This guide outlines how to tell the DPI of an image in Windows, Mac OS and with other methods.
When working with digital images, it is important to understand image resolution, which is an indicator of quality. Resolution is the relationship between the number of dots, pixels or lines that exist in an image in relation to the size at which it will be reproduced in the real world.
Resolution can be measured in DPI (Dots Per Inch), PPI (Pixels Per Inch), or LPI (Lines Per Inch… mostly only used by professionals). For most everyday uses, DPI is the usual measurement.
In this guide, we will explain how to tell the DPI of an image, and what DPI (and PPI) are.
What is DPI? DPI is a measurement that indicates the number of ink dots printed in one inch. The higher the DPI number, the higher the quality and sharpness of the printed image. However, it is important to point out that DPI is only relevant for images that will be printed, not for digital images displayed on screens.
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How to tell the DPI of an image
There are several ways to find out the DPI of an image. Let’s look at some options.
How to tell the DPI of an image in Windows
In Windows, you can check the DPI (dots per inch) of an image by viewing its properties. Here’s how you can do it:
- Navigate to the folder where the image is saved.
- Right-click on the image file with your right mouse button to bring up a contextual menu.
- From the contextual menu, choose “Properties” at the bottom. This will open a dialog box with information about the image.
- In the Properties dialog box, there are different tabs. Click on the “Details” tab.
- Scroll down within the Details tab to find the “Image” section.
- In the “Image” section, you should see information about the image dimensions as well as the DPI (dots per inch) value.
Note: If the DPI information is not directly listed, you may see the dimensions in pixels (e.g., width and height). To calculate the DPI, divide the pixel dimensions of the image by its physical dimensions (in inches). For example, if the image is 1200 pixels wide by 800 pixels high and is 4 inches wide by 2.67 inches high, the DPI would be calculated as follows:
DPI (horizontal) = 1200 pixels / 4 inches = 300 DPI
DPI (vertical) = 800 pixels / 2.67 inches ≈ 300 DPI
How to tell the DPI of an image e in Mac OS
To check the DPI (dots per inch) of an image on MacOS, you can use the Preview app, which comes pre-installed on every Mac.
- Navigate to the folder where the image is stored.
- Right-click on the image file with your secondary mouse button (two-finger click on a trackpad) to bring up a contextual menu.
- From the contextual menu, choose “Open With” and then select “Preview” from the submenu. Alternatively, you can simply double-click on the image file to open it with Preview.
- With the image open in Preview, go to the “Tools” menu in the menu bar at the top of the screen.
- From the dropdown menu under “Tools,” choose “Show Inspector” (or simply press Command + I on your keyboard). This will open the Inspector window.
- In the Inspector window, click on the “Exif” tab. This tab shows metadata information about the image, including its dimensions and resolution (DPI).
- In the Exif tab, you should see information about the image resolution, including the DPI (dots per inch) value.
If you don’t see the DPI information directly listed, you can calculate it by dividing the pixel dimensions of the image by its physical dimensions (in inches) with the formula we have shown in the Windows section above.
How to tell the DPI of an image using image tools
In some image editing programs, such as Adobe Photoshop, you can view image information, including DPI. Just open the image in the program and access the properties or information.
How to tell the DPI of an image using online tools
There are several online tools that allow you to check the DPI of an image. Just upload the image and the tool will provide you with the information including the DPI.
It’s important to remember that even if you find out the DPI of an image, it doesn’t mean you can increase its quality or resolution. DPI is related to the number of dots printed in an inch and cannot be changed without loss of quality.
Using DPI and PPI to send to output devices
DPI (Dots Per Inch)
This is the usual specification for the resolution of output devices such as desktop printers, film recorders, imagesetters, etc.
Whenever we work on the computer for something digital, the base ratio of the file’s PPI in relation to the printer’s DPI is 1:1, i.e.
For computer monitors and movie recorders, there is a 1:1 ratio between the PPI of the digital image file and the DPI of the output device. In other words, in this situation, an image with 300 PPI is the same as an image with 300 DPI.
But in other cases like typical desktop inkjet or laser printers, today there is a big difference between DPI and PPI. In an inkjet printer, say, 2880 DPI resolution, many micro dots of ink are used to construct one pixel of the image i.e. approximately 92 dots (9.6 width x 9.6 height) to constitute 1 pixel. This is why we often cannot differentiate with the naked eye the difference between a print at 1440 DPI and a print at 2880 DPI.
PPI (Pixels Per Inch)
A pixel is the smallest unit and the smallest point that can be reproduced on a screen — a monitor, projector, cell phone, tablet, etc.
A screen is divided into a matrix of thousands or millions of pixels, because they are so small, you can’t see just one with the naked eye. Each pixel can only take on one color at a time, but when a set of pixels of several different colors come together, we can see images, textures, and variations in brightness and shadows, that is, images. Whenever we talk about pixels we are talking about a measurement in the digital world.
When we are using software like Photoshop, Illustrator or CorelDRAW for example, they allow us to know how many pixels the image has. So, in order to measure the size and reproduction quality of this image on a physical material, we calculate (or rather the software calculates) how many pixels of this image there are in one inch (one inch = 2.54cm).
Let’s say we have an image that is 4 inches (10.16cm) wide x 4 inches (10.16cm) and that it is 1200 pixels wide x 1200 pixels high. So it will have 300 pixels per inch or 300 PPI.
Whenever we talk about commercial printed materials, catalogs, books, magazines, advertisements, flyers, folders, any image you use in the material, it has been agreed that the ideal resolution is 300 PPI for the image in the size in which it will be reproduced, that’s ok. if it has a little more resolution, the problem is less. But if the image is 299 PPI? Well, you don’t fight for 1 cent in 1.99 stores, you shouldn’t bother fighting for 1 PPI, but the ideal is 300 PPI, ok?
But why don’t we make files with 2880 PPI to be used on a printer with 2880 DPI? Because this file would actually be very huge and it would be unfeasible nowadays to send such a file over the internet, so the printer’s own software does this work when processing the print.
Conclusion
We hope this guide has clarified how to tell the DPI of an image, and explained how to use the DPI and PPI.
Photo by Jenna Hamra
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