Inkjet Droplet Size (WAS: Storage of digital images)
2002-08-02 by Doug I.
Anthony, I'm no engineer, and tend to focus on the end result rather than the technology behind it. But it is my understanding that an Epson advantage vs. HP, Canon, etc. is that the Epsons CAN produce individual (i.e., non-combined) drops of variable sizes, while the competitors can't. If the more technologically gifted will excuse my layman's attempt to explain, supposedly Epson uses electrical impulses to control deformation of a crystal in varying amounts, thereby squeezing ink drops of variable sizes out the head. In the Epson pdf I have (explaining why a 2880x720 Epson is supposedly better than a 2400x1200 competitor), they claim exactly what you said about competitors' printers--that while they can technically produce more dots, these dots are fixed in size and therefore cannot be placed as accurately or closely without oversaturating the paper. This was the link on Epson's site: http://files.support.epson.com/pdf/600q__/600q__ei.pdf It doesn't work any more for me, but I do have the original 7 page pdf which I could email to interested parties off-list or for posting to the archives. (I found it in the FAQ on the C80, so it also contains a somewhat lame explanation of why individual ink tanks aren't necessarily more economical....ha ha.) Doug
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> > Date: Fri, 2 Aug 2002 00:07:05 +0200 > From: "Anthony Atkielski" <atkielski@...> > Subject: Re: Storage of digital images > > Bob writes: > >> When you refer to a 160 ppi or 200 ppi printer, >> what exactly are you referring to, and how does >> this relate to dpi resolution of the printer? > > Inkjet printers, like offset presses, use essentially opaque inks in four or > more colors, usually cyan, yellow, magenta, and black. Since these inks are > opaque, their darknesss on paper cannot be varied, nor can one color be > printed on top of another to blend the two. So, in order to create > variations in the darkness of the printing, the inks must be divided into > dots of variable size. When the dots are large and closely spaced, the > printing appears dark (from a suitable distance). When the dots are small > and widely spaced, the printing appears light. > > Inkjet printers, like the imagesetters used to create plates for offset > printing, do not know about variable sizes for dots; they always print dots > of a fixed and very small size. When dots of variable size are required (as > for printing halftone images, as described above), the tiny dots are > combined to form larger dots. The range of densities on a print (from > darkest to lightest) depends on the number of different sizes of halftone > dot that can be printed, and this in turn depends on the number of machine > dots (the actual dots printed on the paper) that can be combined to form > each halftone dot. > > Printing a single pixel on paper requires a halftone dot of each color. > > As a result of all this, a 2880-dpi inkjet printer cannot print anywhere > near 2880 pixels per inch. It prints far less, and there is an inverse > relationship between the number of intermediate tones it can print and the > resolution (because more tones requires more variability in dot size, but > that means that individual halftone dots must be made up of more machine > dots, which further reduces resolution). > > So ... if the inkjet printer manages 2880 dpi, and you want 256 levels of > black or green or whatever, you'll need 256 machine dots per halftone dot. > That means roughly a square of eight machine dots on a side, and 2880/8 = > 360, so 360 is the maximum number of pixels per inch that the printer can > manage with 2880 dpi, if 256 tone levels are desired. If you want more > tones, resolution goes down; if you want less, resolution goes up. > > Actual implementations are much more complicated, and shortcuts exist to > improve resolution a bit, but the above explanation illustrates why you > don't get anywhere near 2880 pixels per inch from a 2880-dpi printer. >