Why should you care about understanding DPI & Resolution? Because if you are going to print something (particularly of quality) or are ever tasked with optimizing images for the web, knowing a few basics will save you a lot of time and give you the best results.
Alternatively, if you ever hire someone to develop print materials for you or build you a website, they’ll likely have requirements you won’t understand and not everyone is good at explaining them.
Read on for a simple explanation of what you need to know.
It’s important to begin with a high-quality image which means the highest resolution and image dimensions you can get. When it comes to source images, bigger is better, because you can go down in size but not up without losing quality.
Definitions (in serious layman’s terms):
DPI: Dot’s per inch. The number of dots or pixels in a single inch. The more dot’s the higher the quality of the picture (more resolution, more sharpness and detail,… ).
Resolution: The easiest way I can explain resolution is to say that more resolution means an image displays more detail (or is capable of displaying more detail). Higher DPI means higher resolution. Resolution is not “size”, but it’s often confused with it because higher resolution images are often bigger, but that doesn’t necessarily have to be the case.
Print: 300dpi is standard, sometimes 150 is acceptable but never lower, you may go higher for some situations.
Web: 72dpi or 96dpi. Technically this “old mantra” is misleading, but we won’t get into that level of depth here. Accept it for now and let’s move on.
Let’s see it in action…
If you are sending someone images to use for print (again, that brochure you are having made) and they tell you the images are “too small” odds are the resolution wasn’t high enough. The image might look great and huge on your computer but is actually really small when printed out. To add to the confusion, your monitor resolution will also determine how big the picture appears to you when viewing it on your computer.
A monitor set to 800×600 will show an 800 pixel wide by 600 pixel tall image as a full screen image. On a monitor that is 1600×1200 the image will only take up 1/4 the screen. You might have thought it would take up half, but it’s actually going to be 1/2 as wide and 1/2 as tall (so 1/2 times 1/2 = 1/4). Long story short, the image will look much smaller on that screen even though the image is the same size.
Here are a couple of quick examples to show you the difference, no matter what your monitor resolution, it’s all relative!
The first example below has a lot of detail and is at 300dpi (even though the web is 72dpi this works for our purposes)
The second example is at 72dpi but scaled up to the same size so you can see the difference in detail. The actual image would be about 1/4 the size when you go from 300dpi to 72dpi, but at the same height and width is where you can actually see the difference.
Hopefully this has helped you get a little clearer on the differences between DPI, resolution and why if you have someone do something for you in print there will be different requirements than for the web. It’s also why that digital camera with higher megapixels takes better pictures than one with lower (lenses and other factors being equal), because it gives you more resolution to capture more detail.
Another important note about monitors, even though 72dpi is standard for the web, monitors have slightly different resolutions depending how you have the monitor set and how big the monitor is. For example, a 19″ monitor set to 1024×768 will show 70ppi (pixels per inch, monitors use pixels which are square not round but pixels and dots for the sake of this conversation are otherwise analogous). By comparison, a 19″ monitor set to 1280×1024 will have a resolution of 87ppx which means you fit more on the screen and get more detail, but everything looks smaller.
Side bar: image files with higher resolution (more dpi) will also have a bigger file size because they contain more data. Start with the biggest images you can but when putting images on the web they should be set to 72dpi, it’ll save you a ton of bandwidth and they’ll load faster. Yes, they’ll be smaller than the original but should in most cases be plenty big because of monitor resolution (ppi) sizes.
One last thing, don’t confuse “image size” with “file size.” Image size refers to the dimensions of the image while file size is how much space the image takes up on a hard drive (kilobytes or megabytes).
Any more questions on DPI, PPI, Resolution? Ask in the comments and we’ll try to clarify.