Photography Tutorial - PPI and DPI

PPI (Pixels per Inch) and DPI (Dots per Inch) are confusing to many of photographers because of their interchangeable usage across the media and the internet. In fact, PPI and DPI are two different things and they are the domains of two different professionals. PPI matters for web designers, graphic designers, video editors or anyone who uses Photoshop or any editing software while DPI matters most to printing firms.

When you take a picture on your smartphone or Digital Camera. It says how many megapixels it is. Right? That is the resolution of the image. 16 MP Camera, for example, produces an image with 16 million pixels, likewise, 8 MP Camera produces an image with 8 million pixels. But, then where is PPI. PPI is different from Megapixels of a camera. PPI can be set to 72 or 300 in your camera, but it is not going to make any difference to your image.

So, what is PPI?, PPI is simply the number of pixels in your image. If you zoom in close to any image (see the picture below of a woman's eye), you will see squares of different colors which are called pixels. When you see more of these square even at normal zoom, the image is called pixelated because there are few pixels per inch in the image. It also does not mean more PPI will give more quality because most monitors available in the market are between 72 PPI and 120 PPI. So, even if the image is of 300 PPI, a monitor cannot display that. Some of the latest retina displays have more than 200 PPI and these can show more pixels on your monitor, otherwise most monitors are limited to 72 to 120 PPI.

Most of the time, 72 PPI is more than enough unless you are planning to print it. If you are planning to print, you can change the PPI manually in any editing software by entering the new value. One thing to note is that unless you resample the images (Increasing the actual dimension of the image), more the PPI, smaller your image will be during print. Because, now there are more pixels per inch and printer need to incorporate all those pixels while printing, similarly if we reduce the PPI in editing software, then there are number of pixels to work with and the printer will print it in a larger size though in this case, pixelation would be more visible.

DPI (Dots per Inch) matters only to a printer and if you are not planning to print it yourselves, you can ignore it. Let's illustrate this with an example. If you are having a 1200 DPI Printer, it uses 1200 dots of ink per every inch, if you are having 1500 DPI printer, it will use 1500 dots of ink per inch.

Relationship between PPI and DPI