The printing size is governed by the document size in inch or millimeter. The PPI will affect the final printings if it is not set correctly. In a nutshell, PPI is about how many pixels you get in an inches and that is pretty basic about it. When people go to print, they will most probably say the size of the printing in inches and millimeters, not pixels because pixel is simply the smallest value that represents a graphic in digital form. Therefore, pixel is not the right value to measure a size of the printed document.
For high quality printings, the rule of thumb is to have it set at 300 ppi versus the actual size of the printing. Meanwhile, as for banner quality printing, it is recommended to set the ppi from 100 to 150 due to the distance it is viewed.
PPI's Difference at 4" x 4" Prints
Here, I'll show you the difference of quality at different ppi for the same image and size, which would be a 4" x 4" in the final print. The example you about to see will be setup at 50, 72, 100 and 300 ppi respectively so that you could clearly identify their difference in terms of quality.
Changing PPI without ResamplePPI's Difference at 4" x 4" Prints
Here, I'll show you the difference of quality at different ppi for the same image and size, which would be a 4" x 4" in the final print. The example you about to see will be setup at 50, 72, 100 and 300 ppi respectively so that you could clearly identify their difference in terms of quality.
The muffin photo is taken using my 8MP phone camera and it gives 3264px x 2448px. For best viewing quality as you would normally see in magazine. It can be printed at 10" x 8" without any problem.
If the resolution is changed to a very low value (eg 1ppi), you would notice that the pixel value does not change. However, you would notice that the document size is now 3264" x 2448" as oppose to 10" x 8" at 300 ppi. Printing the image directly will end up in a very pixelated and low quality printout.
Why Bother About The PPI When Pixels Remain The Same?
When you send your file for printing, having the file size and ppi set correctly do make a difference. It's really a time saver and avoids unnecessary mistakes. Everything can be printed right away with a snap of finger.
Imagine that you have 100 photos and the file size and ppi are totally messed up. Because for some reasons, you just do not care about it. The operator will have to open the file and resize the photo and resolution for you and that is just 100 photos. What if there were 10 people and each of them have 100 photos needed to be printed? It would be frustrating.
I hope this tip is beneficial to all professionals whether you are a designer, photographer or maybe even home users. Do yourself and everyone a favor and makes your prints and photos print-friendly. If you have question, feel free to ask me or you may tell me what you think about it.
