DPI made simple: why scan quality is important to restore photos

Scanning is the first step in the journey of restoring an old photograph to its former glory. It sounds simple enough – put the picture in the scanner, press go then email it to the team at The Photo Restoration Center. Done. Yet, there’s a little more to it if you want the highest standard of photo restoration.

The quality of the original scan has a direct impact on the final printed product, so it’s important to get it right. Our resolution calculator makes it easy to determine the correct DPI for your scan. “But, what’s DPI?” We hear you cry.

This guide to the basics will help get your scan right first time:

What is DPI?

DPI stands for ‘Dots Per Inch’. It’s a term used to describe the resolution (or clarity) of a printed image and refers to the number of physical dots of ink on the page. Each dot is made up of approximately four to six colors mixed together to create the detail of the image. The higher the DPI, the more dots there are, and therefore the better tonality and smoother color.

For example, have you ever looked closely at a photograph in a printed newspaper? You will often be able to see that it’s made up of a series of individual dots in differing shades of gray. This is because newspapers are printed at a low DPI, so the dots are bigger and there are less of them.

DPI vs PPI - Print vs Digital

DPI vs PPI – Print vs Digital

This is often the part that has people scratching their heads. And, with good reason too. Software manufacturers, professionals and regular folk regularly use the term DPI interchangeably with the term PPI and this causes confusion.

PPI is like DPI’s digital sister. It stands for ‘Pixels Per Inch’. Pixels are the tiny squares that make up the elements of the image you see on a digital display device, such as a computer monitor, tablet or cell phone. They’re a similar concept to the dots on newspapers, but will be seen on a screen rather than in printed form.

is DPI important to restore my pictures?

Why is DPI important to restore my pictures?

DPI is important right from the start of the photo restoration process because it will determine the size and quality of your final printed image. DPI quality is fixed from the point of scan, so cannot be changed via image editing software. This means that if you want to print your restored photograph and the DPI is too low on the original scan, it will look blurry.

But, my imaging software has an option to change the resolution after I’ve scanned it…

Yes, it’s true that Photoshop and similar packages have an option to change the resolution on the digital version of your image after it’s scanned. But, the truth is that increasing the image size in this way isn’t a great idea for a photo restoration project. With this function, the software will stretch the image to the requested size by increasing the number of pixels. The computer estimates the color and intensity of the additional pixels, by using the data of the original image.

This image resizing process is called interpolation. It’s a powerful tool and can be very useful. However, interpolation can never add detail to an image which is not already there. It can only make a best guess to fill in the gaps in data. For the highest quality photo restoration, it’s essential we work with the detail of the original image. Hence why a higher DPI scan is required to achieve the best final product for your image.

From Screen to Print

A printed image may look low quality even when it appears to be good on the computer screen. This is where the difference between PPI and DPI comes in. How something looks on screen can be deceptive.

Your computer monitor has a fixed number of pixels – probably something like 72 PPI. The same image scanned at different DPI resolution will appear the same on the screen because you’re viewing it at this fixed PPI. For example, an image file scanned at 300 DPI and then again at 1200 DPI will likely look the same to you. However, the information in that file will be different and that’s important when you come to print it out.

From Screen to Print

Image: By Wapcaplet, improved anonymously (2014) – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=324587

TAKEAWAY: DPI is specifically related to the printing of an image. It cannot be amended effectively after the original scan, so needs to be high from the start of the photo restoration process. No matter how it looks on the screen, the DPI of the scan will affect the final quality of your restored photograph when printed.

What DPI or resolution setting do I need on my scanner?

This will depend on the size you’re planning to print your final restored photograph. We recommend printing restored photos at no less than 600 DPI. However, if you want to enlarge the printed version, you’ll need to scan at a higher DPI.

Don’t worry, our simple resolution calculator will do the math for you.

Ready to get started? Check out our tips on how to scan for photo restoration and request a quote today.

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