DPI, PPI and print resolution, explained simply

A photo on a screen and a photo on paper are made of different things. On a screen, light glows through tiny squares called pixels. On paper, ink sits in tiny dots. Resolution is simply how many of those pixels you have to spread across each inch of the printed page. Get that number right and your photobook looks crisp in the hand. Get it wrong and faces go soft, the writing on signs smears, and fine details like hair or leaves turn to mush.

The good news: you do not need to understand the maths to get it right. You need to remember one number and know how to check it.

What is the difference between DPI and PPI?

PPI means pixels per inch and describes your digital photo. DPI means dots per inch and describes the printer. People use them interchangeably, and for planning a photobook that is fine. When a print service asks for "300 DPI", it really means: give each printed inch at least 300 pixels of your photo.

How many pixels do I need for a sharp print?

Aim for 300 pixels per inch at the size the photo will be printed. Between 200 and 300 still looks good to most people at normal reading distance. Below about 150, softness becomes visible, especially in faces and fine patterns.

To work out the largest size a photo can print well, divide its pixel width and height by 300. A photo that is 4000 by 3000 pixels prints sharply at about 13 by 10 inches. The same photo stretched across a 24 inch wide spread drops to around 167 pixels per inch, which is where you start to notice.

Photo size in pixels	Sharp at 300 PPI	Fine at 200 PPI
2000 x 1500	6.7 x 5 in	10 x 7.5 in
3000 x 2000	10 x 6.7 in	15 x 10 in
4000 x 3000	13.3 x 10 in	20 x 15 in
6000 x 4000	20 x 13.3 in	30 x 20 in

Does cropping reduce print quality?

Yes. Every crop throws pixels away. If you crop a phone photo down to a single face and then stretch that face across a full page, you are asking a small number of pixels to cover a large area. Crop with your final size in mind: a tight crop is fine for a small photo in a grid, but keep the full frame for anything that will run full bleed.

Why do photos from messaging apps print badly?

Most chat apps compress photos to save data. A picture sent over a messenger can arrive at a fraction of its original size, and once the detail is gone it cannot be added back. If a friend sends you the perfect photo for your book, ask them to share the original file through a cloud link, as an email attachment sent as a document, or over a cable. The same applies to screenshots and photos saved from social media: they are fine for small spots, not for full pages.

Can I upscale a low resolution photo?

Upscaling software can make a soft photo look smoother, and modern tools are surprisingly good at it. It cannot recover real detail that was never captured. Use it as a rescue for one important photo, not as a plan for a whole book. Where you can, choose a different shot or run the soft one smaller.

How Soouvenir helps

Every photo you add keeps its full resolution. As you place and resize it, the editor checks how many pixels per inch it will print at and warns you before a photo would print soft, so you can shrink it, swap it or keep it with your eyes open. Nothing is quietly downsized.

A quick checklist before you print

• Use original files from your camera or phone gallery, not copies from chat apps.
• Save your biggest, sharpest photos for full pages and spreads.
• Run cropped or older phone photos smaller, in grids or as supporting images.
• Zoom to 100 percent on your screen and look at faces. If they look soft there, they will look soft on paper.
• Treat warnings as advice, not rules. A slightly soft photo of someone you love still belongs in the book.