PPI vs DPI: What’s the Difference and Why It Matters to Photographers
What is the difference between PPI and DPI? Both are related to the resolution of an image or photograph, but they are completely different measurements.
Have you ever seen a print in a gallery, or a high-resolution display, (retina, 4K, 8K, etc) …and felt like you were actually looking through a window to the real thing, because of how finely detailed the image was? That is thanks, in part, to extremely high resolution. PPI and/or DPI played a critical role in that viewing experience!
Oppositely, an image can appear blurry if its resolution is low. This is why it’s crucial for anyone involved in photography, graphic arts, and virtually all forms of visual imagery to have an understanding of how to balance various constraints (such as, the cost of a high-megapixel camera, or a better printer) with the need to make images look their best.
The Difference Between PPI and DPI
Here’s the quick and simple answer to this question: “P” stands for Pixels, “D” stands for Dots. So, it’s Pixels Per Inch and Dots Per Inch. Pixels are electronic “dots” of light on a digital display screen, and Dots are individual dots of ink in a printed image. Either way, PPI and DPI are per-inch measurements that help you understand the resolution of your whole image. The more pixels or dots per inch, the more finely detailed an image can appear.
What Is PPI?
PPI stands for Pixels Per Inch. That is, how many little electronic pixels of light can a digital display fit into one inch? At a minimum, many (older) displays used to have 72 PPI, however, now with higher and higher resolution display screens from “retina” etc. phone displays to 4K and 8K computer displays and TVs, pixel density (PPI) has soared to measurements of over 200 PPI and even 400 PPI!
These displays, most high-quality digital displays have a good enough PPI to render individual pixels completely invisible.
In today’s digital world PPI is more important than ever because people are viewing images on digital displays more, and less on physical prints.
PPI is especially important for smartphone screens because their resolutions can vary widely. Also, phone screens are relatively small and are viewed rather close-up. (Even though that’s not good for your eyes!) Therefore, a phone with a very high PPI (such as 400+) is often very desirable.
Pixels are very important when viewing images on 4K or 8K monitors, since images that look great on conventional monitors (1920×1080 pixels) can look terrible on a display that is four or eight times the size.
However, note that 4K and 8K are absolute pixel dimensions, not per-inch pixel dimensions. (In other words, you can have a 22-inch 4K computer display and a 32-inch 4Kcomputer display; they will have the same number of total pixels, but a different PPI.)
Tech Fact: For those who are wondering, 4K is just 8 megapixels, or 12 megapixels when cropped from a 2:3 aspect ratio to 16:9. An 8K image will require a ~40-megapixel camera!
PPI Image Resolution VS PPI Display Resolution
Digital images are saved with a PPI resolution, however, when it applies to an image itself, it’s just a number. In fact, the number is actually meaningless without at least one other digital measurement to go with it. Why? Because, just like on a physical display, you don’t just need to know the PPI of an image, you also need to know either the total number of inches or the total number of pixels!
Think of it as a simple math problem with three numbers, where having two of them will always give you the third number through simple multiplication or division.
For example, 300 PPI X (times) 20 inches = (equals) a 6000-pixel wide image!
So, a lot of photographers ask, “what PPI should I save my images at?” The answer is this: As long as the total number of pixels itself doesn’t change, the PPI of an image is mostly just an arbitrary number until you decide to actually print the image out. That’s when you need to worry about how many pixels are available to print, per inch!
What Is DPI?
DPI is a common acronym used to denote Dots Per Inch. In ink-based printing, tiny colored dots of ink are used to create a color image on paper or whatever surface the print is made on; canvas, metal, anything!
If you have ever looked closely at a newspaper, magazine, or large or mass-printed imagery, you may have noticed individual dots arranged in a grid pattern. When you look at the print from a further away, though, the dots blur into rich colors that create a clear image.
The density of the dots in a printed image determines how far away from the print a viewer’s eye must be from the image in order for it to look lifelike. That is, in order for the individual dots to “disappear”.
Usually, on pretty much all photography-related printing services these days, you must literally touch your nose to the print, (or photograph it with an actual macro lens!) …in order to see ink dots.
Of course, higher-DPI printed imagery costs more, so, truly high-quality printing is usually only used for digital photographs and other high-quality forms of visual presentation. On the other hand, lower DPI settings are usually preferable for newspapers and other low-cost, relatively temporary types of printed imagery that are cheap and disposable.
Inkjet Printing Technology
Inkjet printers used to be rather poor quality, just a decade or two ago. They did not offer enough DPI, and also, the inks themselves were not very high quality and would fade very quickly compared to a chemical print made using a darkroom.
Today, inkjet printing technology has advanced significantly. Their DPI measures in the hundreds or the thousands. In fact, they can use digital images with resolutions in the range of 300 to 600 PPI, (we’ll get to that in a second!) …and print them at incredibly high DPIs ranging from 1200 to 4800!
Also, today’s inks have incredible longevity, that is, they will stay nice and colorful for years to come, especially if you keep them out of direct sunlight, of course.
Tech Tidbit: Printing time is another important constraint to keep in mind when considering DPI quality. Inkjet printers can take several minutes to print a full sheet of paper at top DPI settings, or, significantly faster at a much lower DPI setting.
Printing time was/is a major factor in newspaper and magazine printing, since printing presses have only a a few hours to print thousands or even millions of pages. Oppositely, a serious photographer who is only printing one very important photo, whether a portrait or a landscape image, will probably be happy to take the extra time to make the highest resolution print.
PPI vs DPI | RGB vs CMYK
One of the most notable difference between DPI and PPI, when going from your digital display to a printed image, is the base of colors used to render graphics. In DPI-based media, colors are formed using dots in cyan, magenta, yellow, and black. This base of colors is known as CMYK, a format used by most printers.
On the other hand, pixels on a digital display are broken down into red, green, and blue colors, or RGB. There is no grayscale color in digital arts because the “colors” of black or white are formed by darkening or brightening the red, green, and blue colors simultaneously to the same level. (See above!)
Using DPI and PPI in Image Editing Software
When editing your photos, you can indeed change the PPI, but doing so will not magically increase the resolution of your image detail, it will only spread out the existing image data across more pixels. In other words, you can re-size an image from 24 megapixels to 40-60 megapixels, and if the inch dimensions of the digital file remain constant then that would greatly increase the PPI of the image, HOWEVER, you would of course still have the image detail of a 24-megapixel image.
Some tools, such as Photoshop, Topaz Labs, and many others can use AI algorithms to increase an image’s resolution with very impressive levels of detail refinement, effectively making the image appear to have better image detail. However, there are limits to how far image quality can be upscaled, so if you want to make a very large print, it is important to start with a camera/sensor that has a very high resolution.
Do you need to set the PPI on your camera?
No! Cameras generally don’t have a PPI resolution setting. All you have to do is set your image size to the largest, highest-megapixel setting. At the time of capture, PPI does not matter, it’s a setting you’ll worry about later.
When you bring that image into a raw processing application such as Adobe Lightroom, again, PPI will still not be relevant; all that matters is the total pixel dimensions.
When you export your images from Lightroom to JPG, or to Photoshop as a PSD file, then you will have the option to designate a PPI. Sometimes, by specifying both an inch (or centimeter) dimension and a PPI, you will find that your actual image resolution has increased or decreased quite a bit. That’s okay!
Going From Screen to Print | DPI vs PPI Conversion
Finally, when images are printed, special considerations must be taken into account. If an image in a PPI-based format is printed as-is, it could turn out much smaller than it appears on a monitor, if the monitor has a much lower resolution than the maximum resolution that your printer is capable of.
Example: Your computer display is only ~100 PPI, and you viewed the image full-screen instead of paying attention to its PPI, and your image goes to the printer set to 300 PPI. Your print will be 1/3 the size of your computer display!
So when you go to print, first of all, look at both the PPI and the total inch dimensions of your image. You will want the inch measurement to match your actual desired print size, and you will want the PPI measurement to be the maximum that the printer is capable of utilizing.
This may require that you scale or re-size the actual pixel dimensions of the image up or down, but as long as the change is not too significant, yo u will not notice any issues in the final print, and it will appear quite detailed and sharp!
PRO TIP: Remember to apply any sharpening to your image AFTER you have re-sized it! This will ensure the highest possible level of image detail.
Selecting the Right Image Quality
Keep in mind that not all photos need to be printed in top quality. As mentioned earlier, printing a full sheet of paper at maximum DPI settings can take several minutes. If you need to print dozens of copies of several photos, it could take hours to finish printing what you need. Unless you plan on framing your image, and looking at it very close-up quite often, it is unlikely that that top image quality is truly necessary. Scaling down images can also be advantageous in digital media to reduce file sizes and reduce the graphics memory that your images consume. (For example, creating Smart Previews in Lightroom means that your high-megapixel images are edited by proxy as mere ~2 megapixel images!)
Conclusion | PPI vs DPI
In short, it’s all just electronic pixels and dots of ink! Both are very important if you are going to not just capture images and view them full-screen on your computer or phone, but also make physical prints, large or small.
At the beginning of your photography process, don’t worry too much about PPI, let alone DPI. Just focus on capturing your images with the highest possible resolution. (Megapixels)
On most digital displays, you don’t need to worry about adjusting the PPI of your images to fit a display, as long as their total pixel dimensions are long enough to be viewed full-screen!
Once you think about printing, then you’ll want to start by making sure you have the correct PPI (and inch dimensions) for your image. then, finish by ensuring that your printer’s DPI resolution offers as much print quality as possible!