Kingdom F, Moulden B, 1986, "Digitized images: what type of grey scale should one use?" Perception 15(1) 17 – 25
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Digitized images: what type of grey scale should one use?
Fred Kingdom, Bernard Moulden
Received 9 October 1985, in revised form 22 January 1986
Abstract. One of the issues faced by engineers when designing a system which records an external event and represents it in the form of a digitized image on a VDU screen is which type of grey scale to use. An experiment is described which compares, in a simulated digitized image, the effect of a linear and a logarithmic grey scale on the detectability of a straight-line signal embedded in visual noise. It was found that both bright and dark signals were detected more easily with the linear scale. A signal detection theory analysis was carried out to compare human performance with that of an 'ideal' observer who performed the detection task with a filter spatially matched to the signal. It was found that the model of performance for this ideal observer accounted well for the results provided the assumption of a linear transformation of luminance was made. The analysis showed that the superiority of the linear over the logarithmic grey scale was simply due to the higher signal-to-noise ratio of the signals in the former.
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