Wednesday, 06/02/2010 | High Dynamic Range Imaging with sCMOS (Scientific CMOS)
Kelheim (Germany), Belfast (Northern Ireland), Milpitas (USA), 23 July 2009 - Scientists are reporting that the new sCMOS technology is proving essential for scientific imaging applications because, for the first time, it is allowing for the accurate measurement of structures that are very dim as well as structures that are very bright in the same field of view. Having a camera system with a large dynamic range is therefore important for scientific imaging applications such as fluorescence microscopy.
In addition to this intra-scenic variation, inter-scenic variations in intensity also require a camera with a large dynamic range. An example of this is calcium ratiometric imaging where signals can vary greatly in intensity on a frame to frame basis.
The dynamic range in image sensors is defined as the pixel full well capacity divided by the smallest signal level that can be measured, which equals the readout noise. Therefore to improve the dynamic range both a large pixel full well and a small readout noise are beneficial. In order to utilize the full well of a CMOS pixel, the amplifier gain must be kept low. For example, given a 1.5V swing on the output of the amplifier, a 30,000 electron signal will require a gain of 1.5V/30,000e- = 50uV/e-.
This will allow measurement of the full well signal but will not allow for the lowest possible read noise. In order to get a very low readout noise and the resulting superior sensitivity, a value of 1500uV/e- would be ideal but this would mean that the largest signal would be limited to 1000e- maximum which is only 1/30th of the total well size.This leaves us with a quandary of whether to choose maximal sensitivity or good dynamic range imaging.
Andor Technology, Fairchild Imaging and PCO have taken together a novel design approach in sCMOS technology by using both approaches simultaneously. sCMOS technology has a high gain, high sensitivity amplifier to get the lowest possible noise on one output and a low gain amplifier for the largest possible signal on another output which are simultaneously read out and converted into digital valuesallowing both signals to be combined for a higher dynamic range signal.
As shown in the sCMOS white paper released on June 16th at the Laser World of Photonics show, both circuits incorporate high performance 11 bit ADCs to produce 2048 gray levels of significant data. Both outputs are sent to the camera which could either combine the data into one 16 bit image or leave it in two high quality data streams. This means, depending on the camera system, that a user could select high sensitivity data for one application, high signal data for another application or a combined high dynamic range data that maintains a good SNR for the low and the high end of the data range.
This approach allows the scientific user to get high quality linear data for both dim and bright targets within the field of view while getting unparalleled sensitivity due to the ultra-low noise of the readout. This combination makes the sCMOS technology a compelling solution for many scientific imaging applications.
Download the sCMOS White Paper.