Understanding Resolution for Digital Photography, Graphic Design and More

"300 DPI."

"1500 X 1500."

These terms all appear different, but they all refer to the same thing. Resolution. So it's no wonder many people are confused by the details of resolution. If you are interested in digital photography, graphic design, or selling your own t-shirt designs on the internet, it's important to have a grasp on the concept of resolution so your images look professional. Read on for a crash course in understanding resolution.

You have probably seen the term 72 PPI. Most computer monitors display images at a resolution of 72 PPI or pixels per inch. That means that every square inch on your monitor contains 72 pixels. A pixel is a tiny little square of light, and thousands of them are combined to make the images you see on your screen. Most monitors are not capable of displaying more than 72 PPI, so most images you see on the internet will be optimized for display at that resolution.

If you have ever downloaded an image from the internet and printed it, you may have noticed that when it came out of the printer, it didn't look that great. It probably looked jagged and blurry. That's because in order for an image to look good on paper, it needs to be printed at 200-300 DPI. DPI and PPI are basically the same thing, except that DPI stands for dots per inch, and refers to the printed resolution of an image.

PPI=Pixels per inch and refers to screen resolution.

DPI=Dots-per-inch and refers to printed resolution.

That's easy enough to remember. But there is a third way of referring to resolution and that is the images' total size in pixels. If an image is 1500 X 1500 that means that it is 1500 pixels wide and 1500 pixels tall. Those numbers are fixed, meaning that unless you crop the image or add more space, it will always be 1500 X 1500. DPI and PPI are arbitrary. If you upload that image to display on a website at 72 PPI, it will be nearly 21 inches wide and 21 inches tall. (1500/72 = 20.83) If you print the image and select a print resolution of 300 PPI, it will be 5 inches wide and 5 inches tall. (1500/300 = 5)

You can make that image any DPI you want. You can smash all the pixels together and make the image one inch by one inch at a resolution of 1500 DPI, or you can spread them apart and make the image 1500 inches by 1500 inches at 1 DPI. That means that your image would be 1500 inches wide and 1500 inches tall, and only have one dot per inch. Naturally, neither of those resolutions would look very good, but it is helpful in demonstrating that you can change the DPI all you want, but the 1500X1500 stays the same.

Another example, imagine you have 50 marbles, and you pour them all inside a small baking pan that is four inches square. They will be bunched together and probably all touching each other. Now you take the marbles and dump them in a large twelve by fifteen baking pan. They are now spread out and not touching each other. The important thing to remember is that no matter how close together or spread out they are, you still only have 50 marbles.

So, you got a brand new high mega-pixel camera for your birthday, and you want to show off the pictures you took with it on a website. You upload them onto your computer and open them in your image editing program. Looking at the image size, you see that they a huge! 2000 X 3000 pixels. You can't put them on the internet like that, because they'll take too long to load, and they'll fill the whole screen. Anyone who looks at them will have to scroll down and sideways to see the whole image. You will need to down sample the image, which means you will need to throw away some pixels. The process will vary depending on your software, but usually there is an image size function, where you can type in your desired size and specify that you want to resample the image. If you enter in 200 X 300, the rest of the pixels will be discarded, and you will be left with an image that is 200 X 300. On the internet this will display a little larger than 2 inches by 3 inches, which is much more manageable e than your original file. But make sure you save a version of your large file, that 2000 X 3000 image is perfect for printing out a nice 8X10 photo!