One of the elusive things that film and images from high-end cameras have is often called "thickness".  I suspect that people who talk about "density" are also talking about the same thing.  It's the opposite of the images that come from low quality cameras, which are often described as "thin" "brittle" and "digital". Please help me figure out what it is, so perhaps we can 'cheat' a bit of it in post. My question is - what aspect of the image shows thickness/thinness the most?