I am able to bake objects with one material, but when there is more than one, an error comes up:
No active image found in material "blah-blah". Most materials are used on many different objects, so I made each one a single user copy (clicking the number beside the material name field in Properties > Materials and renaming it descriptively). That didn't resolve it though.
I have been following the steps in this Blender Guru video (which explains how to bake the lighting onto an object's surface so it takes much less rendering to display it in an app like Sketchfab, or so you can work on it displayed in Render mode in real time):
UV unwrap > create and name image > add Image Texture > link to the image just created > make sure that node is selected > Bake. Since in this case the objects had several materials, I added an Image Texture to each one, linked it, and left it selected.
Do the UV maps need to be divided up so they only are for one material each? Does that mean I have to divide up the objects into a group of objects each of one material? What is the best way to do this?
(Oops, the file doesn't have the object selected that I was working on when this cropped up - it is the green floors inside the structure, named Dugout Levels.)