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Image Resolution, DPI, Pixels – What Does It All Mean?

July 28, 2021 (Last Updated August 04, 2021)

Lisa Fulton

When we talk about resolution, we're referring to the dots per inch (dpi) of the graphics. A higher dpi means a higher quality image—so if something is low-resolution, that means it has a low dpi and may print blurry. Especially if you’re searching online for an image, it’s important to check the dpi or the dimensions in pixels if they are noted. To get the best quality, you’ll want to make sure the images you use are at least 300 dpi at the finished size.


How to determine the dimensions of an image

In Photoshop: Open the file to see the pixels and size in inches.


On a PC: Right-click on the file and select “Properties.” Then select the “Details” tab


On a Mac: Right click on the file and select “Get Info.”


If you're scanning images, make sure your scanner is set to a resolution of at least 300 dpi and that you're not enlarging the image too much from its original size.


If you can’t determine the dpi or can’t get a version of the image that is at least 300 dpi, you’re not out of options. While we recommend 300 dpi, it’s often true that 200 dpi is good enough.


Making Sense of the Numbers

Here’s an example. Let's say we have an image that is 240 pixels wide x 160 pixels tall. The width in pixels divided by our desired resolution (dpi) will give us the maximum width in inches before the image becomes low resolution.


(Pixels ÷ Desired dpi = Maximum Size in Inches).


So, we take the 240-pixel width and divide this by the 200 dpi quality we’d like, which gives us 1.2 inches (240 ÷ 200 = 1.2). This means the photo will be blurry or low resolution if it’s larger than 1.2 inches. But at 1.2 inches wide, it’s acceptable quality and ready to print.


240 Pixel Image


We know what you’re thinking: 1.2 inches is way too small. If you need an image to be a specific size, you can find out what resolution it will be at that size by using a formula similar to the one above. The width in pixels divided by the desired width in inches will give you the resolution at that size.

 (Pixels ÷ Inches= dpi).


So, let's say we want this image to be 4 inches wide to be centered on the front cover of our book. We take the 240-pixel width and divide this by the 4-inch width we want, which gives us a dpi of only 60 (240 ÷ 4 = 60). This means if we're enlarging the image to 4 inches, it will look pretty blurry when printed (and even looks blurry on screen):


Enlarged 240 Pixel Image


If you have access to a larger or higher resolution version of an image, you have a better chance of getting it to look the way you want. Unfortunately there’s just not a way to improve the quality of an image if it’s low resolution to begin with. Luckily, our photographer was able to send us a version of the same image that is 800 x 533 pixels.


800 pixels divided by 200 dpi (the lowest dpi we want before we risk losing quality) = 4 inches (800 ÷ 200 = 4). This means we can make the image 4 inches wide or smaller and it will be good quality when printed, though not perfect.


We're much happier with the way this image looks, even though it’s still not the recommended 300 dpi.


800 Pixel Image


If we wanted to ensure beyond all doubt that the picture would print perfectly without having to re-size it, we’d need to find a version of the image that was at least 1200 pixels wide. (If you’re catching on, you’ll know that we found this by multiplying our desired 4-inch width by our desired 300 dpi resolution (4 x 300 = 1200)).


Here are those formulas again:

Pixels ÷ dpi = Maximum Size in Inches


Pixels ÷ Inches = dpi


Inches x dpi = Width in Pixels Needed


Crunching the numbers and trying to figure out image resolution can be a real headache, but it’s an important step in getting your book to look the way you want. High resolution images make your book look much more professional, and it’s worth the extra time and effort to get a great looking final product! If you ever have questions about regarding your files before you place an order, call us at 800-231-0521 and our team will be happy to answer all of your questions!


Contact us today!

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