A prospective, controlled trial of eight-bit, 16-bit, and 24-bit digital color images in electronic endoscopy

Digital color information is obtained in "bits" or parcels of information for each color (red, green, blue) of a picture. As the number of bits increases, the amount of color information increases, and more colors can be displayed on a suitable monitor. With eight bits of information, 256 colors can be displayed; with 16 bits, several thousand colors can be displayed; and with 24 bits, more than 16 million colors can be displayed. We sought to determine the minimum requirement for diagnostic-quality endoscopy images in a prospective blinded trial.

Twenty-four bit color images were digitally acquired from the processor using a video card and a personal computer. Ten lesions were chosen to represent the gamut of lesions seen in the upper gastrointestinal tract. Images were simultaneously obtained with decreasing color information (16 and eight bits), and these served as controls. Eleven observers were the test subjects. Six endoscopy nurses, who perform color calibrations, and five endoscopists viewed the images. Eight-bit, 16-bit and 24-bit color images were coded and displayed simultaneously on a high-resolution color monitor (Supermac Technology, Sunnyvale, CA) that can display 16.8 million colors.

All images were considered to be of diagnostic quality by the observers, and the area of abnormality was identified and the diagnosis made in all cases. Of 110 viewings of the 24-bit image, on 45 occasions (41%) the viewers could detect no difference between it and the eight-bit and 16-bit images. In 23 (21%), the 24-bit color image was correctly recognized, and on 21 occasions (19%) the 24-bit image was incorrectly identified as eight-bit or 16-bit. Similar data were obtained with viewings of the eight-bit and 16-bit images.

Our results demonstrate that, with current endoscopic technology, 256 colors may be as good as 16 million. Eight-bit color is an acceptable image standard for routine endoscopy.