First things first, let’s define our terms so we know what we’re talking about. Unfortunately, DPI is often used simultaneously to refer to two distinct topics. While both describe DPI as Dots Per Inch, we must recognize the difference between a printer dot and a pixel dot.
Because of this confusion, in this article we will be using DPI to refer to Printer Dots Per Inch, and we will be using PPI to refer to Pixels Per Inch. Thankfully, industry leaders like Adobe have also adopted this distinction.
Raster images are made up of pixels, so when we print them, we naturally are printing at some specific pixel density. And when we set up our print job, we are also selecting a resolution that reflects the number of ink droplets used to print the image. A common use example would be printing a raster image at 300 PPI (pixels per inch), using a printer dot resolution of 1440x1440.
Pixels Per Inch
You may have heard that 300 PPI is the standard for printing. This has a lot of truth to it, but it’s not a steadfast rule. And learning when its appropriate could save you from making some errors in pre-press.
Roughly speaking, 300 Pixels Per Inch is a standard where the print looks nice and detailed even when you have your nose up to the piece. This is usually the goal with fine-art prints. Printing with lower resolution will mean that your image is either pixelated or blurred, and most printmakers will want to avoid that.
Printing with a higher resolution, which is an option on most fine art printers, will produce details you may need a loupe to notice, and are generally recommended when printing from vector sources (like a text layer in a Photoshop document).
However, not every print needs to be up to those high standards. Consider a billboard, for an extreme example. Standard billboards run 14 feet high and 48 feet wide.
At 300 pixels per inch, that’s 50,400 pixels tall and 172,800 pixels wide. Certain elements like text and logos can be vector, and will scale up infinitely. But as far as photographic images go, best of luck trying to find source or stock images that are 50,000 pixels tall. For a billboard, that doesn’t matter. Lower resolution images can be blown up because nobody’s putting their nose up to one, they’re viewing them from hundreds of feet away.
The same is true, to a smaller extent, with signage and décor printing. For commercial printers, the client’s satisfaction is going to trump an insistence on never printing below 300 PPI. Sometimes a graduation or family photo will need to be blown up. Or sometimes the client needs something on a wall graphic where perfection isn’t the expectation. Here’s a general guide to know what you can get away with vs what will be obviously pixelated or blurred.
- 600 PPI – Looks okay through a loupe – text in particular
- 300 PPI – Looks okay with your nose to the print
- 180 PPI – Looks okay from about a meter away
- 100 PPI – Looks okay from about two meters away
Beyond these benchmarks, your results may vary. The best way to know what looks good in a specific location would be to make your own prints and judge for yourself. A hard proof may be a good idea so your customers understands the quality possible from a given source.
Printer Dots per Inch
The difference between a printer dot and a pixel is important. Let’s consider printing a pixel with a color of pure cyan. Since Cyan is a primary channel in just about any commercial printer, it is theoretically possible that one drop of printer ink could represent one pixel. But a green pixel would necessitate a minimum of two printer drops – one from Cyan and one from Yellow. A color like dark orange could require Cyan, Yellow, Magenta, and Black. Not to mention dilute inks, if your printer has them. And with fine art printers achieving printer droplets measured in the single digit picoliters, it’s likely more than one droplet could be needed to produce one cyan pixel as well.
Print resolutions are commonly displayed as two numbers, such as “1440x720”. In this case, that would mean that the printer is putting down 1,440 dots horizontally, and 720 dots vertically. Sometimes, like with Epson print drivers on Macintosh systems, print resolution is displayed as one number, such as “1440”, which means 1440x1440.
Higher dots per inch mean more ink is consumed. If you are setting up custom print modes in a RIP software, the higher resolution you go, the more you will need to restrict ink limits to prevent over-inking artifacts. However, if you are using a print driver, the manufacturer has already done this work for you, and you will not need to worry about over-inking.
For driver users, you will select a Media Type, and then have limited selections for various DPI resolutions. These are typically under a section labeled “Quality”. The printer manufacturers give you options that are appropriate to the type of media you are printing on. For example, a “Canvas” media type might top out at 1440x1440 DPI, while a “Glossy Photo Paper” may go as high as 5760x1440. The higher resolutions are not available on the “Canvas” media type, because that increase in detail would be lost in the texture of the canvas.
The options you are given in the driver should be approached as a trade off between print quality and speed. Breathing Color recommends using the highest DPI option available in the Media Type recommended for our products, unless speed is a larger priority for your business. And just like PPI, the best practice is always to test print and see what looks best to you and what works best for your shop.