pixel pixels ppi dpi

Welcome to part one of the 10,000 part series, “How to properly over-explain a simple concept.” The goal here is to answer some simple questions that most people will have thought about at one time or another. Today we’re exploring the wonderful realm of pixels* and how images are displayed digitally, as opposed to how they’re traditionally produced in print. So grab on to your monocles, ‘cause here we go.

Dots Per Inch
If you’re somewhat familiar with print design, you’ll know that printing is measured by DPI, or dots per inch. Simply put, when an image is printed on a substrate (e.g. paper, vinyl, etc.) the clarity that the image can achieve is determined by the amount of dots of ink a printer can squeeze into a square inch of substrate; it can also be affected by using a very low quality image, but if you’re doing that then your production workflow is bad and you should feel bad*. However, not everything is printed as clearly as it can possibly be printed. A magazine might be printed at 300 dpi, but an image on newsprint might be printed at 150 dpi. Outdoor boards will drop even lower, usually falling in the range of 15 to 30 dpi. But why are they different, and why does this concern you, the guy that googled ppi and not dpi?

Print resolutions vary for a few different reasons, but there are two big ones. The first is cost. If you’re using a low DPI then you are by extension using less ink, and thus saving money. Newspapers* are printed so often and discarded so readily that using less ink on lower quality paper saves tremendous costs over time. The second is viewing distance. The further you are from an object, the less likely you are going to be able to notice any of its finer details. This is why outdoor boards can be printed at such low resolutions. Since you’re viewing it from hundreds of meters* away, the image will still be perceived to be clear despite the fact that it is pretty blurry up close. You can save money by printing at a much lower resolution while at the same time not affecting your consumers’ perception of the image.

Pixels Per Inch
Ok, enough about print production. How is this related to digital images and digital displays? Much like print design, the clarity of an image that’s represented digitally can also vary depending on how it will be presented to the consumer. And just like anything else humanity has magically concocted, the technology to do so has improved tremendously over time.

Traditionally, digital media is created at a standard resolution of 72 pixels per inch. The story for how this number came about is rather long and boring. Suffice it to say some nerds in the fuchsia-colored, aerosol propped, godforsaken era known as the ‘80s* decided it was the most efficient resolution to relate images on screen to how they would appear on paper. Today, digital media continues to be produced at this standard resolution. But 72 ppi isn’t necessarily what you are looking at when you look up puppy photos on Instagram. Not anymore, at least.

Digital Displays: How Many Pixels Are There?
If images and video are created at 72 ppi, does that not mean that I’m looking at 72 pixels if I press my face against my iMac? No, not really (although I suppose you could be pressing pretty hard). Much like how cost affects the dots of ink used to print an image, the quality of the display will affect how many pixels are being used to present to you the image you are viewing. Similarly, the quality of the display that is required for any given task will also vary with the expected viewing distance of the consumer.

Let’s look at a few screens familiar to everyone: smart phones, televisions and scoreboards at athletic events. Manufacturers know that a smart phone will be used at a very close distance, sometimes even centimeters* away from discerning eyeballs. They also know that no one wants to be carrying a brick in their pocket. For this reason smart phones are pound for pound the pixel champions of the Earth. Pixels are crammed so tightly into such limited space that the resolution of those screens will be closer to 300 ppi (or more!). Not only that but resolution varies from say, Apple iPhone to Samsung Galaxy, as well as from generation to generation as technology continues to improve. The proximity and frequency at which they are used means that despite costing more (looking at you Apple), a higher quality display is often preferable.

Televisions have also improved over the years. Going from those enormous CRTs to the beautifully svelte HD TVs we have now was a tremendous leap. Cost, however, is a somewhat more significant deterrent to a widespread resolution revolution in TV. Remember being yelled at for sitting too close to the TV? Turns out that sticks with most people. Viewing distance for TV is expected to be around the 1 to 3 meter range. TVs do have a tendency to cram more pixels into their screen sizes than your standard 72 ppi, but most don’t stray too far. Unlike phones where the highest clarity possible is the standard, with TVs the quality varies more often from brands and models as consumers decide how much they want to spend for an improvement that may or may not be noticeable from their couches (although it should be noted that other factors such as frame rate affect video quality, not just pixel resolution, but that’s a discussion for another day).

Scoreboards and other types of digital outdoor displays are similar to their print counterparts. No one is likely to view them from up close, and on top of that the costs of manufacturing a screen that large with several billions of pixels approaches Waterworld* levels. The resolutions of these displays vary wildly, but it’s pretty rare for any of them to even come close to 72 ppi. What ends up happening in this type of display is that despite images being created at 72 ppi, they are stretched out so far over larger pixels that are further apart that it likely ends up being seen at 15 ppi or less.

Why Does It Look Weird?
In conclusion, if you have ever looked at an image on your phone, then looked at it on your PC, but then emailed it to your grandma for her to get your nephew to open it up on her iPad that you got her for Christmas (to the great inconvenience of your nephew), and thought, that looks a little different, now you know part of the reason. Unlike print, which has a set resolution until it fades away due to the ravages of time, digital media varies from display to display. But, if we have the ability to provide more pixels, why don’t we just create higher and higher quality media as technology improves? Well, at that point you are entering the wonderful world of bandwidth and optimization for network limitations. Display technology may have improved, but other parts of the equation continue to lag behind. That may sound like a whole lot of nonsense to you, but simply put it saves you a lot of money on your data plan and your cable bill… if you still have one of those. We’ll probably go more in depth into that subject at a later date, so stay tuned!

*References found in this here blog post:

  1. Pixels: This is a section within a digital display that produces a dot of light in order to create an image, not the much-maligned Adam Sandler “comedy” by the same name. It is my understanding that some people saw it.
  2. “Your ___ is bad and you should feel bad!” is a reference to the animated magnum opus known as Futurama, and the subsequent meme tornado that wonderful show has spawned for all to enjoy.
  3. Newspapers were a 20th century form of communication that allowed news media companies to cheaply and reliable provide information to the public on a daily basis, and gets its name from the familiar low quality paper used.
  4. Meters are a form of measurement found in the vastly superior metric system America continues to ignore at its own detriment because reasons.
  5. 1980 through 1989 is the era known as the ‘80s, a time when music and fashion could objectively be considered as a whole to be of significantly lower quality to the decades before it, and after it.
  6. Centimeters is more metric system, and yes, it’s still better.
  7. Waterworld was a late ‘90s Kevin Costner led movie production that was given a specific budget and strictly instructed not to go over it, and then proceeded to barf all over those limitations in order to create the single greatest film about a half-man half-fish ill-humored dude in a boat that could possibly be imagined, which turns out is still pretty mediocre all things considered.