The Constant MTF Interpolator a resampling technique with minimal MTF losses
Ellis Freedman, Robert Fleming · 2016
The geometric remapping of pixel values during the processing of digital imagery, such as magnification, warping and registration, can significantly affect the final image quality. Many medical imaging systems include a resampler/interpolator, such as bicubic, as part of their processing, that acts as a variable low pass filter. This not only degrades the spatial frequency response of the image and increases blurring, but varies the degradation with the fractional pixel interpolation distance. Thus the final modulation transfer function (MTF) of the image is often degraded in an almost random pattern for which accurate compensation cannot be applied. This reduces image interpretability and degrades pixel intensity accuracy. To counter this, a replacement table of interpolation kernels has been developed that imposes virtually the same MTF degradation for any pixel interpolation distance. The inverse MTF can then be applied such that there is minimal MTF degradation to the image after interpolation. This paper provides the latest results of analyses and simulations comparing the performance of the improved Constant MTF Interpolator (CMTF) to the cubic interpolator. These results indicate that the CMTF provides dramatically better image quality, preserves pixel intensity fidelity, and enhances the placement accuracy of pixels in the resampled imagery more than other tested interpolators.