In an Active Pixel Sensor (=APS) Complimentary Metal Oxide Semiconductor chip each photodiode (pixel) is coupled to an individual amplifier. Also there is one A/D converter for each column of pixels so that the data of a row of amplifiers can be read out in parallel. The individual amplifiers lead to an overall reduction of noise, however, fixed pattern noise artefacts are induced, at least in early generation CMOS sensors, because of variations in amplifier gain and offset across the chip. Advantages of these devices are the possibility of pixel-wise gain manipulation and true region-of-interest readout. (In CCD cameras lines that contain pixels of a region-of-interest have to be read out entirely.) Also, it is possible to realize non-linear response curves, for example a logarithmically compressed voltage conversion, in order to achieve an increased intrascene dynamic range. A fundamental difference to CCD chips is further that here incoming photons remove electrons from charged capacitors instead of creating electrons in empty ones. A consequence is relatively high noise at low light levels which is detrimental for fluorescence imaging and one of the reasons for which CMOS cameras are not widespread in this field.