Understanding the effects of Gabor kernel parameters

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In OpenCV you can create a Gabor kernel and specify some parameters such as; sigma, theta, lambda, gamma, phase offset.

I'm trying to understand the effects of these parameters. Apart from theta (the angle of the edge/texture I want to detect) I don't quite understand what they do or when I would want to use a large gamma vs a small gamma.

Is someone able to simply explain the effect of each parameter? For example "If you use a large sigma the results will be X", "If you want to detect weak 90 degree edges you should use PARAM_X with a value of Y".