A validated subjective rating of display quality: the Maryland Visual Comfort Scale

Abstract

Background: Minimally invasive surgery requires high-quality imaging to provide effective visual displays to surgeons. Whereas objective measures--pixels, resolution, display size, contrast ratio--are used to compare imaging systems, there are no tools for assessing the perceptual impact of these physical measures. We developed the "Maryland Visual Comfort Scale" (MVCS) to measure perceptual qualities in relation to an imaging system. We theorize that what the surgeon perceives as a high-quality image can be summarized by a scoring of seven characteristics related to human perception, and that image quality is not homogenous across a video display such that object location impacts perception and display quality.

Method: We created a rating scale for seven dimensions of display characteristics (contrast, detail, brightness, lighting uniformity, focus uniformity, color, sharpness). For validation, 30 participants viewed test patterns and manipulated physiologic images, rating the image quality for all seven dimensions as well as giving an overall rating. Image ratings for contrast and detail dimensions were assessed across five locations on the video display. For ratings, two imaging systems were used, differing primarily in the 10-mm zero-degree scope's quality: a standard scope and one taken from service for quality degradation.

Results: The rating scale was sensitive to differences in scope quality for all seven items in the MVCS (all p values<0.01). Significant differences existed between quality ratings at central and peripheral locations (p<0.05).

Conclusions: This seven-item rating scale for assessing visual comfort is reliable and sensitive to scope quality differences. The scale is sensitive to degradation of image quality at video display edges. These seven dimensions of display characteristics can be refined to create a psychometric to serve as a composite of perceptual quality in laparoscopy.