Dots Per Inch (DPI) vs Pixel Per inch (PPI)? What is the Difference?

Whenever DPI and PPI get into the conversation, a great amount of confusion arises. The people aren’t the one to blame because these terms are always interchanged by error. So what are their differences and what effect do they have on digital images and printed photographs? Keep reading to find out!

What is DPI?

Dots per inch, or DPI, represents the printer’s resolution. It’s basically the density of ink dots that falls into the sheet of paper or whatever medium you use. A key point here is DPI purely talks about the printer and it does not have any correlation with what happens digitally.

What is PPI?

Pixels per inch, or PPI, refers to the digital image resolution, not a print. It is used primarily for image resizing before printing. To have a full understanding of PPI, we have to first understand what a pixel is. 

Picture element, or a pixel, comes in squares and is arranged on a grid. They are the very basic and smallest components of a digital image. Each square comes in different hues and these squares are so small for our eyes to see. In essence, our brain automatically sees the bigger picture where these squares are perfectly blended and smooth. But hey, before the technical dudes call me out, we know that is not entirely correct. The pixels come in sub-pixels of red, green, and blue, which blend together beautifully. 

Size of the digital image

It’s your camera that first dictates the size of your image. This is largely dependent on your camera and the way you’ve set it. A Fujifilm X-T2 can capture a file that is 6,000 pixels x 4,000 pixels in raw form. If I opt to set my camera to produce a JPEG file, I can choose between three size options: large (L) for 6,000 x 4,000 pixels, medium (M) for 4,240 x 2,832 pixels, and small (S) for 3,008 x 2,000 pixels.

You would also have some mathematics to do to fully grasp this. For example, for a large JPEG file, 6,000 multiplied by 4,000 is 24,000,000 pixels. If shortened, this is 24 MP (million pixels or megapixels). So if you’re on the lookout for a camera and you find one that it’s a 24MP camera, this is what it means. Although there are more things to learn about camera resolution, we don’t have to get down to those in this article.

Screen resolution and PPI

PPI also refers to the screen resolution. Take note that screen resolution and digital image resolution are completely different things. The resolution in your screen is a fixed value, thus, it does not change from time to time. For example, a 15” MacBook Pro Retina boasts of a screen resolution of 2,880 x 1,800 pixels with a resolution of 221 PPI. On the other hand, an iPhone X has a 1,125 x 2,436 pixel count with a resolution of 463 PPI. Higher display resolutions mean smaller and more closely packed device pixels. The higher the display resolution is, the sharper and crisper the display is. 

Take note that image resolution has no effect on how a photo will display on the device since the pixel count is fixed. In other words, you can easily export a 72 PPI, 96 PPI, or 5,000 PPI image but you may see the same thing on your device depending on its pixel count. In a display screen, it’s the picture size that dictates how the image will look rather than the image resolution.

Print size and PPI

Majority of the confusion lies in this topic. But a simple way to remember it is: DPI does not apply to digital images! DPI is solely correlated to printers rather than the digital images.

PPI basically describes the number of image pixels present in the digital image which will be utilized to create an inch on the print. Again, math comes in handy for this. Simply divide the pixel dimensions of the image by the resolution. Therefore, should I print a 6,000 x 4,000 pixel image file for my Fujifilm X-T2 a 200 PPI, the computation would be a simple 6,000/200 = 30” in length and 4,000/200 = 20” in height.

Please do not get confused. There’s no such thing as pixels in print. Take this: Each image pixel present in the digital file will be printed a small square on the photo paper so let’s call it a “paper pixel.” Each paper pixel holds the same color tone as that in the corresponding pixel of the digital file. Now, try to go to the Image Size box on Photoshop. Try changing the resolution and you’ll see that the pixel dimensions remain constant. It remains to be 6,000 x 4,000. Also, the file size of 137.3 megabits does not change as well. It is the width and the height that changes. 

To try to make it simpler, think about the pixel number in your digital photo as an icing can. It comes with a fixed amount of icing inside but it’s up to you how you want to spread it on top of the cake. You may apply it thinly to fill a big, rectangular cake, or you may pile it up coarsely on a small cupcake. The bigger your cake is, the more spread out the icing is as well which is comparable to smaller PPI value resulting in a big but low resolution print. On the other hand, a small cupcake will have a highly dense layer of icing the same way a large PPI will give you a small but a high-resolution print. 

How huge can my print be?

A lot of printing shops recommend a 300 PPI resolution for a nicely printed photo. To compute, the image dimension should be divided by 300 to get the biggest possible print. Utilizing our X-T2 example, 6,000/300 = 20” in length by 4000/300 = 13.33” im height. This is how to calculate for the biggest ideal size to maximize the beauty of the photo.

But, it is also completely okay to print it larger, but you have to understand that the bigger you go from the ideal size, the lower the resolution will be. Take this: a 300” x 200” is actually billboard size with 1.3 mm wide paper pixels. If you view this billboard from far away, it will look smooth. But once you try to get closer and closer, you will start to see the jagged components or the largely spaced print pixels. Should you want a large print of 16” x 20” to hang to your wall and are usually several feet away, a resolution of 200 or 240 PPI will do just fine. 

The print material also matters. Let’s say you want to print on a glossy surface, the resolution should be higher for this to ensure a crisp and a sharp image. Meanwhile, printing on canvas requires a relatively lower resolution because of the medium’s texture.

Also, to maximize the quality of your photo and the size of your print, make sure to set you camera to take photos as large as possible!

Resampling

Have you ever tried having a photo printed but it does not have enough pixels for the print size you want? Then resampling is the way to go. Resampling is the process of adding pixels to a photo file. But take note that this is not highly recommended because the image quality suffers significantly. 

For resampling, you may use a software such as On1 Resize. This resampling software takes guesses based on the surrounding pixels. Here, spreading out of the original pixels as they are replaced with new ones fill in the gaps.

Resampling does not only add pixels, it can also decrease them. Downsizing is especially used if the images are only needed for the world wide web. Why do we need to do it? Downsizing makes the photo and the article in general load faster. But, keep in mind as well that even downsizing can degrade an image because you’re essentially taking some of its pixels away. 

DPI in a nutshell 

Lastly, let’s now touch base with dots per inch. As opposed to PPI, DPI does not come in squares. It comes in tiny dots of ink which the printer creates by spraying droplet inks on paper. To form one single pixel, it takes a lot of dots to do so.

There are printers in the market that allow you to customize the settings so you can control variables such as the ink density, but for most of the printers we have at home, the printer’s resolution is fixed. The choices are simpler with our home printers, usually in normal, best, draft, or photo. They vary as to how closely the small dots are sprayed on paper. Inkjet printers are known to hold 300 to 720 DPI of resolution. Laser printers can go up 2,400 DPI and more. 

You have to remember that DPI is a printer function rather than a variable you get to adjust in photo editing apps or softwares. 

Final words

To summarize, the smallest building block of a digital image is what we call a pixel. Pixels come in squares that are applied on a rectangular grid. With this said, pixel count, also known as the image dimension, is the pixel numbers spread all throughout the digital photograph.

PPI refers to the digital image resolution which has the capacity to determine the print size. On the other hand, DPI is a printer function determining on how closely the tiny dots are sprayed on the print medium.

If you made it here, congrats! You are now a bit smarter than the rest of the world. It helps to not get confused between the two! 

FAQs