Back to Basics: Resolution Simplified, Part 1

Unlike camera resolution, that measures pixels as a fixed number, image resolution is measured in pixels-per-inch (or ppi) and changes with the size of your photo.

For example, imagine a 4×5-inch digital image on a piece of rubber. If you stretch the rubber to an 8 x 10 inch size, each of the pixels in the image gets bigger. If you keep increasing the size of the photo by stretching even more, pixel sizes will continue to increase until you can see each individual pixel, resulting in an image that looks jagged and blocky.

To look at it another way, it’s like viewing solders in a tight formation from the air. They all look nicely packed together. But if they begin to spread out to occupy a larger space, their number stays the same but you begin to see the more space between them.

Let’s say that at 4 x 5 inches, 300 pixels were lined up along each inch of the rubber print, resulting in 1200 pixels on the 4-inch side (4-inches x 300 pixels) and 1500 pixels on the 5-inch side (5-inches x 300 pixels).

If you stretch the image to 8 x 10 inches, the pixels get bigger allowing only 150 of them to fit along an inch of space. Nevertheless there are still the same 1200 pixels on the 8-inch side and 1500 pixels on the 10-inch side– only the size of the print has changed making each pixel bigger and easier to see.

So the total number of pixels stays the same, regardless of the image size, but the number of pixels-per-inch (ppi) becomes less as the image size increases and vice-versa.

Here’s the bottom line: Small prints of the same photo will have more (and smaller) pixels to the inch ( and thus a higher ppi number); larger-sized prints of the same photo will have bigger pixels and less of them to the inch (a lower ppi count).

Generally speaking, you need more pixels-per-inch when printing large photos or you will begin to see the image begin to break down into individual pixels instead of appearing smooth. But you don’t necessarily need a camera with an ultra-high pixel count. A camera with as few as 6MP (or even less) will yield an image with enough pixels to output excellent 11×14-inch full-frame prints on your printer.

However, if you want to print very big images or frequently crop your images to blow up just part of them, you’ll need a higher resolution camera to give you an adequate number of pixels-per-inch so that individual pixels won’t begin to show and mess up your image.

Click to read Back to Basics: Resolution Simplified Part 2

In Part 2 we discuss printer resolution (measured in dots-per-inch), how to add more pixels if you need them and what the best settings are to use when you print.