Flexible method to obtain high sensitivity, low-cost CCD cameras for video microscopy

A simple method is described to extend image exposure times in video-rate CCD cameras and thereby, increase their sensitivity and reduce noise level of low-light images. Most commercial video cameras lack the capability of extending image exposures since they operate regular television timing formats. The technique described here implements the control of the exposure times by selectively gating the image readout from the CCD sensor. This prevents the cyclic clearing of photo-charges occurring at regular video-rates, allowing image integration beyond the duration of single video field periods. Image readout is controlled by the duration of external gating pulses, giving the camera an efficient operational versatility under different light conditions. This technique is applicable to standard monochrome and color CCD cameras. The evaluations described here using this technique show that the light sensitivity of an standard video-rate CCD camera can be significantly improved, generating high quality images at low-light levels. These were comparable to those obtained with image intensifiers or intensified video cameras. Cameras are still compatible with regular video equipment, since this technique preserves the normal TV synchronization signals. Results in simulated and real experimental situations confirmed that this technique enables the use of affordable video-rate CCD cameras for a variety of fluorescence microscopy and optical recording applications.