Today’s Question: You addressed the resolution that should be used when resizing a photo for print using the Crop tool. But what resolution should I be using when I’m going to share a photo online or with a digital presentation?
Tim’s Quick Answer: When sharing a photo digitally (rather than printing), the pixel per inch (ppi) resolution is irrelevant. The actual pixel dimensions will determine how large the image is presented through digital means.
More Detail: The topic of pixel per inch (ppi) resolution is one that has long been confusing for many photographers. I think part of the reason this was originally an issue is that many people were under the false impression that Macintosh computers used a display resolution of 72 ppi and Windows computers used a display resolution of 96 ppi.
Today’s displays generally have considerably higher resolutions than the numbers noted above, and there is considerable variability depending on the size of the display and the resolution setting for that display.
The pixel per inch setting for an image doesn’t matter for digital sharing of photos. The pixel dimensions will determine how large the image appears with the specific digital output method you’re using.
For example, if you had a photo sized to about 960 pixels wide will take up half the width of a display that has a resolution of 1920×1080 pixels, assuming the image is presented at 100% scale. The ppi resolution set in the metadata for the image would not impact how it is presented.
Having said that, there are some applications that look at the ppi resolution setting for an image even though there is no need to do so. This would affect how large an image is sized when you place it into a document, such as for a slideshow presentation.
So, in general you can leave the ppi resolution setting to any value you’d like for images that will be shared digitally. If you feel better entering a specific value for the resolution field, a setting of 100 ppi will be reasonably close to the typical value for most digital output. But again, for most digital sharing scenarios, that information will be completely ignored.