John Penczek

Consistency and Standardization of Color in Medical Imaging: a Consensus Report

This article summarizes the consensus reached at the Summit on Color in Medical Imaging held at the Food and Drug Administration (FDA) on May 8–9, 2013, co-sponsored by the FDA and ICC (International Color Consortium). The purpose of the meeting was to gather information on how color is currently handled by medical imaging systems to identify areas where there is a need for improvement, to define objective requirements, and to facilitate consensus development of best practices. Participants were asked to identify areas of concern and unmet needs. This summary documents the topics that were discussed at the meeting and recommendations that were made by the participants. Key areas identified where improvements in color would provide immediate tangible benefits were those of digital microscopy, telemedicine, medical photography (particularly ophthalmic and dental photography), and display calibration. Work in these and other related areas has been started within several professional groups, including the creation of the ICC Medical Imaging Working Group.

24.2: Robustness of Display Reflectance Measurements: Comparison between BRDF and Hemispherical Diffuse Reflectance

We measured in-plane bidirectional-reflectance-distribution-function (BRDF) profiles for specular, haze and Lambertian samples using a converging light beam and a photopic photodiode. The results were validated by comparing the hemispherical reflectance values calculated from BRDF data with direct measurements by the use of integrating spheres, whereby an agreement to within 2 % was achieved.

Evaluating the optical characteristics of stereoscopic immersive display systems

As large immersive displays have evolved over the years, the measurement methods used to characterize them must also advance to keep up with the changing technologies and topologies. We propose a general suite of optical measurements that can be used to determine the basic visual performance characteristics for a variety of immersive display systems. These methods utilize current display industry best practices and new research that anticipates the measurement challenges posed by the new technologies. We discuss the need for higher resolution detectors for the new generation of laser and LED (light-emitting diode) projector systems. The introduction of multi-primary displays is addressed by the implementation of new test patterns that better simulate the display performance of typical images. Methods to evaluate the unique attributes of stereoscopic displays, such as cross-talk and left eye/right eye differences, are described and interpreted. In addition, it is shown that the ambient lighting environment or display topology can have a detrimental impact on the display image quality. The application of these measurement methodologies is demonstrated by the evaluation of three display systems: two rear-projection and one front-projection display. We highlight how these measurements can identify potential display performance limitations, and offer advice on how to address some of these limitations.

Effect of local crosstalk on depth perception

Interocular crosstalk has a significant undesirable effect on the quality of 3D displays that utilize horizontal disparity. This study investigates observer sensitivity when judging the depth order of two horizontally aligned dots on a 3D display and assesses 3D display uniformity by obtaining this index for various locations on the display. Visual stimulus is two horizontally disparate dots, with nine steps of horizontal disparity. A dot pair is presented at five screen locations. An observer wearing polarized glasses sits 57 cm from a display, observes it through a slit, and judges the depth order of two dots. Each of the 20 observers responds 16 times per disparate dot pair, and we calculate the rate at which observers judge the dot on the right to be nearer in 16 trials for each display, screen location, and disparity. We then plot the rate as a function of the left–right dot disparity and fit a psychometric function to the plot. A curve slope at a response probability of 50% is used to gauge the sensitivity of depth order judgment. Results show the depth sensitivity variation across the display surface depends on interocular-crosstalk variation across the display thus its uniformity of the display.

24.1: Character Contrast under Uniform Ambient Conditions

The measurement of small-area black regions (such as a character stroke) on a white screen can be subject to large errors because of veiling glare in the detector. By using replica masks we can enable more accurate measurements of small-area-black and character contrasts even under ambient illumination.