Abstract
Abstract: :
Purpose: The effect of a novel wide–band image enhancement on the perception of TV images by patients with AMD was studied by measuring their preferred enhancement levels and their perceived quality of such individually enhanced images compared to the originals and to arbitrarily enhanced images. Methods: Visually relevant bar and edge features were located in the images using a dual–polarity edge detector based on a vision model (Peli, Proceedings of the IEEE, 2002:78–93). The contrast of the pixels of such features was enhanced, scaled according to the strength of the edge, and then added to the original image. Images (static) were randomly grabbed from cable TV channels and grouped into five major content categories. Patients selected their preferred enhancement level by moving a mouse over a graphics tablet. Ten images enhanced at 10 levels, the original, and 4 levels of image degradation were used. The median individual selection was used to enhance images for a second procedure. Patients compared the quality of 50 test images with individually–selected enhancement to that of the original images, the same images processed using an alternate arbitrary enhancement level, and degraded images. Data were analyzed using a signal detection approach. Results: Visually–impaired patients (n=35) could distinguish the wide–band enhanced images and preferred them over the original and degraded images. Most patients preferred a moderate level of wide–band enhancement. They reported preferring natural–looking images and thus rejected visible artifacts of the enhancement at higher levels. Preference was not correlated with visual acuity (r=0.07, p=0.75). Comparison of the enhanced images to the originals by 23 of the patients revealed that there was a slight preference for enhancement of multiple face images (Area under ROC= 0.60 ± 0.037) compared to other content categories. Improvement in the perceived image quality was high and statistically significant for only 22% of these patients. Discussion: A possible reason for the limited increase in perceived image quality is the rejection of distortions caused by the enhancement of pixel noise and the unnecessary enhancement of high contrast features. This might be solved by applying a low–pass filter to the original image before enhancement and by enhancing only moderate contrast features. Another possibility is that adaptation to image sharpening might occur. Leaving some part of the image unprocessed might counteract this effect.
Keywords: image processing • low vision • clinical (human) or epidemiologic studies: systems/equipment/techniques