How do I make correctly a normal map from highpoly model for lowpoly?

Question

I have highpoly model (without textures and materials):

I want to move details from highpoly to lowpoly using NORMAL MAP

As I understood it is necessary: I did baking normal map for lowpoly FROM lowpoly model (it is not true, I want bake normal map from highpoly frog)

For baking lowpoly model I do next actions:

1. Create material for lowpoly and create these nodes (I have tiled UV unwrapping and created 4 uv maps previously):

next, I chose node with neccessery image and chose corresponding uv map, then I pressed "BAKE".

BUT how I can do the same with highpoly model to bake normal map for example. If I choose highpoly model I cannot choose UV unwrapping of lowpoly model. (Of course I can't create UV for highpoly model with millions polygons)

Answer 1

You use "selected to active" in bake settings to bake from one object to another. "Selected" is any number of selected objects that are not actively selected. "Active" is the actively selected object. So, for your example, select the high poly in 3D viewport, then shift select the low poly in 3D viewport. After that, your selected is the high poly; your active selection is the low poly.

There is no need to unwrap the high poly to bake. (There are techniques you can use that involve unwrapping the high poly; don't worry about that until you get the basics.) You specify the UV map only for the low poly (the actively selected), and you don't use nodes to specify it; you specify it by selecting that UV map in properties/object data/uv. Specifying the UV map in nodes does nothing. (This is a pretty common misconception, and maybe it's worth adjusting Blender's UI to match the misconception rather than trying to dispel it all the time.)

What determines what image you bake to is an actively selected image texture node. You do not bake all of the things you have at once; you have to bake them individually, marking them by selecting them and then baking (with appropriate bake settings), then saving the image; then selecting something new, changing bake settings, baking, saving the image; repeat until done.

(I'm assuming that you're not trying to bake 4 different normal maps, which wouldn't make any sense. I'm assuming you're baking diffuse color, normal, roughness, etc.)

A common thing that throws people is that what makes something the active selection is backwards when selecting via the outliner. The active selection has a more yellow outline; the rest of the selection has a more red outline.