What a topic near and dear to so many artists and printers in the digital age: DPI VS PPI.
Admittedly, I am one of those artists myself and throughout my career, I have encountered clients with this question on more projects than I could dare remember. So just what exactly is the difference? What does each term mean? Why does it matter? How will knowing about DPI vs PPI help me? Those will be the topics of this article, and hopefully I will help clear up some confusion.
Let's start with something simple to get the ball rolling. Both terms are references to formatting specs in relation to image quality, but they refer to two distinctly different sets of media.
For example, most Imaging softwares will allow the user to manually adjust their specs according to preference, but if I go into Photoshop and wish to adjust my image either before beginning a project or before saving it, I am given the common options to specify my image quality by either PPI or PPC, but not DPI or DPC. There are exceptions, however.
This is because the software I've chosen is explicitly geared towards a digital format first, only concerning itself with physical descriptors at the point in which the material is to be translated between mediums. However, if I were to be using a large scale/wide format printer, then prior to print, either the printer software itself or the print settings in my digital imaging software, may allow me to adjust by "DPI" or "DPC."
If as a content creator I were uninformed to the difference between these terms, it could cause drastically reduced quality, or exaggerated sizes when I send the image to print. Hence the need to know "DPI vs PPI."
DPI vs PPI
What is DPI?
Let's start with the older format. DPI is a term that applies to images of both digital and physical variety purely because it is the means by which the printer software has to communicate the image structure into a physical production. Printers were dealing with DPI back in the days of hard set printing, even before PPI was even a glimmer in some inventors eye.
"D" stands for "DOT," and "PI" as traditionally represented across both terms, translates to "Per Inch." Many programs will often offer PC as well, which means Per Centimeter. Sounds fairly simple right? Dots Per Inch. But wait, what's a dot so far as technical terminology? What exactly classifies as a dot? how big is a dot? What is the composition of a dot? Can a pixel be considered a dot?
Well, allow me to explain. To a modern printer, every pixel is put together by different colored inks. Traditionally, as many of you may know, these have been C-CYAN, Y- YELLOW, M-MAGENTA, and K-BLACK. There are a lot of printers which use larger variances these days, but for this description, we will stick to the old CYMK.
Now, due to the limited number of colors that a printer works with, it has to mix those inks just the right way to make everything else, and if you have a single pixel that is not one of those colors, then it has to replicate that color through a careful combination. So the printer needs to process the information by using something smaller than the pixel. The pixel has to be translated. This is where we get "DOTS." Each pixel replicated in the printing process, is created by a series of smaller, corresponding dots. This is also why dots predate pixels and were the original standard.
As a result, the greater your DPI, the smoother the transition between colors should appear. It will print slower and it will require more ink because your printer has more work to do, but it will look smoother in close up view. Of course, not everything is meant for a close-up view and sometimes what you're printing is a 40 ft long banner that will be 20 feet up on a wall. So in those cases, you can lower the DPI settings until it looks good from 20 feet away, and then your printer won't waste all the ink and time it might otherwise.
To summarize, in regards to DPI vs PPI, the DPI is the number of dots of ink in every square inch of substrate to make whatever colors are presented in that inch.
Maybe you don't plan on printing though, or that's "not part of" your job. You may feel that's something for the printers to worry about, but don't count on it. You just need it to look good on screen. Well then, that's where the next term comes in.
What is PPI?
Well, if DPI stands for dots per square inch, then "PPI stands for... something else per square inch?'" you might say. If you do say that, then you're either very new to this, or you're very much removed from the digital side of the business.
The P stands for PIXELS, and since I explained what a dot was, you can pretty well know that I am about to explain pixels as well.
Pixel, as a word, literally stands for "picture element." They are the smallest physical piece of a digital display device that the eye can see. They are basically the little atoms of the digital spectrum. They're way bigger than atoms, and are made up of light emitting components, but it's still a good way of looking at them. There may be something smaller out there, but you can't see it, and as a visual artist, that's all that matters.
Pixels are those itty-bitty little squares and such that make up your image. The more of them you have, the bigger your files get, (which can be frustrating if your memory space is limited) but the less of them you have, the more the jagged and "pixilated" the picture looks.
The funny bit is that even though you can work in PPI well into the hundreds, most traditional screens were only designed to view at roughly 72 PPI. This has changed over the years and now we have many higher screen resolutions, but you can't adjust the PPI of your screen. Your screens PPI is "fixed." It's set.
You cannot type in a new setting and adjust a 130 PPI monitor into a 300 PPI. You can only adjust the PPI settings of the image you're working with as a way that your computer can tell you the difference upon zooming in or out to adjust for an approximation of what that image might resemble in print at that size.
If you never plan on printing the image, then you could honestly set all of your work to 72 PPI and just adjust the overall dimensions to the viewing size of whatever screen you want it seen on. Sure, It won't look great on zoom and It's large-scale print quality won't be glorious, but the easy solution to that, is simply not to zoom in or to print the image.
The problem with that is that most of us do plan on printing or having our work printed at some point. This is why I actively suggest that any artist, specifically avoid saving their work in 72 PPI unless it is meant exclusively for net or application use.
Ok, so since pixels are an element of a screen and dots are an element of a printer, then pixels, as translated into more tangible mediums, have no fixed size outside the screen. The printer doesn't know how big a "pixel" is. To a printer, pixels are just an idea. Consequently, if you increase the size of your image, then the printers idea of those pixels, just scales up accordingly until that tiny little square edge that looked half the width of a hair on 10 percent zoom, suddenly becomes a glaringly jagged edge at 100 percent print.
That can be a problem admittedly, but guess what news I have for you; it's not your printers job or your print shops job, to redraw your work at higher resolution just so you can see a smooth result. They'll not only charge you more but often enough, they'll dislike working with you because you don't send your images in work ready quality.
So how do you increase or decrease print quality using PPI settings? By manually adjusting those PPI or PPC numbers, in program, to reflect your intentions before you work, or before you save said work. I highly suggest looking up the details for this in accordance to your intended size. Everyone seems to have their preferences, and some will insist on higher PPI than is necessary, but in the end it is up to you to know the specs that will satisfy your project.
Hopefully, this just made a lot of digital artists respect their printers a little more and vice versa. Meanwhile all the vector artists out there are laughing at us.
What's the Difference?
In the great DPI vs PPI discussion what needs to be taken away is this:
So what is the difference between DPI vs PPI, really? Does it matter? Unfortunately, a great many people seem to use these terms interchangeably. I know that I've worked behind the printer and behind the screen and I've even done it before. Honestly, I still do it with clients all the time just to avoid making them confused.
Not many people will say PPI in the course of an average day. Sales people trying to pitch TV's, digital cameras and monitors mistakenly say DPI all the time, and no one bats an eye at the mistake. They are wrong, but do we really care about DPI vs PPI? I can definitely tell you that printers do, and if any of these things mentioned are a part of your job, then you should too.