interpolation comparisons between user code and copyresampled

ImageCopyResampled: 1.76
ImageCopyResampledBicubic2: 21.46
ImageCopyResampledBicubic: 31.84

imagecopyresampled (left), ImageCopyResampledBicubic (right), ImageCopyResampledBicubic2 (optimized) (bottom)