Weird lights, reflections and shadows on objects

You're right.


If you mean NormalMap Online, then move the sliders on top.


When you create a normal map from a diffuse map, you get a lot of extraneous/incorrect information. Black represents minimum height and white represents maximum height. So, for example, shadows or dirt get processed the same way as depth and highlights get processed the same way as height. It's a rather dirty way.

However, this method is used. But these normal maps need some fiddling and heightmaps are better for this purpose.

This old post explains it well, even though it's about Doom 3.

Also creating a normal map from a heightmap (or diffuse) is good for things like patterns, chipped edges, cracks, bolts, buttons, etc. Therefore, it's pointless for your picnic table, which doesn't have any surface information. You shouldn’t be approaching this like, "I should definitely make a bump map." Think about whether it will improve your model.

Free programs for generating normal maps from textures: xNormal (also has a plugin for Photoshop), Materialize, AwesomeBump, ShaderMap. And of course free GIMP and paid Photoshop.