Performance comparison of rectangular (four-point) and diagonal (two-point) dither in undersampled infrared focal plane array imagers

Undersampled staring array imagers exhibit sampling artifacts. Dither is a mechanical means of raising the spatial sampling rate without increasing the number of detectors on the focal plane array. Diagonal (two-point or slant-path) dither is easier to implement than rectangular (four-point or bowtie) dither. Also, diagonal dither generates half the data rate of rectangular dither. However, diagonal dither does not sample the image as effectively as rectangular dither. The cost and complexity advantages of diagonal dither must be traded against the expectation of reduced performance. We discuss analytical and empirical predictions of the performance difference between diagonal and rectangular dither. To compare diagonal and rectangular dither empirically, a target identification (ID) experiment was performed. The visual task involved target ID among a set of 12 tactical vehicles. High-resolution (close-up) images of the targets were blurred and downsampled to produce images representative of those seen with a 320 x 240 pixel staring array sensor. The nondithered imagery was poorly sampled, and the imagery with rectangular dither was adequately sampled. The experiment compared the static target ID performance of nondithered, diagonally dithered, and rectangularly dithered sensors. Analytical and empirical results are described.