Where Is The Image Going?
Knowing where you intend to use the images you create can help you determine what the resolution should be. If you’re planning to use the image on a website, there’s no point in using a high-resolution image, mostly because the file sizes tend to be enormous. But also because these documents are going to be viewed on a computer or a mobile device. The screen only displays 72 pixels per inch, no matter what resolution you set for the image, so there’s no point to using them. The user is never going to see more than 72 ppi, but it’s okay. They don’t need it. It’s only when the image is going to be printed onto a surface that you have to consider resolution.
Digital vs. Print
Because so much of what we see now is digital, you don’t have to think about resolution. But if the image is going to be printed on paper, it really matters. If the image is going to be used in a newspaper, 72 ppi is the standard resolution because the paper will only support low-resolution images. If the image is going to be printed with a laser printer, the maximum resolution is 300 ppi. Laser paper is thicker than newspaper and the toner (ink) is made for printing images on that kind of paper. So 300 ppi is fine if you know the images are only going to be used in a document that’s going to be printed on a laser printer.
But if the images are going to be used in a magazine, an annual report, or some other document that will be output (printed) on glossy paper, a high-resolution image will be required. These documents will need to be “separated” into cyan, magenta, yellow and black plates by a professional printer. So if you know the images are going to the printer for a process called “four-color separation”, your images must cram more pixels into every inch of space to get the sharp, vivid image quality you see in magazines.
For this reason, you plan your images by starting at the end of the process. Knowing exactly how and where you intend to use your images is important, because you will set your resolution accordingly before you begin.
NOTE: If you’re not sure how your image will be used, it’s best to start with the highest quality image you can make. Remember, pixels are little buckets full of numbers that tell the computer what color to make them, how transparent or opaque to make them, etc. It’s much easier to get rid of this mathematical information than it is to add it later. While there’s software out there that will allow you to enlarge your image, just remember that you’re trying to add information to the image that was never there, so the end result may not be as good as it might’ve been if you’d started with a high-res image. Such software is generally used when you have a low-res image that you didn’t create. You got it from somewhere and you need it to enlarge it, so that kind of software is helpful but the quality of the original is always an issue. Garbage in, garbage out. If it was a cruddy, low-res image to begin with, you can expect to improve the quality but don’t expect it to be perfect.