对于像我这样喜欢快速参考的人来说，滤镜是
FILTER_UNDEFINED => UndefinedFilter
FILTER_POINT => PointFilter
FILTER_BOX => BoxFilter
FILTER_TRIANGLE => TriangleFilter
FILTER_HERMITE => HermiteFilter
FILTER_HANNING => HanningFilter
FILTER_HAMMING => HammingFilter
FILTER_BLACKMAN => BlackmanFilter
FILTER_GAUSSIAN => GaussianFilter
FILTER_QUADRATIC => QuadraticFilter
FILTER_CUBIC => CubicFilter
FILTER_CATROM => CatromFilter
FILTER_MITCHELL => MitchellFilter
FILTER_LANCZOS => LanczosFilter
FILTER_BESSEL => BesselFilter
FILTER_SINC => SincFilter
参考：https://github.com/vitoc/gmagick/blob/master/gmagick_helpers.c