What to Know About Digital Image Sizes, DPI, and PPI
What is DPI? What is PPI? Are DPI and PPI the same? If you’re confused by image size terminology, that’s no surprise. These terms from pre-digital image days are still used to describe our digital image world.
It’s easy to be confused about image sizing. Understanding digital image sizes requires a deep knowledge, but you don’t have to know much to be competent enough to make smart decisions about your family photos.
What to know about digital image sizes, DPI, and PPI
DPI = Dots per inch
DPI is used to talk about (and comes from) printing, where small dots of ink are put on paper to create an image. So when you’re printing images or looking at a printed image, you’re talking about DPI.
Lower DPI means bigger dots. Look at a printed photo in a newspaper with a magnifying glass. You can see the dots. 72 dpi, used in newspaper printing, is considered low resolution dpi.
Higher DPI means smaller dots. Look at the photos in a coffee table book with a magnifying glass. You’ll be hard pressed to see the dots, and if you can, you’ll see the size difference with a newspaper’s photo dots. 300 dpi is considered standard dpi for printing.
PPI = Pixels per inch
PPI is used for determining the size of a digital image by measuring along its width and height. So, when you’re talking about PPI, know that you’re talking about a digital image.
The standard (72 ppi) is what is created by most digital cameras and phone cameras. That size means images load quickly on a computer screen but are often too small for quality printing.
Resolution is the density of image data. For both DPI and PPI, a higher number DPI and PPI is equal to greater detail and larger images.
Image file size is the key for preserving tangible images. Larger file sizes allow for larger prints and can always be reduced for web use if necessary. Your file size for an image should be a 1 MB (megabyte) minimum.
Maintain a minimum 300 dpi/ppi resolution and 1 MB file when scanning
In scanning tangible images (prints, slides, negatives) to digital images, the size and material of the original piece are important factors. Maintaining a minimum 300 dpi/ppi resolution and yielding a minimum 1MB scan is the goal. Therefore, smaller prints should be scanned at a higher resolution, as should slides and negatives, to ensure a proper size file and resolution to give the most flexibility for future use, like creating an 8”x10” print from a 2”x2” original print or slide.
A smaller PPI works fine with a smaller image, but if you ever want to view or print it larger, it’s not suitable. © Pixorium
If the resolution (density of image data) isn’t high enough, the image will pixelate as you make it larger. You’ve probably had this experience when printing photos from your phone at a drugstore photo center. The photo looks great on your phone, but when you print it, it’s pixelated. This is because the 72 ppi resolution of your digital image wasn’t high-enough quality to print a clean image like the 300 dpi pictures you see in books.