The noise-based speed is defined as the exposure that will lead to a given signal-to-noise ratio on individual pixels. Two ratios are used, the 40:1 ("excellent image quality") and the 10:1 ("acceptable image quality") ratio. These ratios have been subjectively determined based on a resolution of 70 pixels per cm (178 DPI) when viewed at 25 cm (9.8 inch) distance. The signal-to-noise ratio is defined as the standard deviation of a weighted average of the luminance and color of individual pixels. The noise-based speed is mostly determined by the properties of the sensor and somewhat affected by the noise in the electronic gain and AD converter. COUNT 5
QSN1 Which ratios are employed to calculate noise-based speed? ANS1 the 40:1 ("excellent image quality") and the 10:1 ("acceptable image quality") ratio QSN2 What is the noise-based speed? ANS2 the exposure that will lead to a given signal-to-noise ratio on individual pixels QSN3 How are the two ratios found? ANS3 subjectively determined based on a resolution of 70 pixels per cm (178 DPI) when viewed at 25 cm (9.8 inch) distance QSN4 What is a definition of signal-to-noise ratio? ANS4 the standard deviation of a weighted average of the luminance and color of individual pixels QSN5 What factors influence the noise-based speed? ANS5 the properties of the sensor and somewhat affected by the noise in the electronic gain and AD converter