As I discovered today, having your images to be 300 pixels per inch is not always a good thing for print.
Epson printers, contrary to Canon and HP, have native resolution of 360 instead of 300, and so if you are going to print something using an Epson printer, most probably (it seems Epson changed their mind eventually, see below) you should use 360 and not 300.
On other hand, if you are going to print something using Canon printer, it is best to use 300 and not 360.
What Resolution Should You Choose?
Now that you have the ability to choose resolution, what resolution should you choose? Your gut reaction might be to leave it as high as possible; more is always better, right? Wrong. If that were the case, there’d be no reason for this article. Say you want to print your photo on a desktop inkjet printer. All inkjet printers have a native resolution. If the image you send to the printer is not in the printer’s native resolution, then the printer will resample the image to what it wants. If your printer has a native resolution of 300, and you send it an image with a resolution of 600, the printer will downsample it.
“In that case,” you might be thinking, “why should I worry about resolution if the printer takes care of it?”
While your printer can resample on its own, its resampling algorithms might not be as sophisticated as your image editor’s. In theory, it’s possible that you’ll get a better-quality resizing if you do it yourself. In practice, it’s hard to find a visible difference.
I can give you some general specs, though. Epson inkjets typically have a native resolution of 360 pixels per inch. Canon and HP printers typically have a native resolution of 300 pixels per inch.
The best way to find out if one resolution works better than another is to output test prints. Proper sharpening and resolution choice is especially critical when you enlarge images, but a little testing should answer the resolution question.
In the early days of inkjets, some used the 1/3 rule: Take the highest resolution of the printer and divide by 3. For example, an older EPSON with a 720 maximum resolution would require a 240-ppi file for optimal results (the magic resolution number”). Then, however, EPSON printhead-based printers started coming out with 1440 and then 2880 resolutions. One-third of 2880 is 960 ppi, an absurdly high and unnecessary image resolution. Some photographers and artists still swear by the 240-ppi formula for even the latest models of desktop printers, claiming (correctly) that for EPSONS, the native printhead resolution is still 720, so the 1/3 rule remains in effect. (According to Epson data, the input resolution—the resolution at which data is rasterized—is 720 “dpi” for desktops and 360 “dpi” for wide formats.) However, Epson now recommends 300 ppi at the size you intend to print as their new magic number; if you get to 220 or less, you start to see a difference in image quality, and conversely, you won’t see much improvement with bitmapped images by going over 300 ppi.
— Harald Johnson, Mastering Digital Printing, p. 37
And now I have a question. What if I need to print, with a very high quality, an image of unusual pixels-per-inch density, e.g., 567 or 987 pixels per inch? What will be the best approach in such a case? Are there special printers for this, which have "flexible" native resolution?