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Ming Mei, Susan Leat; Objective assessment of improved visibility with digital image enhancement for the visually impaired. Journal of Vision 2007;7(9):1045. doi: 10.1167/7.9.1045.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Observers with visual impairment show subjective preferences for pictures that are digitally enhanced with generic filters and specially-designed filters. The purpose of this study was to use a measure of performance to demonstrate improved visibility of images that have been enhanced.
Methods: Nine subjects with maculopathy were recruited. The range of digital filters included generic filters (high pass or un-sharp mask, contrast enhancement, Sobel edge enhancement, DoG convolution), and custom-devised filters (Peli contrast enhancement and filters based on contrast sensitivity and supra-threshold contrast matching results). The filters were applied to two groups of images (14 faces and 14 general scenes). Using subjective comparisons and ratings of perceived visibility of filtered images compared to unfiltered images, the best two filters were obtained for each subject. These two best filters were applied to another two groups of images (32 faces with four facial expressions and 7 general scenes). For the face images, subjects were required to recognize facial expressions (anger, disgust, fear, or sadness). Eight questions were generated for each general scene image. Percent correct was calculated for both sets of images comparing filtered and unfiltered images.
Results: Image enhancement improved performance both with facial expression recognition (paired t-test, p = 0.004) and questions about general scenes (6 or 7 out of 9 subjects show significant improvement - paired t-test, p[[lt]]0.05).
Conclusion: This study demonstrates that it is possible to measure improvements in visibility with digital image enhancement and that digital enhancement with a variety of generic and custom-devised filters improves visibility measured both subjectively and objectively for people with maculopathy.
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