Request for Comment: Bump Maps or Normal Maps?

[SevenSpheres]

I'm working on updating Celestia's default data again, after about a year with not much being done in this area. (If you have mobile Celestia, you should be able to see new content shortly after it gets added to the repository.) One thing I need community input on is what kind of map should be used to display elevation: bump maps or normal maps. In either case, one type of elevation map should be consistently used.

Bump maps are used by Celestia 1.6.x, while normal maps are used by Project Echoes. Normal maps are IIRC what Celestia uses internally (bump maps are converted into normal maps before being rendered) and so are probably more efficient; but they're less "human-readable", harder to create, and they have to be png images, which are larger than jpg images and thus increase Celestia's file size.

[john71]

Normal maps are better. I use DXT5nm files and they are way better, than bumpmap files. Also Gimp can create normal maps from any image.

[SevenSpheres]

Also Gimp can create normal maps from any image.

I'm pretty sure that it can't properly convert bump maps into normal maps; it just assumes that the input image is not already a height map and guesses the elevation of it. There's Fridger's normal map tools, but I don't know if they're still available.

Edit: A look through the Discord server history finds this GIMP normal map plugin. I'll try it out. Edit2: I'm not sure that this is any better...

Actually it looks like I may be wrong here and the default normal map filter can convert bump maps.

Okay, it turns out the problem is just that it doesn't work exactly as it should for a texture mapped to a sphere (the scale at the poles is wrong). Other than that it does correctly create normal maps from bump maps. Sorry for the confusion.

[john71]

I never used Fridger's tools, only Gimp. Normal maps are not scientific, but mainly aesthetic tools in my opinion. They have this very crisp, clean visual effect. Bump maps are lame and somehow foggy. In any case Celestia should provide a command to use DXT5nm files, because they are in almost every way superior to jpg files or bump maps.

[SevenSpheres]

Normal maps are not scientific, but mainly aesthetic tools in my opinion.

Normal maps (at least the ones that would be used in the default Celestia distribution) are scientific; they encode real planetary elevation data. See Digital elevation model.

[john71]

they encode real planetary elevation data

The main problem is that in many cases you cannot see this elevation data in real life (from space), but normal maps can make or break a planet or a spaceship in Celestia. They add a special sense of reality.

Added after 14 minutes 34 seconds:

A look through the Discord server history finds this GIMP normal map plugin. I'll try it out. Edit2: I'm not sure that this is any better...

Gimp 2.10 Filters->Generic->Normal map

[John Van Vliet]

I use all Normal maps and and a copy of Fridger's tools so that the poles are correctly mapped

Gimp DOSE NOT DO THIS!!!!!!

Normal maps just work better than a 8 bit height map

[trappistplanets]

Normal maps just work better than a 8 bit height map

yeah, i agree, it reduces color banding artifacts (see https://en.wikipedia.org/wiki/Colour_banding)