Sizing Up Your Images & Understanding Resolution - Part 2

So this article is about dispelling the myth that an image’s resolution for screen display should be set to 72 ppi. A lot of people will cry foul and others will applaud that yet another somewhat false narrative has been exposed …

Let me explain a few things about image resolution; image resolution only matters when you press Print or your intention is to have that image printed at a photo lab. By default, the accepted universal resolution for printing is 300 ppi. This means that you are packing 300 pixels per linear inch and the accepted practice is that we require this much information in order to get a great quality image back from the lab or your ink jet printer.

I believe that most of this has been covered in detail in Part I of this article but I do want to mention that not all ink jet printers (companies / brands) put ink dots on paper the same. For example, Canon and HP ink jet printers work best at 300 ppi but some Epson ink jet printers work better at say 360 ppi. This is not a knock against Canon or HP, its just that Epson printers use a different technology which allows for finer dots of ink to be placed on the paper.

One more thing about printing; the previously mentioned image resolutions for printing is not required for poster sized prints. What’s poster size you ask? Let’s say anything larger than 13 x 19 inches. It all has to do with viewing distance. Images printed up to say 13 x 19 inches will be viewed at a relatively close distance but anything larger is typically viewed at a distance of at least 3 feet and possibly 6 feet away.

For example, any sized print up to about an 8 x 10 inch, you would hold in your hands at arm’s length. Anything larger say up to 13 x 19 inch print, you would have to extend those arms to their max in order to take in the entire photograph. We’ve all done it at one point or another. If you were to hold a 16 x 20 inch print at arm’s length you probably would not be able to take in the entire photograph but rather scan portions of it and to view it properly you would have to lean it up against a wall and step back a bit. Does this make sense? I hope so. So now if you are viewing a 16 x 20 print at a distance of say 6 feet, you don’t necessarily need that print to be printed out at 300 ppi (or 360 ppi) - You probably could get away with a print resolution of 240 ppi - you see, your brain and eyes have the ability to fill-in the blanks so to speak so that image looks just as amazing at a 6 foot distance as it did as an 8 x 10 inch print hand held. Also at those larger print sizes, if set to 300 ppi, would occupy more space o your hard drive and would take longer to print, and to be honest, most people would not and do not notice any difference in the quality.

Let’s go to an extreme example and then you can tone it down to whatever makes sense to you. Those billboards you see while travelling along the highway that are far off in the distance. What resolution do you think those are printed at. One printer (the person and not the machine), that I was talking to way back said that they printed those billboard images at 9 ppi. That’s not a very high resolution but at that distance and at the speed the vehicle is travelling, our eye and brains fill-in the pieces so those image look as good as they do.

So when it comes to resolution for displaying images on a screen, the only thing that matters is pixel width and pixel height or one or the other depending if the image is taller than it is wide or wider than it is tall. This is why when asking about images sizes used for social media platforms, all the information is in pixels and not inches. Screen devices display in pixels. You do know where the word ‘pixel” comes from right? Picture Element.

So the best thing to do is figure out the resolution of the output device and obviously the physical size of said device. You can find out all the required pixel dimensions online.

So here’s the rub; if only pixel width and pixel height matter for screen display, then why does image resolution even matter? It doesn’t! And I’ll show you below. I’ll use the same image as I did in Part I of this article.

Before I do that I want to just explain to you why 72 ppi became the norm in the first place. Back in the beginning of desktop computer imaging, Apple was the graphics platform and the other platform was for business purposes. Besides all of the professional graphics applications were Mac based in the beginning. Yes, eventually the professional graphics applications were ported over to the other platform(s) and business applications were ported over to the Mac platform, but I digress.

When Apple started out creating desktop publishing applications with the intent of replacing the person working in the graphic departments, Apple wanted to make that transition as smooth as possible. In order to achieve that, Apple had to make things as simple as possible. Don’t forget that most working in the graphic arts industry were, not all, but a lot were middle-aged and were content doing what they have been doing for a very long time and change was not a thing welcomed easily. I know because I had been working as a photographer for a newspaper chain in those days and knew people in both the graphics and production departments well. To go from physical pen & paper and ruler to a computer screen was very intimidating to say the least. So Apple decided to make things as easy as possible by creating a one-one relationship incorporating some old school knowledge with new school equipment. They made things out to be 1:1.

In the world of Typesetting things were measured a few different ways; points & picas were most common. On point equals 1/72 of an inch, so 72 points would logically equal 1 inch. Since this was common knowledge for graphic artists and since Apple wanted to make the transition easy, Apple decided to make their screen resolution 72 pixels per inch. So when an old school graphic artist was transitioning to digital (for some, a very painful process), they could hold up for example, a headline from a newspaper that was printed at a one inch height to the computer monitor to a similar headline using a font size of 72 points, things matched up.

So now you know why 72 ppi - or as Paul Harvey would say at the end of a broadcast “Now you know …. The rest of the story”.

Meanwhile the PC world had a screen resolution of 96 ppi. Nothing wrong with that as it was a function of the video cards - at least that is what I was told decades ago. Over the years, screen resolution has increased but the use of images set to 72 ppi for screen display has remained the same. I can only assume that image based applications such as Adobe keep using 72 ppi because it is easier to maintain what was, as opposed to what is.

In the following series of images or screen captures, you’ll see that I change the image resolution from 300 ppi to 72 ppi to 999 ppi and then to 1 ppi and it makes absolutely no difference to what you see on screen.

Notice that the above image is viewed at 100% and the resolution is set to 300 ppi.

Image Size (disk space occupied) is 2.2 MB

Dimensionsare 999 px x 799 px

Notice that the above image is viewed at 100% and the resolution is set to 72 ppi.

Image Size (disk space occupied) is 2.2 MB

Dimensionsare 999 px x 799 px

Notice that the above image is viewed at 100% and the resolution is set to 999 ppi.?

Image Size (disk space occupied) is 2.2 MB

Dimensionsare 999 px x 799 px

Notice that the above image is viewed at 100% and the resolution is set to 1 ppi.

Image Size (disk space occupied) is 2.2 MB

Dimensionsare 999 px x 799 px

Notice that regardless the resolution chosen, the on screen size that the images is displayed at does not change.

So, going back to my original statement that an image’s resolution only matters when it comes to pressing “Print” is in fact true. Prove me wrong …. I’ll wait.