17 June 2003 Contrast measures for predicting text readability
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Our previous experiments with additive and multiplicative transparent text on textured backgrounds show that readability can be more accurately predicted by adjusting the contrast with a contrast-gain-like divisive factor that includes the background RMS contrast. However, the factor performed poorly at predicting readability differences on two different patterned backgrounds. Using the same images of the previous study we presented the target words alone and single letters cut out of the target words. We found that word identification and word discriminability was affected by the backgrounds in the same way that the paragraph search performance was affected, but that letter identifiability on these two backgrounds was predicted by the metric. We also found a significant improvement from including different contrast gains for positive and negative contrasts in the metric. Unfortunately, word readability is not necessarily simply related to letter identifiability and simple contrast measures.
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Lauren F. V. Scharff, Albert J. Ahumada, "Contrast measures for predicting text readability", Proc. SPIE 5007, Human Vision and Electronic Imaging VIII, (17 June 2003); doi: 10.1117/12.479663; https://doi.org/10.1117/12.479663

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