Printer Purchase - LPI or DPI?

McBain_v1's picture

Apologies for the total newbie question, and if it has been answered before then please direct me to the relevant thread, but I am shortly intending on buying a new laser printer (mono) and was wondering whether I should be looking for a really high DPI or LPA? Or are the two impossible to separate (i.e. you cannot have a low DPI and a high LPI)?

I am currently thinking of the HP LaserJet P2055d which has 1200×1200dpi? Is a Postscript printer I should be aiming at instead? Mostly my work involves rather long technical reports and environmental reports but I wouldn't want to short-change myself too much on quality. I haven't got a massive budget on this so this seems quite a good deal.

Any thoughts or tips would be appreciated.

Thomas Phinney's picture

LPI has a semi-arbitrary relationship to DPI. Overall DPI is your first indicator of print quality. Though there are other factors.

These days, PostScript is not a necessity, especially if you are primarily printing reports. Your HP does have PostScript emulation, which is a third-party clone of PostScript, in the event you need it. For your usage, I don't see any major advantage for having Adobe PostScript.

wreckedangles's picture

The short answer is: Don't worry about it. Pay attention to the above previous post. I would contend that LPI is more a concern for a designer using an offset printer—yet not as much as in days past; I'll explain why in the second paragraph. HP seems to be good about publishing its LPI and it can be useful to know in certain cases. But for a personal printer or proofing device, it's not as much of a concern. Especially if you are personally equipped with a large hard drive and lots of RAM pushing your file to your personal printer. The long answer is as follows: Knowing LPI used to be a detail that was much more of an issue prior to enormous storage sizes of digital media; think Iomega ZIP disk days. It's really a simple answer of what sort of file resolution you want to print and does the LPI on the printer allow for such a resolution? To add one more acronym, LPI has much more to do with PPI (pixels per inch) of the digital file you are saving. In other words what is the resolution your Photoshop (PSD, TIFF or EPS) file?

Let's forget the subject of your HP printer for a second and let's talk the foundation of the issue of LPI. There is a formula to use if you know the LPI output of the device (whether it's old school film or large format digital Epson or HP or even offset poly-plate) so the designer can plan the most optimal PPI for their files. This is particularly important if you have a huge newsletter or magazine with tons of photos. Example: lets assume an offset printer has an LPI of 150. (it's possible that it may print 2400 DPI or even more, but that is not the point right now.) The formula is as follows; 125% of the LPI of the printer device (or film/plate) is the absolute minimum to figure the resolution for PPI.

Let's try that; say you have a printer with 150 LPI. That means a minimum (Photoshop) file resolution size at 189 PPI. Yes, 189 PPI. I know that seems low but it works as the minimum size principle. It of course can be higher but that is the absolute minimum for 150 LPI and not get bitmapped jagged edges on photos or artwork. I've been doing this long enough to remember the days of 44MB SyQuest disk or Iomega Bernoulli media to know what I'm talking about and how to optimize file sizes.

Ever wonder where the 300 PPI file standard came from? Back then, (1992ish) when we had to figure out digital file sizes, we didn't like doing the math. Instead, we would double the percentage of a typical high resolution file that was being printed on a 6-fountain offset printer, (150 LPI to 300 PPI) and that would cover our bases. One more example: In the days before digital offset, some films were even output at 133 LPI (or lower) when they were printed on uncoated paper. The file resolution for 133 LPI was 167 PPI.

Now, back to your HP printer LPI concern. If you know the LPI, you know what the minimum file PPI size needed to print great looking artwork on the printer. The two most important advantages of knowing the minimum optimum resolution is: 1. getting the most out of your storage media or 2. when the file is being rendered for print. For instance, a file with two hundred good-sized TIFF images at 188 PPI is a much smaller file than the same two hundred TIFF images at 300 PPI! Both will print identical looking files. It not only saves storage media but when you RIP the file to the printer, it also takes much less time to print no mater how fast your computer is. LPI, DPI, PPI, whew, that's way too much info for one post but there you have it.

Tom Elder
Boise State University Graphic Design Professor

bojev's picture

I have a HP LaserJet P2055d and love it - produces clear type and has no problem with InDesign, Acrobat and other publishing files - it plays well with others.

McBain_v1's picture

Thank you everyone, especially to wreckedangles for a highly informative answer / mini-lecture, very much appreciated. I note that someone else has also posted a thread about what printer purchase to make so I will read that, armed with my new knowledge of DPI, PPI and LPI!

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