Today’s Question: When I am saving a TIFF image as a JPEG for a web display, is there any advantage to saving the image at 100 pixels [per inch] vs. 72. I made an assumption that by adding pixels, it would allow the viewer to ‘zoom’ in for greater detail.
Tim’s Quick Answer: The pixel-per-inch resolution for an image is irrelevant for an image shared digitally, such as on a website. All that matters are the overall pixel dimensions for the image, and that those dimensions represent enough pixels to display at the intended size.
More Detail: The pixel-per-inch (ppi) resolution value is only applicable when printing a photo, and even then is mostly just helpful for making sure you have enough pixels in the source image to print at optimal quality for the intended print size. For images shared digitally only the actual number of pixels matters, with the pixel-per-inch resolution being irrelevant.
Generally speaking, when sharing an image online you will only be presenting that image at specific pixel dimensions, and therefore the viewer would not be able to zoom in on the image to get a more detailed look. The viewer could certainly zoom with their web browser, for example, but that would only be enlarging the view of the image rather than revealing more pixels, and therefore the image quality would suffer.
In some cases it is possible to have a lower-resolution image, such in a blog post, that links to the full-resolution image. In this type of situation, it can be helpful to use moderately large pixel dimensions if you want the viewer to be able to get a detailed look at the full-resolution version of the image being shared.
Again, when sharing an image digitally all that matters are the pixel dimensions, not the pixel-per-inch resolution. You therefore want to balance the settings for those pixel dimensions in a way that balances your desire to share the image with good quality at a reasonable size with the desire to keep the image relatively small so it can’t be printed very large if the image is copied without your permission.