Out of inDesign, the printed material looks too dark. I get the dot gain thing, but I need to know how much to increase brightness

For creating books with images that go off the page, export the file from inDersign as (from the “File > Adobe PDF Presets” menu) PDF/X-1a:2001.

Looking into finding cheaper services to print my Kinetik Festival photo books I came across CreateSpace. I think at this point of my self publishing