Wei-Chung Cheng

Assessing color reproducibility of whole-slide imaging scanners

A new method for assessing color reproducibility of whole-slide imaging (WSI) systems is introduced. A color phantom is used to evaluate the difference between the input to and the output from a WSI system. The method consists of four components: (a) producing the color phantom, (b) establishing the truth of the color phantom, (c) retrieving the digital display data from the WSI system, and (d) calculating the color difference. The method was applied to a WSI system and used to evaluate the color characteristics with and without color management.

70.2: Virtual Display: A Platform for Evaluating Display Color Calibration Kits

We propose a method of evaluating the performance of color calibration kits for LCD monitors. Routine color calibration is imperative for critical applications that rely on color fidelity such as digital pathology and professional graphics. However, the commercially available products vary greatly in price and performance with no available evaluation standard. We propose the concept of Virtual Display, a universal display platform that emulates tone reproduction curves. A field programmable gate array board was used to process the video signals based on a preprogrammed look-up table, which contains the tone reproduction curves of the target display. A spectroradiometer-based and a colorimeter-based color calibration kits were challenged by 8 virtual displays that have problematic tone reproduction curves. The results show that both color calibration kits offer only one-dimensional lookup tables for each channel, which might be insufficient. We also spectrally characterized three real displays of different grades and derived spectral models for them. By using the virtual display and spectral models, evaluation of color calibration kits can be greatly simplified and standardized without the burden of optical measurement on target displays.

A Gaze-contingent High-dynamic Range Display for Medical Imaging Applications

The grayscale resolution of current liquid crystal display technology limits its applications in medical imaging with wide dynamic range and dense grayscales are required. We propose an approach that dynamically processes the display image such that the luminance and contrast of the gazed area is optimized. A gazecontingent interactive display system based on an 8-bit LCD and an eye-tracker was implemented to emulate the proposed concept for a high-dynamic range display.

Towards standardized assessment of endoscope optical performance: geometric distortion

Technological advances in endoscopes, such as capsule, ultrathin and disposable devices, promise significant improvements in safety, clinical effectiveness and patient acceptance. Unfortunately, the industry lacks test methods for preclinical evaluation of key optical performance characteristics (OPCs) of endoscopic devices that are quantitative, objective and well-validated. As a result, it is difficult for researchers and developers to compare image quality and evaluate equivalence to, or improvement upon, prior technologies. While endoscope OPCs include resolution, field of view, and depth of field, among others, our focus in this paper is geometric image distortion. We reviewed specific test methods for distortion and then developed an objective, quantitative test method based on well-defined experimental and data processing steps to evaluate radial distortion in the full field of view of an endoscopic imaging system. Our measurements and analyses showed that a second-degree polynomial equation could well describe the radial distortion curve of a traditional endoscope. The distortion evaluation method was effective for correcting the image and can be used to explain other widely accepted evaluation methods such as picture height distortion. Development of consensus standards based on promising test methods for image quality assessment, such as the method studied here, will facilitate clinical implementation of innovative endoscopic devices.

Evaluating color calibration kits with virtual display

ABSTRACT Routine color calibration is imperative for medical applica tions that rely on color fidelity such as digital pathology, endoscopy, and colposcopy. However, commercially available products vary greatly in price and performance with no available evaluation standard. Related studies have used only one or a few displays to evaluate the performance of color calibration kits. We propose the concept of Virtual Display, a universal display platform that emulates the colorimetric response of real displays. A wide -color -gamut display driven by an FPGA is used to emulate the color imetric response of real display devices. By changing the look -up tables in the FPGA, the virtual display emulates various real displays for testing different color calibrati on kits. Our experimental data for 6 real displays show that the virtual display ca n emulate real displays reasonably well. The results demonstrate that the proposed virtual display approach is a fast, economical, and objective method for evaluating the performance of color calibration kits. Keywords: Color calibration kit, FPGA, primar y stability, color management, color display, medical display.

Evaluating color performance of whole-slide imaging devices by multispectral-imaging of biological tissues

The color reproducibility of two whole-slide imaging (WSI) devices was evaluated with biological tissue slides. Three tissue slides (human colon, skin, and kidney) were used to test a modern and a legacy WSI devices. The color truth of the tissue slides was obtained using a multispectral imaging system. The output WSI images were compared with the color truth to calculate the color difference for each pixel. A psychophysical experiment was also conducted to measure the perceptual color reproducibility (PCR) of the same slides with four subjects. The experiment results show that the mean color differences of the modern, legacy, and monochrome WSI devices are 10.94±4.19, 22.35±8.99, and 42.74±2.96 ▵E00, while their mean PCRs are 70.35±7.64%, 23.06±14.68%, and 0.91±1.01%, respectively.

Comparison of methods for quantitative evaluation of endoscopic distortion

Endoscopy is a well-established paradigm in medical imaging, and emerging endoscopic technologies such as high resolution, capsule and disposable endoscopes promise significant improvements in effectiveness, as well as patient safety and acceptance of endoscopy. However, the field lacks practical standardized test methods to evaluate key optical performance characteristics (OPCs), in particular the geometric distortion caused by fisheye lens effects in clinical endoscopic systems. As a result, it has been difficult to evaluate an endoscope’s image quality or assess its changes over time. The goal of this work was to identify optimal techniques for objective, quantitative characterization of distortion that are effective and not burdensome. Specifically, distortion measurements from a commercially available distortion evaluation/correction software package were compared with a custom algorithm based on a local magnification (ML) approach. Measurements were performed using a clinical gastroscope to image square grid targets. Recorded images were analyzed with the ML approach and the commercial software where the results were used to obtain corrected images. Corrected images based on the ML approach and the software were compared. The study showed that the ML method could assess distortion patterns more accurately than the commercial software. Overall, the development of standardized test methods for characterizing distortion and other OPCs will facilitate development, clinical translation, manufacturing quality and assurance of performance during clinical use of endoscopic technologies.

eeDAP: an evaluation environment for digital and analog pathology

Purpose: The purpose of this work is to present a platform for designing and executing studies that compare pathologists interpreting histopathology of whole slide images (WSI) on a computer display to pathologists interpreting glass slides on an optical microscope. Methods: Here we present eeDAP, an evaluation environment for digital and analog pathology. The key element in eeDAP is the registration of theWSI to the glass slide. Registration is accomplished through computer control of the microscope stage and a camera mounted on the microscope that acquires images of the real time microscope view. Registration allows for the evaluation of the same regions of interest (ROIs) in both domains. This can reduce or eliminate disagreements that arise from pathologists interpreting different areas and focuses the comparison on image quality. Results: We reduced the pathologist interpretation area from an entire glass slide (≈10-30 mm)2 to small ROIs <(50 um)2. We also made possible the evaluation of individual cells. Conclusions: We summarize eeDAP’s software and hardware and provide calculations and corresponding images of the microscope field of view and the ROIs extracted from the WSIs. These calculations help provide a sense of eeDAP’s functionality and operating principles, while the images provide a sense of the look and feel of studies that can be conducted in the digital and analog domains. The eeDAP software can be downloaded from code.google.com (project: eeDAP) as Matlab source or as a precompiled stand-alone license-free application.

Impact of solid-state lighting on observer performance of color discrimination

We studied the impact of the microscope light source on readers performance using a microscopic version of the Farnsworth-Munsell 100 hue test for photographic slide film. Each pair of two adjacent color caps in the original test kit was reproduced on the film with random order and a 5X objective was used to examine the microscopic color patterns. The subjects visual task was to determine whether the color pair was in the correct hue order or not. The test was repeated for both a light-emitting diode lamp and a conventional halogen lamp. In this paper, we discuss the methodology using preliminary results.

P-4: A Reconfigurable Stereomicroscopic Imaging System for Digital Pathology

A reconfigurable stereomicroscope system consisting of exchangeable light source, condenser, objectives, cameras, and 3D display was designed to allow the user to adjust the convergence angle, magnification and color rendering arbitrarily. To evaluate the depth resolution of the proposed 3D system, miniature 3D models were used as test patterns in psychophysical experiments.