PPI vs. DPI: What the Heck Is the Difference Anyway?
In the world of printing, the abbreviations “ppi vs. dpi” get thrown about quite a bit. What does it mean?
Do you have to know the difference to get a good quality print?
Or is it just something the tech nerds like to use to impress themselves and each other? Sort of like all that talk about moiré patterns you might have heard about; this is all about tiny, seemingly insignificant dots or squares. Should you care?
Well, if you want to produce top-quality prints, then it’s beneficial to know what ppi vs. dpi means. Understanding the mysteries of these letters means you’ll know how to save graphics in the best way.
If you aren’t doing the printing yourself, then your printer will be a happy camper. The artwork will look sharp and high resolution because you did some homework. Sometimes, it pays to be a bit of a tech nerd after all.
Resolution: What to Know About PPI vs. DPI
It’s all about resolution, but they aren’t the same thing. Information about the difference between ppi vs. dpi is often confusing. In truth, sometimes it seems like the experts do their best to keep it that way.
We’ll do our best to present it in such a way that you’ll understand the difference without getting too pixelated about it.
Dots per inch
DPI stands for “dots per inch.” The dots in question represent tiny dots of ink that printers use to create an image on a substrate. The dots per inch is a measure of the density of dots on the page. Different printers have different sized dots. There’s no set size or shape, which means the way a picture looks on each machine can vary quite a bit, depending on the manufacturer. There’s a physical limit to how many dots a printer can render.
When it comes to printing the dots of ink, printers often use CMYK inks. This stand for Cyan, Magenta, Yellow, and Black. Various specific mixtures of the four colors output as tiny dots can produce thousands of shades and hues in a final print.
The color white shows through from the paper background when no CMYK is used. Very generally speaking, an inkjet printer needs to put out 300 dots per inch to create a quality (or at least decent-looking) print. Are you starting to see the difference in ppi vs. dpi now?
Ink dots aren’t pixels
Now, if you want to create a file that prints at 300 dpi, then you’ll need to be aware that even in popular graphics programs like Photoshop, ppi vs. dpi is often used interchangeably. To create a 300 dpi image, you must change the image resolution using the field for ppi, pixels per inch, not dots per inch. It makes you think they are the same thing, but again, they are not.
Once again, ppi vs. dpi is super confusing, right? In actuality, the printer can still alter the dpi by choosing a particular printer or selecting printer output settings. You have zero control over the actual dpi, the dots, that a printer spits out.
See the video below to see what we mean:
Pixels per inch
The pixels per inch is a measure of pixel density on the screen, not on a printer. Printers do not print in little square pixels; they print in droplets of ink. There can be a limitless number of pixels of various sizes in an inch of your screen.
The manufacturer’s screen design determines the limits. Today, screens with higher pixel resolution are becoming extremely popular, such as 4K, HD, QHD, and UHD. To calculate the exact number of pixels in an inch for these screens requires a relatively complicated mathematical formula.
If you cram more pixels into an inch, you tend to sharpen the resolution. In general, a very high definition screen may have something like 109 dpi, but most monitors have a resolution of something like 72 dpi.
That’s why, as a designer, you create graphics for digital mediums on screens in an entirely different way than you would for a print. Generally, digital files will end up being a much lower file size than files with the high resolution needed for printing.
See a good description of ppi below:
Screens vs. Printers
Are you creating images that will be seen exclusively online, on computer monitors? Or are you preparing files to be sent to a printer for use on paper or vinyl or some other substrate?
Unless you are working with a high definition screen, the general rule of thumb is this:
- 72 ppi for monitors
- 300+ dpi for printers
Let’s take a more in-depth look at this.
The Best Resolution for Printing
Suggesting there is a “best resolution” for printing will make many printers and graphic designers cringe. They know there are a wide variety of variables, including how big the image will be and how far away viewers will be when they see the print, such as a billboard.
For a billboard, a resolution as low as 20 to 50 dpi will work, since viewers stand so far away. From a distance, the viewer doesn’t notice the larger dots. For a notecard, that same resolution would look like a highly-dotted halftone pattern.
Further complicating the answer will be what type of paper is used.
Is it newspaper or high-quality glossy paper? Is the paper coated or uncoated?
Then you must consider the purpose of the print. Will it be a fine art print or an advertisement for a business?
Is high quality called for, or will it be overkill and a waste of money and ink if people won’t be close enough to notice anyway?
Suffice to say there are a million variables that your printer must be aware of, but we’re attempting to simplify the matter for this article. Generally, a printer needs more dots per inch to output a quality print than a screen requires to display a quality image.
Generally speaking, 300 dpi is the professional print standard for use in magazines or other publications.
Much higher resolutions are possible with laser or other printers for high-quality artwork. Keep in mind that the resolution will ultimately depend on what your printer is capable of printing. Thus, it would be a waste of time to try to print an image set to 800 ppi on a printer that only prints 600 dpi maximum.
Using DPI and PPI Interchangeably
If you’ve gotten this far and you’re still a little confused, then it won’t surprise you that even the tech giants have been confused about ppi vs. dpi for a very long time. In the 1990s, advertisements from Apple and Adobe used the terms interchangeably, pixelating the waters.
They’ve since corrected the issue. However, many other resources have reportedly continued to use dpi and ppi without noting the differences, including the Android developer’s guide. The motive may be to simplify the issue for the general public, but it’s helped with creating more confusion for some.
Changing the DPI
How would you go about changing the dpi of a print? The simple answer is: You can’t. Not without changing the printer that you use. Remember, the dpi is determined by the physical nature of the device used for printing. OK, here’s one way: You could whack the printer head with a hammer and thus create one enormous dot covering the entire page. We wouldn’t recommend it.
The more nuanced answer must take into consideration that imaging programs and many people often use ppi and dpi interchangeably. So, changing the “dpi” may not be what you’re doing when you change the image resolution in Photoshop, but for all intents and purposes, that’s how you’re going to create a high-resolution file to send to the printer. Roll your eyes if it helps, but that’s the gist of it. We feel your pain.
Changing the PPI
This time, you can change the ppi as much or as little as you like. Similar to the limitations of printers, there are limitations of screens, created by the manufacturers. But generally, the longtime rule is that images only need about 72 ppi to look decent on a computer screen.
It’s critical to keep in mind that most newer computer and television screens have a significantly higher resolution than 72 ppi.
However, changing the ppi resolution won’t change the overall size of the image on a screen, and it may not change how it looks on screen very much. For that reason, some suggest it’s a waste of time to convert images to 72 ppi for use in digital media.
The main reason why you might want to do so is that pictures with low resolution tend to be smaller file sizes, taking up less memory and storage space.
On the other hand, changing the ppi will change the size of the image when it goes to print. If you change the size of the image without resampling it, the print size will get smaller as the image resolution goes up. This fact can be a very confusing problem for some people who want the image size to stay the same but want a higher print quality.
The other problem is that your final image quality will depend on the quality of the image you started with. Increasing resolution of a bitmap image that began as low resolution will almost always result in a blurry, low-quality image when it goes to print. Oh, and the customer may not understand why. Joy!
Although you may never need to know this, modern LCD screens use sub-pixels, one for red, green, and blue, of the RGB additive color model used on screens. Adding all the light colors together makes white. In comparison, the CMYK color model used for printing is a subtractive color model. Combining all the color inks together makes black.
A mixture of the three sub-pixels represents one pixel on the screen. It’s useful to know about sub-pixels because they can be manipulated to create sharper images on the screen.
One way is through anti-aliasing fonts so that they appear sharper without blurry edges. Smooth lines become important on the screens of smartphones, for reading crisp lines of text and tiny icons.
It’s an interesting thing to know, although it may only be useful to you if you get a question about it from a professional graphic designer or printer. We’re giving you the finest of details on ppi vs. dpi.
When using an image editor like Photoshop, if you change the image size without clicking the all-important checkbox marked “Resample,” then you don’t change the number of pixels at all. If you check the box, then the pixel density, or resolution, will change, along with your changes to the overall length and width. Photoshop will physically change the number of pixels in the image.
The program uses interpolation algorithms to decide which pixels to eliminate if you reduce the image size or how to add pixels if you go larger. Very often, the program can do a great job of resampling and increasing print quality, but it can only do so much.
The best path to an image that prints out sharp is to start with a high-resolution image. We’ll look at how you can achieve that with bitmap images next.
The best quality prints start with high-quality artwork, digital images, or photographs on film. Photographs on film are not made up of the dots used for printing, and you can scan them at the highest resolution to get a very dense ppi image.
If you scan a newspaper, magazine, or other printed picture, you will pick up the ink dots and halftone patterns used in the printing process.
Scanners will allow you to scan at high-resolution ppi, depending on the manufacturer and model. If you are starting with a small image, it will generally pay off to scan it at high resolution; then if you need to blow up the image size, there will be enough pixels there to work with.
It’s no guarantee your image will look great at a larger scale, but it’s better than starting without enough pixels.
Yes, many scanners and instructions for how to use them will ignore the difference between ppi vs. dpi. You’ll have to take what they say with a pixel-sized grain of salt.
Get the Picture?
We hope that you now have a much better understanding of ppi vs. dpi. You’ll no doubt come across dpi masquerading as ppi, whether it be at your local copy shop or even from well-educated graphic designers and printers. Long ago, it seems the two terms melded together irreversibly. However, now you get the real picture.