Lots of times, we get sent images that are too small, or “lo-res” (short for low-resolution) to use for print. Here’s a helpful guide to understand the difference between using lo-res and hi-res images.
The first step to knowing the difference between high-resolution and low-resolution images is to understand what DPI means. DPI stands for ‘dots per inch’ which is a measure of the individual dots that can be placed in a line within the span of one inch. When viewing an image on your monitor, the dots are referring to “pixels”, or “picture elements”, which are the smallest visual elements (tiny little rectangles) on a display screen. When viewing a printed image, the dots refer to the actual dots of ink on the page. The more dots per inch, the higher-resolution the image. Think of it this way; what would make a clearer image? Ten dots of color per inch or 100 dots per inch?
Low-resolution → high-resolution
So, when does an image become high-res?
300 is the magic number! Anything under 300dpi is considered low-res and anything 300dpi or above is considered high-res. 72dpi is the standard for low-res.
Keep in mind…
When you have a seemingly large image (dimension-wise) that is lower-res, the dimensions decrease greatly when bumping up the resolution. For example: If I have an image that is 10×10” at 72dpi and I resize it to 300dpi, the dimensions decrease to 2.4×2.4”.
Why shouldn’t I just use high-res images all the time?
High-res images are great and designers love them. They’re clear, sharp, beautiful files and when you are printing anything it should always be high-resolution. But believe it or not, there are some reasons to use low-res images.
The standard resolution for internet browsers is 72dpi, so anything you see online is automatically low-res.
Smaller file size
It makes sense that low-res images are smaller file sizes than high-res images; they have so much less digital information. This means they take up less space, load much quicker, and are easier to send through email.
How do I tell the difference?
If you know how to use Photoshop you can check out an image’s size under Image>Image Size. Otherwise, generally, the larger a file size is, the higher-resolution it will be.
What’s the deal with vector art?
Vector based files are information based, rather than pixel based. They use points, lines, curves and shapes that are based on mathematical equations to produce images. Because they are not made up from pixels, the dots per inch measurement is not applicable for vector files and they can be scaled up to any size without losing quality. Vector files are typically used for line art such as logos, digital illustration and typography, whereas photography is always pixel based.
When in doubt, always send your designer the high-res image.
These can always be cropped down to the correct dimensions and dpi, whereas a low-res image’s resolution cannot be increased any higher than it currently is — once an image size is decreased, that digital information is lost. You cannot create a high-res file from a low-res file.