Abstract
PURPOSE: We wish to discover the visually-optimal method of displaying textual information on a patterned background display, such as might be used on an aircraft head-up display. METHOD: Three blocks of randomly selected words were rendered in a fixed color (green) over a chromatic noise background. Observers searched for one of two target words, and response time was measured. Four rendering algorithms were used, and all produced subjective impression of transparency. For each algorithm, the “strength” of the text component was varied. RESULTS: Response times varied from 4 to 20 seconds. Four predictors of text readability were used: text contrast, background contrast, and relative text contrast (text contrast divided by background contrast), all solely based on luminance, and pooled cone contrast of the text relative to the background. Spearman rank correlation was calculated between the predicted and observed response times. For all algorithms, response time decreased with increasing contrast, as expected. Of the four predictors, cone contrast (r=−0.61) was better correlated with response time than relative text contrast (r=−0.38), text contrast (r=−0.31) or background contrast (r=−0.32). CONCLUSION: Although we can not rule out the possibility that a model based solely on luminance contrast could explain the data, the fact that we obtain the highest rank correlation using pooled cone contrast suggests that chromatic factors may be significant. We plan to investigate whether a model of human perception of chromatic transparency may better explain the data.