Advertisement


How can a print have a resolution of 9600 x 2400 dpi?


Question

While reading about the CANON PIXMA MG5150 printer (http://www.canon.de/printers/inkjet/pixma/pixma_mg5150/), there was a stated print resolution of 9600 x 2400 dpi. How is this value meant here, since I always thought even professional printers only print 300 dpi.

Of course they could just mean resolution without dpi, which would make sense, but why do they then write about dpi?

Thank you, Gabriel/Gabkano

2015/05/22
1
5
5/22/2015 3:51:00 PM

Accepted Answer

Printed medium works differently form screens. Screens have 3 color elements very close to each other. Each element is capable of different color intensities. Printers on the other hand produce dots of limited number of colors usually 4 colors, but can be more and have 3-4 mid tones or so. To show mid tones it has to spread the dots around. The end result is that the accuracy of each dot is quite irrelevant for the picture as many dots produce what one pixel produces on a screen.

Screens and other continuous media measure PPI (Pixels Per Inch) while printers measure DPI (Dots Per Inch), although PPI is quite commonly mislabeled DPI. These 2 metrics measure completely different things. So when somebody says the printer prints at 600 dpi you prepare a image at 150+ PPI if they say its 1200 you prepare at 300 and then stay at that because tit becomes unwieldy to go over that, unless you have pixels to spare. If you have a insanely good printer you might go up to 600 PPI.

Dot pattern

Image 1: Dot pattern of a inkjet, image by Jeff Thompson

compare

Image 2: Compare that to a screen and you can see its much much denser

Since the printer needs space for the blending in fact the image is needs about 16 by 16 dot area to represent a color range of 256 levels. In practice the rasters can be interleaved a bit so the number might be 8 or 10. Maybe less with intermediate tones in the cartridges.

So:

2400DPI /8 = 600  PPI
2400DPI /9 = 267 PPI
2400DPI /10 = 240  PPI

Off course here the printer has higher Dpi in the print head axis direction... Most likely the printer works best with something like 300, 450, 600 PPI. Depends a bit of factors that the DPI cant say. Id guess its meant to be a 600 PPI one. So while the numbers sound insanely high you dont use that kinds of resolutions to send to the printer. They have over resolution to compensate for a technical weakness (Its easier to add dots than to mix colors).

estimate

Image 3: Estimate of the actual pixel image the inkjet dot pattern represents, zoomed to match size.

It isn't obviously this simple but something like this.

TL;DR

Essentially they measure so different things that you can not compare print resolution and screen resolution without considering what the image is.

2015/05/20
6
5/20/2015 11:13:00 PM

OK, I left so many comments in here that I thought I better provide my own answer.

The "300dpi" rule-of-thumb comes from the world of offset printing.

4 color offset printing uses something called a line screen to create a halftone pattern of evenly spaced, but different sized dots.

Offset printing can typically print up to 2400 dpi or even much higher. However, that would be only when you're using 100% of a color--so there'd be no dots. So for text and flat line art, you would want to send an image at that resolution. This is usually handled by simply being a vector image.

For photos, however, because they are continuous tone, to print all the color variations of a photo, they have to turn it into a halftone, and the process of turning it into a halftone means it only needs a certain amount of data, that being typically 300ppi. You can certainly send a 600ppi image to the printer, but you likely won't notice any difference when printed due to the conversion to a halftone.

Example of a halftone image:

enter image description here

Now, all of the above refers to commercial offset printing. Inkjet printing is quite a bit different. Most ink jet printers use stochastic printing. Instead of a halftone of evenly spaced but different sized dots, stochastic printing uses all the same sized dot (very small) and varies how many it puts down in each area.

Because of that, high-end ink-jets can print photos much better than most offset printing can. And, because of that, you can often send much higher resolution photos to the printer and see a difference.

As for why this printer has a different resolution in each direction, that's due to the mechanics of the printer. Many ink jet printers can print in a higher density in one direction than the other.

Example of a stochastic image:

enter image description here

(Both sample photos are taken from this pretty good overview of how ink jet printing works: http://www.thetonesystem.com/inkjet_basics.html )

2015/05/21