Stupid printer (dpi) question, or maybe not so stupid.

Started Apr 24, 2013 | Discussions thread
JJ Winkel Senior Member • Posts: 1,387
Why stupid ? Can be simple enough.

As said before, two acronyms to remember :
DPI = Dots Per Inches and PPI = Pixels Per Inches.

- PPI :
Every home photo printer even the pro and larger pro models like the Epson 3880, have one or two fixed by hardware pixel pitches, usually 300 for the Canon's and 360 for the Epson's ( the Epson pro have 720 ppi also ), just examples as I do not know for every model. It is governed by the head carriage stepper motors accross and down the page.

This PPI value is the same as the picture's resolution set in your photo application and when related to the picture's actual width and height amount of pixels will give you the actual final print size, example a 6000 x 4000 pixels picture at 300 ppi will be printed 30" x 13.3".
Whatever PPI you have set in the photo application will eventually be converted to the printer's real physical value (300, 360, 720, ...) by the printer driver just before being printed. With the Epson Pro's you can choose which ppi to be used by ticking the "Finest Detail" option in the Print Quality tag, off = 360 ppi and on = 720 ppi.

- DPI :
Again as said before, this is the number of colour dots per inch and consequently per pixel (divided by the fixed ppi pitch). It merely controls the print colour quality and range of printed tones and smoothness, whereas ppi is more related to the picture details capability.
This value being much larger, 1440, 2880, 3000 and more (according to printer make, notice how they are divisible by the printer's ppi) is the one advertised as it is more flattering and more commercially attractive ....   
You choose which DPI value you want in the printer driver settings, your choice may be limited by the paper choice and the possible print quality for each one, example with Epson 3880 using Photo Glossy paper you can choose between Quality Level 4 = 1440 x 720 DPI and Quality Level 5 = 2880 x 1440 DPI.

I hope that's simple enough to get a basic understanding of what's going on thereĀ 

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