In the practical sense, resolution is usually judged by imaging test targets bearing sets of spaced black-and-white lines in a square-wave pattern, and determining the minimum spacing for which the lines are distinguishable in the resultant image. With instrumentation readout, resolution target charts are less ambiguous and more useful if they bear sets of spaced “black” and “white” lines sinewave modulated in density, rather than square-wave modulated. Whereas square-wave targets introduce a Fourier series of higher frequencies, sinewave targets limit the analysis to a single frequency for each line set. Quantitative measurement of the modulations provides convenient determination of the transfer function.