Why should you care about understanding DPI & Resolution?
Because if you are going to print something 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.
On the other hand, if you ever hire someone to develop print materials or build a website for you, they’ll have requirements you may not 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.
I use several online sources for free and paid images and take a lot of my own pictures. If you are looking to improve your own pictures take a look at Photo Nuts & Bolts.
Definitions (in layman’s terms):
DPI: Dot’s per inch. The number of dots in a printed inch. The more dot’s the higher the quality of the print (more sharpness and detail).
PPI: Pixels per inch. Most commonly used to describe the pixel density of a screen (computer monitor, smart phone, etc…) but can also refer to the pixel density of a digital image.
Resolution: Resolution is the measure of pixels in the display, usually expressed in measurements of width x height. For example a monitor that is 1920 x 1080 is 1920 pixels across and 1080 pixels down.
Higher resolution means 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/Digital: DPI doesn’t equate to digital it’s a print measure. It was commonly believed for a long that 72dpi was ideal for web. If you hear that it’s simply not the way things work. When talking digital, we’re concerned with the actual resolution. How that image prints is another matter.
If you are creating images to use for print and the images are “too small” the odds are the resolution wasn’t high enough. The image might look huge on your computer but still print out quite small. To add to the confusion, your screen resolution will also determine how big the picture appears to you when viewing it on your computer.
A monitor set to 1024 x 768 will show an 1024 pixel wide by 800 pixel tall image as a full screen image. On a monitor that is 1920x 1080 the image will only take part of the screen. Long story short, the image will look much smaller on that screen even though the image is the same size because the screen has higher resolution.
Hopefully this has helped you get a little clearer on the differences between DPI, PPI, 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).