normal maps vs. the programmer

Wookie Smack

A couple of months back zbrush generated a wierd, very green normal map. at the time i had never used zbrush so didnt know what to expext. since then i have never seen anything like it. today my programmer told me that was the correct normal map for direct x and that the blueish one that both photoshop, and 3d studio max generate(that happens to be the only kind i ever see anywhere) are incorrect for the purposes of direct x in games. is my programmer crazy or is it possible that max and photoshop do not produce normal maps "correctly"? are there different kinds of normal maps?

EarthQuake

There are a few different kinds of normals maps, however i've fairly certain what you got from zbrush was actually an object space normals map, since they tend to have more of a green-yellowish color. Whereas blue is tangents space. I'm not 100% sure but i think max can generate either.

If he is telling you tangent space is incorrect for games he is VERY wrong. Tangent space is the only type of normals mapping that can be applied to deforming meshes iirc.

Slum

Weird. The standard 'bluish' tint comes from the fact that for normal maps, the neutral values for RGB (X, Y, Z coords) is 128,128,255. The only thing I can think of is that some engines might use the blue values inverse, (i.e. the neutral value would be 0 instead of 255).

Thats just a guess though, I don't really know much about this kind of stuff.

EDIT: Didn't see EQ's post. Chances are he's correct, and I'm an idiot.

Jay Evans

hey earthquake, All the BF games I have worked on use world space normal maps on the characters. So it is dependent on the engine. For BF2\2142 stuff they are created as tangent space then converted to world when imported into the engine.

There is probably other engines that are similar.

EarthQuake

I must be thinking object space that can't be used on deforming meshes in that case? Or maybe someone has figured out a way around the problem that i didn't know about....

Eric Chadwick

Everything I've heard has explained that neither object- nor world-space maps can be used on deforming characters. Apparently you can use world-space maps on objects that rotate (which are then termed "object-space" maps tho they're the same pixel data as world-) but that's about it.

Jay, I'd love to see an example of a BF2 world-space character map, if you have one lying around. I'm with EQ tho, might just be some fancy tech thingy.

CrazyButcher

http://www.zen-x.net/images/GDC_2002_InGameSpecialEffects.zip

old paper from a guy, also shows how world-space normalmaps can be used on deformable characters (basically you just need to rotate the light vector a bit different than in tangent if I remember well)

Jay Evans

I can't post it here, but if you have BF2 go to:
C:\Program Files\EA GAMES\Battlefield 2\mods\bf2
then go into the archive Objects_client.zip, navigate to \soldiers\Us\Textures and poke around. Anythign "_os" is object space.

**oh.. and just a disclamer that messing with archived files in the BF install may mess up you're ability to play online. You may want to make a copy of it first.***

Rick Stirling

Your coder friend is correct. The compression you get with DXT is nasty nasty nasty to normal maps, so a trick is to move the red X channel into the alpha, since the alpha layer gets compressed separately.

This gives you a good tradeoff with compression and detail, and makes the normal map look green instead of purple.

Rick Stirling

Oh, and the reason red is moved and not green or blue is simple. Blue is the least useful colour in the normal map, so we move either green or red. But DXT compression of the 16bits favours green - it uses 5 bits to store red, 5 bits to store blue and 6 bits to store green.

So, we shift the red into the alpha channel and it gets a whole 16bits all to itself.

It's worth noting that you could theoretically store another map in the old red channel - like a simple spec map or a gloss map.

Eric Chadwick

Ahhh, I forgot about compression since we don't support it yet.

I seem to recall something about having to duplicate the green channel into all three RGB channels, because the Nvidia compressor figures in the differences between all three when it compresses each one. So if they're the same exact data, you get less artifacts. Alpha is apparently compressed totally separate.

Good one Rick.

Rick Stirling

I dunno how it's done - our exporter handles that from the TGA files.

Rick Stirling

Full version of my answer here, with extra details

http://www.rsart.co.uk/2006/08/27/green-tangent-space-normal-maps-2/

Mister Sentient

[ QUOTE ]
Full version of my answer here, with extra details

http://www.rsart.co.uk/2006/08/27/green-tangent-space-normal-maps-2/

[/ QUOTE ]

"So, we move the red data into the alpha channel and it gets a whole 16bits all to itself, leaving the green with 6 bits and blue with 5 bits."

I think that 16 should be a 6. Yes I am a stickler.

EDIT: I could be wrong of course.

Rick Stirling

You are wrong. It might be 8, but it's either 16 or 8.

Mister Sentient

[ QUOTE ]
You are wrong. It might be 8, but it's either 16 or 8.

[/ QUOTE ]

I apologise. I am indeed wrong.

Rick Stirling

But how wrong? If it's 8, you are only 2 wrong, and I'm 8 wrong which means I'm more wrong

Rick Stirling

It looks like it's 8bit.

Mister Sentient

That'll teach me to meddle outside my area of expertise.

Rick Stirling

and teach me to proclaim wrongness as good