Photo quality, resolution, dpi/ppi

I was working on poster for our living room. So I needed to find out if photos I downloaded from internet was good enough for printing.

There are two units of measurements for photo quality. DPI (dots per inch) and PPI (pixels per inch). DPI is usually used for printing devices and PPI is used for imaging devices such as cameras and scanners. As picture editing softwares usually use PPI, I'll use it.

As I've mentioned PPI gives you there are how many picture cells in the inch of a photo. And for a good quality print it should be 300 ppi. If you right click to an image file and open it's properties you will see that dimensions are given in pixels. So consider you have a picture with dimensions 3216x2163 pixels.

If we divide this dimensions by 300, we will find the optimal printing size for this picture, which is 10,7x7,1 inch or 27x18 centimeters. Now we know that if we would like to have a print out of this photo to an A3 size paper, the end result will be a poor.