DPI verses PPI

[Glen Peters]

I've been lurking for a while now. Read all of the posts and have been very impressed with the knowledge and responses to questions. Excellent forum.

Now for my question. I have a LaserPro Mercury 25 watt laser. When I print (send something to the laser for engraving) there are several setting that must be input, i.e power, speed, miror, invert, mode (black& white,manual color fill, 3-D or stamp) and DPI and PPI. By default my DPI and PPI settings are 500 and Auto respectively. I can leave the PPI set on Auto or manually set it to 30 or 50 to 1500 PPI in 50 PPI increments and the DPI to 200,250.300,500,600 and 1000. Does anyone know what the actual PPI will be for a given DPI setting when set to Auto. My machine's manual is totally useless. The manufacturers site didn't shed any light on the subject to me. Have Googled quite a bit on the subject but found nothing specific. Tech support, DUH?

Logic tells me that a 300 DPI graphic should be lasered at 300 DPI and 300 PPI otherwise the machine would be required to do a lot of interpolation. I have tried different combinations of DPI and PPI settings with mixed results.

Is there a rule of thumb for these settings? Any comments or links on this subject will be greatly appreciated.

Thanks

Glen

[Kevin Dill]

Hello Glen,
The manual I recieved with my M-Series is slightly older than the one that is posted on their website. Here is an excert from there explaining what DPI and PPI is.

DPI is the number of passes the laser makes per square inch. The settings affect the raster part of the image. If you are using 50% of the power and 100% of the speed with 500 DPI and change it to 1000 DPI. It is like putting 100% power and 100% speed in that same one inch.

PPI stands for pulses per inch, this pertians to vector cutting. By changing the amount of times the laser fires per inch, the distribution of energy is changed. The range is from 30 to 1500 PPI or you can choose auto mode. When choosing auto mode, the system will assign the proper PPI value corresponding with the DPI. When using something like wood, you do not want your PPI set to high. Anything about 300 will make the edges to burnt. When using acrylic, if you don't have it above 1200 your edges will not come out smooth.

Let me know if that helps.
Kevin

[Glen Peters]

Thanks for the information, it helps much. I'll keep reaserching and studying until the "big light" comes on and I am comfortable with it all. Meanwhile I'll keep doing as I have been which has given me satisfactory results.

Sometimes a little slow on the uptake,
Glen

[Ken Garlock]

Glen, I don't know anything about Laser WW, but your question got me curious so I checked over at Whatis.com (http://whatis.techtarget.com/definition/0,,sid9_gci214320,00.html) PPI in the computer world means Pixels per inch. Of course their definitions are for Computer monitors, but it sounds like it should translate to your work :)

Take a look, it will either explain or make things worse :(