Full Version: normal dpi output
From: Mike (MIKEHUNTER) [#10]
8 Apr 2007
To: Harvey only (HARVEY-ONLY) [#8] 8 Apr 2007
Harvey
Us poor Epilog owners only have the one setting.
Epilog's "dpi setting" is really lines per inch in the Y direction - I assume that this is what everyone is talking about.
At 600 "Epilog dpi", each pass overlaps the previous one by about 2/3 - this means that you get a good deep engrave. My own feeling is that this produces better results than "300 dpi" run more slowly.
From: Laser Image (LASER_IMAGE) [#11]
8 Apr 2007
To: Harvey only (HARVEY-ONLY) [#8] 8 Apr 2007
My laser works opposite of that - DPI is vertical pitch and PPI is horizontal. If I send a job out at 1000 PPI vs 100 PPI it takes the exact same amount of time. If I send a job out at 600 DPI vs 300 DPI it takes twice as long (or more).
I guess it depends on the driver as to what setting affects which axis of resolution.
Gary
From: Harvey only (HARVEY-ONLY) [#12]
8 Apr 2007
To: Mike (MIKEHUNTER) [#10] 10 Apr 2007
I had a nice long technical answer ready for posting, then accidentally closed the window.
It you have only one setting it is probably a 'square' setting, both DPI and LPI together. The ULS driver has them available separately, I almost always use it as a square setting anyway.
In your case 600 DPI will take twice as long to engrave than 300 DPI. Try both as a test and see if you think there is a difference in output. Some materials will show quite a difference, some (like wood) will not.
A laser spot is basically round. A .003 spot at 333 DPI will have the pulses touch only on the left/right and the up/down edges and leave 12.5% of the surface untouched. That is why overlap is necessary.
Also picture the edge of a row of touching circles, very uneven. Then superimpose that same row shifted 1/2 of a circle off center. A much smoother edge.
EDITED: 8 Apr 2007 by HARVEY-ONLY
From: Dave Jones (DAVERJ) [#13]
8 Apr 2007
To: Mike (MIKEHUNTER) [#10] 10 Apr 2007
From: Mike (MIKEHUNTER) [#14]
10 Apr 2007
To: Harvey only (HARVEY-ONLY) [#12] 11 Apr 2007
As I said above, the increased overlap at 600 "dpi" means that I get a deeper, better quality engrave than at 300, ***especially*** on wood.
It does take twice as long for a single pass, but when I was doing wood at 300, I would often have to do two passes to get the depth I wanted and still not get the quality.
I'm not convinced that the Epilog settings are "square". If I engrave anodised aluminium at 600 "dpi", I get definate gaps (lines) between the rows in the X direction. I don't see the same gaps in the Y direction. (This could be because of the laser on/off time (blurring the dots)). To get rid of the gaps, I always run aluminium at 1200 dpi, which gives excellent results.
From: Mike (MIKEN) [#15]
10 Apr 2007
To: Mike (MIKEHUNTER) [#14] 13 Apr 2007
Is there any chance you have a flucuation in your power supply?
From: Peck.Sidara (LAOPADAK) [#16]
11 Apr 2007
To: Mike (MIKEHUNTER) [#14] 13 Apr 2007
Mike,
The DPI setting used in the Epilog driver are square in that the overlap of pixels are in both the x and y-axis. It is something that is discussed in our current manual. There's a greyscale picture of a train engraved at both 300 & 600DPI showing the difference in quality. The difference is in both x and y. I believe it's more dependent on the material and file you're using when engraving whether you can clearly see the different for both x and y vs. just y.
Regards,
Peck Sidara
Epilog Laser
From: Dave Jones (DAVERJ) [#17]
11 Apr 2007
To: Mike (MIKEHUNTER) [#14] 13 Apr 2007
I've done tests on anodized aluminum at a number of resolutions and definitely see the X and Y both increase. For photos I do not send grayscale images directly to the laser when using aluminum. I always use Photograv to convert the photos to pure B&W dots first. Then all text and images are being sent already converted to pure B&W and I get more control over the result.
I've noticed with aluminum that when I set the driver to higher than 300dpi that the dots on the X change depending on the resolution of the image being engraved.
What I mean is that if I engrave a dithered 600dpi image at 600 dpi, or a 1200dpi image at 1200 that individual pixels in the X axis engrave too light, presumably because the firing of the laser is so short and it wasn't enough power to fully affect the anodize.
I find that setting the laser at twice the dpi of the original dithered image solves this since it fires the laser twice in the X axis for each pixel. I find that engraving a 300dpi image with the driver set to 600dpi gives me a good result. Alternately a 300 or 600dpi image engraved with the driver at 1200. But I don't see much change in those over the 300dpi engraved at 600, so that's the one I normally use.
When the image was not a direct division of the driver setting I got less predictable results. For example dithering an image to 400dpi and then engraving at 600 had a sort of beating to it and single pixels don't always engrave correctly on aluminum. Going to 1200 would of course be fine since the 400 is a direct division of 1200.
From: Harvey only (HARVEY-ONLY) [#18]
11 Apr 2007
To: Dave Jones (DAVERJ) [#17] 11 Apr 2007
From: Mike (MIKEHUNTER) [#19]
13 Apr 2007
To: ALL
Mike (MIKEN) - Thanks for the tip, but I don't think that I have a problem. The banding only shows up on aluminium and not any of the other materials that I do. I think that it is because the aluminium just soaks up any out-of-focus beam, so that only the centre of the focus point is engraving (in printing terms, I am seeing dot-loss instead of the more usual dot-gain).
I've not tried engraving a photo onto aluminium, though I would love to - all the ali I do belongs to my customers and it is all text and vector graphics.
One customer demands incredibly small text - 0.9mm (0.035") high - and it was quite a task finding settings which give good results on the fine stuff without blowing away normal sized text and logos.