Noise effects and filtering in controlled light exposure microscopy.

Phototoxicity and photobleaching are major limitations of fluorescence live-cell microscopy. A straightforward way to limit phototoxicity and photobleaching is reduction of the excitation light dose, but this causes loss of image quality. In confocal fluorescence microscopy, the field of view is illuminated uniformly whereas in controlled light exposure microscopy, illumination is controlled per pixel on the basis of two illumination strategies. The controlled light exposure microscopy foreground strategy discriminates between bright and weak foreground. Bright foreground pixels are illuminated with a reduced light dose resulting in limited excitation of fluorophores and consequently limited phototoxicity and photobleaching. The controlled light exposure microscopy background strategy discriminates between foreground and background. Pixels that are judged to be background are also illuminated with a reduced light dose. The latter illumination strategy may introduce artefacts due to the stochastic character of photon flow. These artefacts are visible as erratic 'darker pixels' in the foreground with a lower pixel value than the neighbouring pixels. This paper describes a special adaptive image processing filter that detects and corrects most of the 'darker pixels'. It opens the possibility to use controlled light exposure microscopy even in high noise (low signal to noise ratio) imaging to further reduce phototoxicity and photobleaching.