1. An imaging system comprising a computer programmed to: perform an air calibration step on computed tomography (CT) imaging data, wherein the CT imaging data comprises projection measurement data; estimate noise in the projection measurement data; correlate the noise estimation with neighboring projection measurement data to generate a weighting estimation based on the correlation; de-noise the projection measurement data based on the noise estimation and on the weighting; calculate a negative logarithm of the projection measurement data; apply a mean preservation to the projection measurement data after calculating the negative logarithm; and reconstruct an image using the de-noised projection measurement data.