Figure below shows an example of a complete flexible video endoscope system. It consists of the light source, the video endoscope, the video processor, and the video monitor. Electronics involved include controlling electronics for the CCD detector located right behind the objective at the distal tip, electronics in the light source to provide power supply to the lamp (usually a high pressure Xenon arc bulb) and to control the air/water supply, imaging acquisition, and processing electronics in the video processor, and display electronics in the monitor.
For a fiberoptic endoscope based system, a color CCD video camera is often connected to the endoscope eye piece for image acquisition and electronic display on a monitor, replacing the traditional visual observation through the eyepiece using the endoscopist’s naked eye.
Besides providing electrical power supply to the lamp, the electronics in the light source also perform other duties and functions, such as light-level control, storing illumination settings, air/water pump control, and driving cooling fans. Electronics in a light source for a video endoscope may also involve controlling a rotating filter wheel to provide sequential red (R), green (G), blue (B) illumination and provide synchronization signals to the CCD control electronics.
Electronic white light color images for endoscopy can be obtained in two different ways: the sequential RGB imaging method and Bayer filtering method. In the sequential RGB imaging method as illustrated in Figure below, a rotating filter wheel is used in the light source to generate blue (B: 400–500 nm), green (G: 500–600 nm), and red (R: 600–700 nm) colored light sequentially, while a CCD detector sensitive to all visible wavelengths (at least covering 400–700 nm) is used to capture the R, G, and B images sequentially. To achieve video rate imaging, the wheel is rotated at 25 or 30 Hz according to different video standards. There are opaque blocks between the three filters to prevent mixed color light exposure and sequential RGB imaging data readout can be performed during these time periods.
Three memory boards may be used to store the three R, G, and B images. The digital images could then be converted into video signals for image display on a video monitor. This imaging method is often used in video endoscopy, facilitating a smaller CCD detector that helps miniaturization or gives higher resolution.
In the Bayer filtering method as illustrated in Figure below, a single hot mirror filter is used to simply generate a broad band white light (400–700 nm) illumination, while color imaging is realized by placing a Bayer filter mosaic on top of the CCD array. In a Bayer filter mosaic, each quartet of pixels utilizes three different filters for color separation. To match the human eye response one pixel filter transmits only red light, one pixel transmits only blue light, and two transmit only green (see Figure).
This filter overlays the CCD pixels with one-to-one correlation; in other words, when the detector captures an image, simultaneously 25% of the pixels capture red wavelengths, 25% capture blue wavelengths, and 50% capture green wavelengths. The resultant data is processed using color-space interpolation algorithms to create an RGB color image. In this imaging method, the resolution is degraded or a larger CCD detector is required to keep the same resolution. The advantages are simplicity and reduced cost for the complete endoscopy system. It is often used for electronic image acquisition and display in a fiberoptic endoscopy system, but could be used in video endoscopy as well.