<title>Perceptually standardized imaging of digitized film for comparative ROC measurements</title>

Abstract

Primary diagnostic reading of digitized film, displayed on a CRT, requires a quality assurance (QA) that all of the perceptual information, which is accessible from the film when displayed on a light table, can be reproduced on the CRT display. Some of the CRT display parameters are already defined. The DICOM standard 3.14 introduces a contrast transfer function (grayscale display function standard) for minimum contrasts which are defined as single just-noticeable- differences (JND) in luminance. It establishes, throughout the entire intensity range of the data, contrast recognition of single JND resolution and implies linearity of contrast perception. Conventionally, the CRT QA utilizes a SMPTE contrast test pattern of 5% contrast ]13 digital driving levels (DDLs)[ resolution. We developed for the QA of the new standard a perceptual contrast pattern with single DDL resolution (perceptual contrast pattern equals P-pattern). It allows the visual assessment and measurement of perceived contrast linearity at a minimum level 1.2% contrast (3 DDLs). We analyzed, at various room light conditions (0 - 300 cdm<SUP>-2</SUP>) and on DICOM 3.14-standardized CRTs of various maximum luminance (110 - 400 cdm<SUP>-2</SUP>), the minimum luminance of the CRT that is required for establishing perceptual contrast linearity. We compared the use of the SMPTE pattern and the P-pattern for QA of linearity. The SMPTE pattern was not effective for a statistically significant correlation of contrast linearity with room light and monitor luminance. However, the P-pattern furnished an effective tool for the assessment, measurement or adjustment of contrast linearity. We found that perception of linearity for 3 JND contrasts at low room light conditions (0 - 6 cdm<SUP>-2</SUP>) requires a minimum luminance of 10 cdm<SUP>-2</SUP> which is not directly derived from the background luminance of the light reflected from the monitor but may indicate a perceptual threshold value for task performance.