When you click in a photo in the Book Module, a Zoom slider appears, which shows you how far, in percent, you are zoomed in on the photo, and allows you to zoom in more or less. This slider is for enlarging the photo in the cell on your Book page, not for zooming in to evaluate detail in the photo. (The latter is done with the Preview panel.)
If you zoom in too far, you’ll get an exclamation point in the top right corner:
If you click on one of these exclamation points, you’ll get this warning, indicating that you have enlarged the photo too much and may not have enough pixels per inch (ppi) to get a good quality print:
Note that this warning and ppi information will only display if in the Book Settings panel you have chosen to make a Blurb book, not for PDFs or JPEGs. In addition, of course, it only displays once you get down to under 200 ppi.
So how do you get Lightroom to display ppi for PDF’s, JPEGs, and for your Blurb book photos over 200 ppi? Here’s the secret:
- Click in the photo, so that the zoom slider appears.
- Hold down the Alt/Opt key — this changes zoom % to ppi!