sCMOS camera

A camera with scientific complementary metal oxide semiconductor (sCMOS) image sensor.  Unlike standard CMOS sensors, the pixel size is appropriate for scientific application such as microscopy and the data output is suitable for quantification.  In CMOS sensors each pixel has its own amplifier and readout circuitry.  The design of the amplifier circuitry in the sCMOS sensor results in high-speed operation with low noise.

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SNR(Signal to Noise ratio, S/N)

SNR is defined as the ratio of the total signal to the total noise. The signal to noise ratio (SNR) provides a value in predicting which camera performs best for certain applications, assuming the light levels for that application are known.

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In image sensors, smear is a phenomenon where a signal charge generated by intense input light leaks to the adjacent pixels or CCD transfer region and causes the original signal to become smeared (blurred). In contrast to “blooming” that occurs following saturation, smears occur even before saturation. Smears tend to occur from light at longer wavelengths rather than light at shorter wavelengths.

Spatial resolution

The ability of an image sensor to faithfully capture the details of an object. MTF (modulation transfer function) is usually used to evaluate the resolution of an image sensor. When an object with a sine-wave brightness distribution is imaged, the MTF indicates how the sine-wave brightness contrast varies with the spatial frequency. The spatial frequency is the number of times that a sine wave is repeated per unit length. Since the active area of an image sensor consists of discrete pixels, the sensor has a limiting resolution determined by the Nyquist limit based on the discrete sampling theorem. For example, when a black-and-white pattern is viewed with an image sensor, the difference between the black and white signal levels decreases as the pattern becomes finer, and finally reaches a point at which the pattern can no longer be resolved. The ideal MTF is expressed as follows: sinc* {(π x f ) / (2 x fn)} (f: spatial frequency, fn: spatial Nyquist frequency). However, because of the difficulty in creating an optical sine wave, a rectangular-wave response test chart is generally used instead. In this case, the spatial frequency response is called the CTF (contrast transfer function).


* sinc: Fourier transform of an ideal rectangular function


A setting in the camera where a subset of pixels is selected to define the image size by the number of horizontal and vertical pixels being scanned. Since less data is being readout and transferred, this method can offer increased frame rates with no increase in read noise. For a sCMOS camera, the readout rate is determined by the number of horizontal lines being scanned. Therefore, using a subarray with less vertical lines will decrease the readout time and increase the maximum frame rate. Unlike CCD sensors in which the areas outside of the ROI need to be transferred and discarded, the architecture of sCMOS sensors allows the read out of only the ROI itself. Because of this scheme, frame rates of the sCMOS sensor increase inversely to the number of pixels read out.