Today’s Question: Sometimes when I have worked in the Book Module [in Lightroom Classic CC] I get a message just before I send my work to Blurb. It says “Some photos in the book have transparency. The transparent area will show as opaque in your book”. When I go to each photo referenced, I cannot see anything that renders the photos defective and I am not even sure I know what transparency even means. Can you help me understand this issue and is it something I should be concerned with?
Tim’s Quick Answer: You can think of “transparency” in this context as areas of a photo that don’t have any pixels, or that has pixels that are hidden. Because Lightroom does not support transparency, that will translate to areas of the image that are white, which generally would not be a problem. In other words, in most cases you can simply ignore this message, though you can test the output first with a PDF document.
More Detail: While Lightroom does not support image transparency directly, it does support image formats that can contain transparency. A common use of transparency is to place a graphic against a background. For example, you might have a round logo you want to place against a textured background. Instead of having that round logo appear on top of a white rectangle, which in turn is placed on the textured background, transparency enables you to avoid the visible white rectangle.
You can create transparency in Photoshop in a variety of ways, such as through the use of a layer mask. In this case, I suspect you have some layered TIFF images in Lightroom that contain some degree of transparency that doesn’t actually result in any area that doesn’t include pixels. Lightroom can’t tell, however, whether the transparency might create a problem for your book, to the alert is given anytime an image included in a book project includes transparency.
You can test the result by first creating a PDF document for your book. At the bottom of the left panel in the Book module you can click the “Export Book to PDF” in order to render a PDF version of your book. You can then review that document to make sure the images with transparency appear correctly. For example, you would want to make sure that an image was not cropped to create edges that are not at right angles, because that could result in a warped appearance on the printed page.
If the PDF looks good, you can ignore the error and proceed with production of your book. If you want to avoid the error altogether, you could create your book with JPEG (or flattened) copies of your images. But again, in most cases the error is not an issue and can be ignored after you’ve reviewed a PDF copy of the book.