What is PPI?
PPI stands for Pixels Per Inch. PPI is a measurement of pixel density. The more PPI that a photo has the higher quality it will be. The image will be more smooth, less pixelated or jagged looking. The higher PPI the smaller the pixels are. Each pixel is a small square dot. So the more square dots you put in the same 1 inch will make them smaller. If you have 8 PPI that means each pixel is an 1/8 of an inch (0.125″), imagine making up a photo of 1/8 inch (0.125″) dots, it would look pretty jagged and pixelated. Now think of a photo made up of 200 PPI, which would be 1/200 of an inch (0.005″) dots. The photo would look a lot smoother and you wouldn’t be able to see each individual pixel.
How Many Pixels Per Inch Should I Print My Photos?
You may wonder what are high quality prints PPI set at? Most of your professional work like magazines are printed at 300 PPI to create a high quality print. This PPI is not always needed as some DSLR camera’s sensors are better than others and you can get a high quality print from 200 PPI or even 150 PPI. For example you may take a low end DSLR camera and have to print at 300 PPI to get a high quality photo print, but you could take the exact same photo with a higher end DSLR camera and print at 200 PPI and get the exact same photo print. You also have to think of what size photo print you are printing. If you are printing a 4×6 photo you will be viewing it up close and see more detail. If you are printing a 20×30 photo, you will not be viewing that photo as close as you would the 4×6 photo, so you will see less details. So I always use this as a general rule, but it can change. I always tell photographers to take a few photos with their DSLR camera, print them at home or at a lab, and look at them to see what is acceptable and what isn’t.
Pixels Per Inch or PPI changes to a photo will effect it’s print size. If you have a 100×100 pixels photo and you print it at 100 PPI you will have a 1 inch x 1 inch photo. If you take the same 100×100 pixel photo and print it at 50 PPI you will have a 2 inch x 2 inch photo. The formula is: Pixels / PPI = print size in inches.
What is DPI?
DPI stands for Dots Per Inch. A dot is similar to a pixel, but a pixel is 1 solid color, a dot is actually made up of 4+ colors from your printer. Some printers have more colors of ink to use than others. Your printer can’t create a purple dot to print your purple pixel, so it uses several red and blue dots to create that 1 purple pixel. Usually the higher DPI printers have a higher quality, but this isn’t always the case as one printer manufacturer’s dots maybe different shapes than another printer manufacturer’s dots. General rule though is higher DPI is higher quality prints.
Example if you have a 2400 DPI printer and you are printing a photo at 300 PPI then you would (2400 DPI x 2400 DPI) / (300 PPI x 300 PPI) = 64 dots of ink per pixel.