Endoscopes are used by almost every medical specialty: gastroenterology, pulmonology, gynecology, urology, orthopedics, anesthesia, ENT, thoracic surgery, and general surgery. Color plays an important role in endoscopic  as well as in laparoscopic  imaging. The main purpose of endoscopy/laparoscopy is to visualize a certain object inside the human body, such as internal organs, from outside. To visualize the internal organs, one must deliver the light into the human body to shine the object, image the scene, transmit the image data back to the outside, and finally reproduce the image for human readers. Normally, internal organs in vivo are not visible by a naked eye because the human body blocks visible light. Thus, the key of various endoscopy and laparoscopy technologies is to get around the barrier such that the light can be delivered and the image can be retrieved. Different devices address this problem with different approaches: the straightforward method is to perform surgery (e.g., thoracic or general) and gain direct access to the object. Laparoscopy is a less intrusive alternative to surgery. Endoscopy gains access through the cavities of the human body.
Conventionally, a tubular device is used to house both the light delivery channel and the image retrieval channel for either passing through or getting around the barrier. Capsule endoscopy takes advantage of the open circuit of the human gastrointestinal tract. The capsule travels the gastrointestinal tract passively while capturing and storing the images autonomously. Table 1 compares various endoscopic and laparoscopic methods by parameterizing each component in the imaging chain with examples.
A critical aspect for identifying color-related issues in endoscopic and laparoscopic systems is a review of the makeup of the imaging chain. The generalized imaging chain consists of object, illumination, light guide, detector, image guide, intermediate image or video file, video processor, display, and human reader. In laparoscopy systems, the illumination source is typically a xenon lamp. In endoscopy, the illumination source can be xenon/halogen light, filtered narrow-band light guided by a fiber optic bundle at the proximal end, or light-emitting diode lights embedded at the distal end. The endoscope itself can be rigid, flexible, or in a capsule form. The image detector can be an external video camera at the proximal end, or an embedded camera at the distal end. While most flexible endoscopes transmit image data electrically via internal wires, capsule endoscopes can transmit image data electrically via human body, electromagnetically via radiofrequency signaling, or physically via memory storage. The capsule systems also require the image data to be saved as intermediate files for off-line processing and review. The video data is rendered by the video processor in real time for flexible endoscopes, or off line for capsule endoscopes. The video data is presented to the endoscopist by an electronic display device during the procedure and can be archived in a picture archiving and communications systems (PACS) or as part of the electronic medical record (EMR) system for future review.
In these modalities, it is important to clarify related topics: color reproducibility, color consistency, color characterization, and color standardization. Color reproducibility means that the original scene can be faithfully reproduced, either colorimetrically or perceptually, on the final display. Color consistency means that the relationship between the input scene and the output image (i.e., the color mapping) remains constant. Color characterization means to measure and to determine the relationship between the input and output of a component/system with a certain color target. Color standardization means that the input and output of a component in the imaging chain are well defined such that products from different vendors are interchangeable (i.e., interoperability).
Surgeons who perform both open surgery and laparoscopic surgery may see slight differences in color when observing the same tissue. During open surgery, the surgeon looks at the tissue directly with his/her naked eyes while the tissue is illuminated by the lighting in the operating room. During laparoscopic surgery, the same surgeon observes the same tissue via the laparoscope and can therefore compare the color of the laparoscopic image to his/her recollection of how the tissue appeared when viewed directly with the naked eye. However, in a video-based (e.g., flexible or capsule) endoscopic procedure, the endoscopist observes a reproduced electronic image of the object illuminated by a nonstandard light source. If the endoscopist does not normally see this same tissue with his/her naked eye, but always uses an endoscope, the endoscopist believes the true color of the tissue is similar to the endoscopic image. Results from surveys of endoscopists and laparoscopists described at the Summit demonstrate that although a true color match between real-life color and the color on the display appears to be more important for laparoscopy than for endoscopy, most participants agreed that color standardization is beneficial for the advancement of the technology and its clinical applications. However, no misdiagnoses have been reported due to unfaithful color reproduction. Endoscopists rely on a pathologist’s examination of the endoscopic biopsy for the diagnosis. Therefore, nonideal color reproducibility of endoscopy/laparoscopy devices does not lead to safety concerns.
Achieving color reproducibility remains difficult since current endoscopes cannot emit light evenly yielding color variations with brightness. To date, the design goal of current endoscopy systems is not color reproducibility but user preference. In addition, since determining the original scene with existing endoscope products is not feasible, one can use the image shown by the onsite display to the endoscopist for establishing the diagnosis truth. However, color characterizing the onsite display is also challenging (see the Medical Display Section) and providing an identical or similar image on other display devices remains difficult even with a modification of the digital imaging and communications in medicine (DICOM) standard. This level of color consistency for the display of color images requires characterizing the input and output devices and adding new tags into the DICOM or ICC format, which are feasible but practically challenging. Current devices include quality assurance/quality control (QA/QC) procedures and criteria not based on the original scene but on the color consistency requirements imposed by the manufacturers.
In summary, color standardization is not critical in endoscopy if the components of the system are from the same vendor and managed within a unique framework. When systems consist of varying components or devices from different vendors, standardization should be helpful for achieving consistency. Even though the laparoscopic system is also designed in the same manner, it is physically possible to be composed of mix-and-match components from different vendors and thus color standardization would be preferred. In addition, color standardization is important if color consistency is required when endoscopy video is archived or recorded for future review with identical or completely different systems. Overall, faithful color reproduction is technically challenging for these modalities and currently not in demand by the user community.