Abstract: The human visual system's response to luminance discontinuities on continuous image gradients is measured. It is argued that since quantization artifacts often appear on smooth gradients, the versatility of sinewave gratings in controlling gradient properties can be used to quantify worst-case situations. The threshold spatial dimensions of discrete steps, such as would appear in a staircase approximation to the grating, are determined under a variety of experimental conditions. The smallest threshold step size defines a critical sample size, which is used to calculate limits for artifact-free reconstruction of sinusoidal luminance gratings. Rather than employ ad hoc collections of test images, the methods and results described suggest a more general approach to achieving visually optimal allocation of imaging resources. !3
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