Printers and computers see and present images very differently. One of those details is the image size. When you say you need an image at 72 ppi, that could mean a lot of things! You can have an image that is 1 pixel by 1 pixel at 72 ppi – that’s pretty darn tiny! Hint, it’s the little dot above the caption.
You could have an image that’s 792 pixels by 1224 pixels at 72 ppi, that is the same size as an 11 x 17 piece of paper. If you have an image that big, you’d think you can print it at poster size without any problems, right?Wrong! Professional printers (as compared to your home printer) need images that are at 300 dpi to print. Fine point here – last paragraph I wrote ppi, this paragraph is about dpi. The difference is, ppi is based on pixels on a screen. Screen resolution varies from your cell phone to a huge projection TV screen. The pixels on a projection screen are much larger than those on your phone or computer. Dpi is based on ink drops, which are pretty much all the same size relatively speaking. We’re not talking Jackson Pollock, we’re talking about ink on a press. When you look at a printed piece under a good magnifying glass, you will see the little dots. It takes about 4 times as many dots per inch to print an image as it does pixels per inch to view it on screen.
Here’s what you see on a black and white image, the dot pattern of the dog photo is the printed black ink dots.
So finally, this is the difference between high resolution and low. That 11 x 17 image at 72 ppi translates to 2.64 x 4.08 inches at 300 dpi. 300 dpi is a typical resolution that a printer needs. So when your printer says your image that you think looks good on your computer is too small to print, you now understand that he need an image 4 times larger than what you are looking at on screen to print it at the same quality.
Next lesson, RGB vs CMYK.


