Minimum Printer Resolution?

[kienjakenobi@gmail.com]

In the article "Understanding Resolution," an example of an Epson printer with a 1440 dpi is used.  To show the minimum acceptable ppi of an image printed on this printer, 1440 is divided by 6.  The only connection I can make with this six is when it is said that this printer uses six colors to print color images. Is this saying that the minimum acceptable ppi of an image I send to my printer should be the printer's dpi divided by the number of inks it has? (Let us stay on Ink jet printers)

Thank you

[Eric Myrvaagnes]

Yes, I think that is what Michael is saying. That is because each dot of color on a print is obtained by some mixture of "dithered" dots of each of the colors of the printer. This makes some sense for printers like the Epson 12xx series which had six colors.

It is interesting to note that when Epson introduced its "Ultrachrome" printers (the 2100/2200 and up), they went from six to seven inks, but still used 1440 and 2880 dpi as standard print resolutions, even though neither of them is divisible by seven.

This raises another question: Do the new 12-ink printers from various makers require printing at 28880 dpi to get the same apparent resolution as an Epson 1280 (6-ink) printer at 1440 dpi?

Eric

[kienjakenobi@gmail.com]

Thank you Eric.  That is an intriguing question.  It seems to me that is would only mean that a print of equal quality on the 12 ink printer would require a smaller ppi out of the input image.  I do not see how it makes sense that having double the number of inks causes minimum acceptable ppi to halve, but using this formula it does.  1440/6 = 240, while 1440/12 = 120.  I do not see how having more possible ink combinations decreases the needed ppi, but unless this formula allows for quality degradation the more advanced the printer is, that is what the formula says.  

Also, my printer says it has 2400x1200 dpi.  What does that mean?  I have seen printer dpi written in this manner before, but it does not make sense in comparison to the more often stated "1440 dpi Epson printer."  What is the second value for?  

Thanks

[nemophoto]

The DPI settings and requirements have nothing to do with the numbers of inks. You can have 4, 6, 7, 8, 12 or whatever, but this does not change the printer's resolution, which is only the total numbers of dots the printers can lay down in a square inch. Epson uses 1440/6 as a basis for printing at 1440 DPI. Similarly, if you print at 720, use 360 or 180. All these numbers mean that the printer's driver does not have to go through odd numbers of interpolations to achieve the desired print quality. While 300DPI is ideal for offset printing, it is not necessarily optimum for inket printing.

[michael]

Nemo,

Quite right. The number of inks have nothing to do with it.

Michael