Three primary undesirable signal components (noise), which degrade the performance of a CCD imaging device by lowering signal-to-noise ratio, are considered in calculating overall SNR : When the tutorial is initially loaded or is reset, the slider positions default to values that are typical for a high-performance scientific grade camera system utilizing a cooled CCD. Manipulation of the five sliders, in conjunction with the radio buttons adjacent to several, produces a range of signal-to-noise ratio values corresponding to most operating conditions likely to be encountered in the use of CCD cameras designed for low light imaging in microscopy. This value represents the product of photon flux, quantum efficiency, and integration time. The right-hand yellow numerical field ( Detected Photons/Pixel) displays the total number of signal photons read out by the CCD for each pixel over the integration period currently set by the slider. The photon noise contribution to total noise is a function of signal level and is not an independent noise variable that can be reduced through camera design or method of operation, but is accounted for in the SNR calculation. Sliders are provided for varying the CCD specifications for Read Noise (2 to 20 electrons rms per pixel) and for Dark Current (0.01 to 50 electrons per pixel per second). The Integration Time slider adjusts the CCD integration time over a range of 0.1 to 100 seconds. The Quantum Efficiency slider in the tutorial provides an adjustment range of 20 to 98 percent, and the Photon Flux slider allows selecting incident light levels between 0.0 photons per pixel per second. The product of these three variables determines the signal portion (numerator) of the signal-to-noise ratio, which is weighed against all noise sources that contribute to the denominator term of the ratio. The measured signal from a CCD imaging system, utilized in calculating SNR, depends upon the photon flux incident on the CCD (expressed as photons per pixel per second), the quantum efficiency of the device (where 1 represents 100 percent efficiency), and the integration (exposure) time over which the signal is collected (seconds). When the SNR is recalculated to reflect the binning operation, it is assumed that the signal is the same for each pixel within a group. The binning factor represents the number of pixels that are combined to form each larger pixel. The radio buttons labeled Binning Factor can be selected individually to enable a method of signal-to-noise ratio improvement commonly used with scientific CCD cameras, in which the signal-generated charge from groups of neighboring pixels is combined during readout into larger 'superpixels'. A large signal-to-noise ratio is important in the acquisition of high-quality digital images, and is particularly critical in applications requiring precise light measurements. Changes made to the factors that directly affect signal level, and to those variables primarily contributing noise to the system, have an inverse effect on SNR that is reflected in the displayed value. During image acquisition with electronic sensors, including CCDs, apparently random fluctuations in signal intensity constitute noise superimposed on the signal, and as the magnitude of noise increases, uncertainty in the measured signal becomes greater. As each variable is changed, the calculated value of signal-to-noise ratio is updated in the left-hand yellow box.

Parameters that affect signal-to-noise ratio for a CCD sensor can be varied for the system modeled in the tutorial by using the mouse to reposition any of the sliders located below the display window. The tutorial initializes with the display of a graphical plot of signal-to-noise ratio as a function of integration (exposure) time for a hypothetical CCD system with specifications typical of high-performance cameras used in microscopy imaging applications.

Camera temporal dark noise