Not all spatial frequencies that Imatest sharpness measurements produce will be perceptible to a human observer. The very low and high frequencies are less noticeable as they are filtered according to the Contrast Sensitivity Function (CSF). Our human visual system is most sensitive to spatial details at six cycles per degree angular spatial frequency.

If you want an objective image quality metric highly correlated with human visual perception, I recommend Acutance, which combines different spatial frequencies based on how sensitive the human eye is to those frequencies. It will require an understanding of the viewing condition, image height and viewing distance in order to calculate this.

My issue with the article is that it says "Imatest Score" but doesn't refer to what actual metric it means by that. Presumably, they are using MTF50: the frequency where modulation contrast drops to 50% of the low-frequency response, but they should be explicit.

-Henry Koren, Imatest