Derivative maps vs. Tangent Space Normal maps I discovered that some engines use derivative maps instead of tangent space normal maps.

After some reading, it seems to be a really awesome way to replace tangent space normals but are there some disadvantage using them ? Why still continue using tangent space normals ?

Is it possible to compare both with advantage and disadvantage ?
After some researches and some answers from professionals here is my conclusion.

Pros


Don’t require tangents or binormals. Less interpolators.
Only need two channels. less texture memory.
Don’t suffer from tangent seams.
Can be blended using alpha blending, without renormalization.
Less mesh memory: We don’t need to store a tangent vector.
Fast implementation.


Cons


More ALU
Less flexible. A normal map can represent any derivative map, but the reverse is not true. As an example, sharp edges can be difficult to represent.


So, that's a lot of pros compared to cons. But the major problem is that it's not an industry standard.
There are almost no content authoring tools nor artist know-how.

Here's is a quote from Bart Wronski that illustrates well the current status of derivative maps :


  Sadly in life / technology not always best solution wins / not even
  gets deserved attention... It's more about standards and inertia.


If you are interested in knowing more about derivative maps here are some interesting articles.


Mikkelsen and 3D Graphics: Derivative Maps | Morten Mikkelsen Blog
Derivative Maps | CodeItNow
Derivative Maps vs Normal Maps | CodeItNow
Triplanar Texturing with Derivative Maps | The Robot Seven
Derivative Normal Maps - What are they? | polycount.com
Derivative Maps | Knald Technologies Documentation


If I forgot something or if your don't agree feel free to tell in the comments, I would be glad to improve this answer.