some manipulation you can set the lines to fill your drawing. Complex drawings pose more of a problem and may best be done with a hatch fill which you can find in the post script fill tool.

[Mike Null]

David

Your work is precisely the kind of art that I wouldn't touch but I can understand infilling and inlay may in some cases enhance the work.

I have seen a number of turnings with silver and turquoise inlays.

[David Somers]

Mike, if I get to a point of trying some of this with a laser I will send you some photos and see what you think.

Dave

[Michele Welch]

Michelle

Welcome to SMC.

One way to do a vector fill is by using the contour tool in CorelDraw. With some manipulation you can set the lines to fill your drawing. Complex drawings pose more of a problem and may best be done with a hatch fill which you can find in the post script fill tool.



Thank you so much for your responses. My biggest problem, I think, is that I'm using Illustrator instead of CorelDraw. It's the program I know and I already have. Do you know what the hatch fill would be in Illustrator?

Thanks again and please be patient with me, I'm a newbie still and trying hard to understand everything.

Michele

[Mike Null]

Michelle

sorry, I have no idea.