The difference between a “high resolution” image and a “low resolution” image is huge.
First, let’s start with what those terms mean in the first place:
Print Quality – High Resolution
(A.K.A. 300 dpi or more). An image that contains 300 dots per inch (dpi) or more. If you take a magnifying glass and look at a printed picture, you can see dot patterns of colors that create the image. The higher the resolution (dots per inch = dpi), the harder the dots are to see because they are more concentrated (closer together) thus creating a very clear picture ideal for 4-color process printing. Printing a piece requires a 300 dpi resolution image, or it will appear grainy and poor in quality. These images can be used for printed materials or re-sized for web or digital use.
Web Quality – Low Resolution
(A.K.A less than 300 dpi). An image containing less than 300 dots per inch. If you take a magnifying glass to your image, you would see the actual dots of color more clearly because they are less concentrated (further apart). Internet browsers display images at low resolution 72 dpi. If images were used at high resolution, it would take minutes to download one image, rather than the few seconds it should take. These images should only be used for web or digital use.
Images that are high resolution can be converted to low resolution with software like Adobe Photoshop. But converting from low to high is not so simple. When an image is converted to low resolution, it loses quality and crispness. It’s referred to as “degradation.” When you try to take low to high, the software doesn’t know what is missing from the image to make it sharp and vibrant. So if you convert a high resolution image to low, be sure to keep the high resolution file, and save the lower one as different file name.
How do you know if a file is high or low resolution? There are a few different ways to tell if you don’t have photo imaging software, such as Photoshop. If you have a JPEG file, as an example, and it’s under 1mb in size, chances are it is low resolution. Anything above that, and it will likely be a high resolution (300 dpi).