Why is the default Gabor phase offset 90 degrees?

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This is using the default (CV_PI*0.5,) phase offset getGaborKernel(size, 8.0, 0.0, 16.0, 1.0);

This is using a zero phase offset getGaborKernel(size, 8.0, 0.0, 16.0, 1.0, 0.0);

So it seems that default phase offset (90 deg) removes the symmetry of the Gabor kernel. I have seen some other references where they use the same offset so I guess its standard conversion.

Why is this the default? Is it generally more useful to have this for feature extraction?

Also asked on stack overflow.