OK, genius needed. Vector vs Raster

[Eric Allen]

A bit of background: I've been playing around with some zinc coated aluminum. I vectored some characters on it all the way down to 100s/1p/500ppi. Now my real question: Shouldn't raster at 600dpi, 100s, and 1power at least equal that for power? I tried it at 5 power and got no results at all in raster. Bumped to 20 and got strange results. The characters were numbers in different font sizes, so 1 was 1pt, 2 was 2pt, etc. up to 24pt. The material very lightly engraved down to 5pt being just barely visible, with visibility increasing up to 24pt fairly consistently which I attribute to the width change. I just can't help but wonder why 100/5/500 vector performs soooo much better than 100/5/600 raster, which in my way of thinking, should produce a very similar, possibly better result because there are more pulses in the second one.

[Mike Null]

I 'm afraid I might be at the wrong end of the genius scale but I believe you're dealing with two different speeds. On my machine the top vector speed is 31.5 inches per second but the raster speed is 140 inches per second. So a 5% setting on vector would yield about 1.6 ips while 5% on raster would yield 7 ips or more than 4 times the speed.

The variable I didn't address is the dpi as dpi is not a factor in vector engraving.

The other question is the material. I haven't previously known of anybody engraving zinc with a CO2 laser.

I would also be surprised if you can get a legible image with fonts smaller than 4.

[Eric Allen]

I mentioned the DPI/PPI because of the input of heat. I was wondering if the DPI would equate to PPI of the same amount. I was kind of wondering about dwell time too, that might be it. It seems to move very quickly through vector, but i can't tell what that equates to in raster. Seems like the zinc is going to require about the same settings as anodizing, it turns very white when engraved. It makes fantastic lines in vector, great for small tags and such with nearly no power.

[Mike Null]

Eric

I don't know if you have your owners manual but I believe that will point out the difference in ppi and dpi and they have no relationship. In reality I believe the dwell time would be the same for all dpi raster settings if the same speed setting were used. But, the higher the dpi setting the more spot overlap you get so might consider that increasing the dwell time.

For example, when I'm engraving maple, I almost always move to my highest dpi setting in order to effect a darker burn.

[Kenneth Hertzog]

Eric
I'm not sure if this will answer you question or help add to the convusion.
I do cad programing and Epilog will only cut vector with a DXF file. since the thickness of the line is only one pass VS rastor which is multi pass for the line thickness. I've done engraving from cad with vector cut and had no problem at all.
How'd I do :rolleyes:

ken

[Eric Allen]

Eric
I'm not sure if this will answer you question or help add to the convusion.
I do cad programing and Epilog will only cut vector with a DXF file. since the thickness of the line is only one pass VS rastor which is multi pass for the line thickness. I've done engraving from cad with vector cut and had no problem at all.
How'd I do :rolleyes:

ken

I think Mike addresses it pretty well from a theory standpoint. If the two were equal in power or dwell in a given area, it should come out the same. I suspect there is just a bit more time spent in one place vectoring, must run at a slower speed. It would be nice if someone knew the specs on the vector vs raster speed on these units, that would probably confirm my suspicion. I'm wondering, if you have that .DXF driver installed, does that affect the regular driver? I had some vectors I wanted to try from Allycad, just to see if it gets rid of a bit of the quarter effect on edges, I've been told that it's number of nodes that causes that, along with speed and freq.

[Kenneth Hertzog]

Eric
Yes I do have the vector driver installed and they are totally independant of each other. I've only used it with a DXF file can't say how other types of files would react.
ken

[Eric Allen]

I 'm afraid I might be at the wrong end of the genius scale but I believe you're dealing with two different speeds. On my machine the top vector speed is 31.5 inches per second but the raster speed is 140 inches per second. So a 5% setting on vector would yield about 1.6 ips while 5% on raster would yield 7 ips or more than 4 times the speed.

The variable I didn't address is the dpi as dpi is not a factor in vector engraving.

The other question is the material. I haven't previously known of anybody engraving zinc with a CO2 laser.

I would also be surprised if you can get a legible image with fonts smaller than 4.

I had to check out that font issue. So far:

100s/100p/600dpi Raster Nets a legible 2pt "2". No series at 100 speed I've tried gets much more than a stick with a blob for 1pt, which I suppose makes sense, given the spot size.

100s/5p/500ppi Vector nets a barely legible 3, haven't tried many permutations of this, might try 4/3/2/1 power just to see. Then of course there's ppi and speed affecting that, might be a little more clear with a lower speed and lower power, possibly a little variation of the ppi. Gotta get my color mapping laid out to maximum so this kind of experimental stuff can go quicker:)

I was right about the settings for anodized working in the end for raster. 100/40/600dpi makes some very nice pieces above 5pt, 4 needs 50p, everything lower really requires a lot more power.

[Darren Null]

*Hoping to be promoted to village idiot, but will give it a go*

PPI vs DPI
These are 2 different things; so trying to compare the 2 is an exercise in futility unless you make both values the same. The short version is that PPI deals with your image and how it's displayed. DPI is more to do with what your printer/etc is capable of. Better explanations:
http://www.tildefrugal.net/photo/dpi.php
http://photo.net/learn/resize/

Raster vs vector.
A raster (bitmap) image is a grid of pixels, each with intensity and colour information. A vector image is made of coordinates.

It could be that your laser is doing something like this for a horizontal line:

Vector:
>Go to start point
>Laser on at x power and speed
>Go to end point
>Laser off

Raster:
>Go to 1st dot
>Laser zap at x intensity
>Go to 2nd dot
>Laser zap at x intensity
>...etc

The second would take more in terms of back and forth to the control software (if that's how your machine deals with it), and that could be your speed issue.
The other thing to consider is that Raster images don't do lines, not really. Even if you have a raster hairline that looks OK; chances are that it's feathered into the image; which means that you have also to consider not just your line, but the pixels either side, which for a black line would be varying shades of grey to blend your line into the image for a smooth look. Your vector line is just that. Your raster line means that your laser will not just be drawing the line; but plinging away on either side of it too. Extra work (and more time) for the laser, and could also explain the legibility issue at extreme resolutions.

All just theories, of course.

[Dave Jones]

Actually Darren, the "PPI" he was talking about was not "Pixels Per Inch", which is what you are talking about. He's talking about "Pulses Per Inch" also known as "Frequency" in Epilog laser drivers. It's a high speed pulsing of the laser that happens when vectoring lines. Nothing to do with the PPI talked about in photography or graphics.

[Darren Null]

I sit corrected. Thank you. I've been grafiking since Photoshop v2, but am still a laser virgin.

The pulses per inch value would change with the laser speed setting, yes?

[Mike Null]

Darren

PPI will not change the speed setting nor will dpi. But a higher dpi setting will take longer to engrave (raster) due to the additional passes the head must make.

An overly simplified description of dpi would be to equate it to a ruler.

A ruler with 1/8" graduations might be equated to 300 dpi while a ruler with 1/16" could be 500 dpi and 1/64" graduation might be 1000 dpi. For purposes of example each graduation would represent a pass of the laser head in the X axis.