Bone rotation behaves differently to object rotation I have a problem understanding the rotation of bones. While objects are rotated around their axis as expected bones seem to behave differently (Even when the objects are parented).

In the first picture you see the sample object once with bones and once with separate objects. You can also see that the rotation angles are different while the result is (more or less) the same. However for the first bone and the respective object the rotation angles are both 0.


This picture shows the rest pose.



For my export script I want the rotations of the bone to be like the object rotations. I use quaternions but for understanding the problem better I displayed euler angles in the pictures.

Thanks in advance!
There are a few issues here:


The orientation of the bone at rest is not the same as the object. By default, the Y axis on each bone is along the main axis of the bone (i.e. the direction the bone is pointing). As blender uses Z-up as its standard coordinates, this most likely corresponds to the z axis on your object. 
Your object pivot point (the orangey dot when it is selected) does not match the pivot for the bone. This may, but not necessarily, cause differences in the rotations.
Euler rotations are not path independent, and as a result there are multiple ways to end up in the same orientation. Euler rotations are essentially a number of ordered rotations required to reach a given orientation, but there may be multiple ways to reach the same orientation. In this case try copying the values from the object to the bone and see which results you get.