PrimeEnhance 2D Active Image Deniosing Tech Note0 pages

Technical Note
CMOS, EMCCD AND CCD CAMERAS FOR LIFE SCIENCES

PrimeEnhance™
2D Active Image Denoising
There are several sources of noise when imaging faint signal
levels which can affect the Signal-to-Noise Ratio (SNR) of
your measurement, the main types being dark noise, read
noise and shot noise. Camera manufacturers make design
choices to minimize the presence of noise in the image and
to maximize the quality and SNR of the collected images.
Dark Noise is reduced by cooling the sensor, and read noise
is minimized through sensor performance and electronic
design.
Photon shot noise however, is an inherent property of
light. There is always a statistical variation in the number
of photons (or photoelectrons) detected in a given time
period. This uncertainty is dependent on the amount of
signal photoelectrons being measured and has the statistical
property of a Poisson distribution. This relationship is
expressed as:

Shot Noise = √Signal
While shot noise increases with signal, it increases more
slowly (as the square root). This results in SNR improving
with light levels. At low light levels, SNR is low even with a
perfectly acquired image.

Signal Level

Shot Noise

(e-)

(e- RMS)

5

2.23

44.8%

10

3.16

31.6%

50

7.07

14.1%

100

10

10%

500

22.36
31.62

•t Increase the exposure time and collect signal
for a longer time
t This allows for a higher signal level, reducing the
impact of shot noise. The ability to image at a
desired frame rate may be sacrificed, and the cell is
illuminated for a longer time, increasing phototoxicity
and photobleaching. Finally, if the exposure time is
long enough, the noise from dark current can become
a larger portion of the signal.
•t Average frames to reduce noise
t This allows for a reduction in total image noise as a
square root of the number of frames averaged. The
ability to image at adequate frame rates will again be
sacrificed, and is generally less productive than simply
increasing exposure time.
•t Increase the excitation intensity
t This allows for a higher signal level without
trading off temporal resolution. The rate at which
phototoxicity and photobleaching occurs is also
increased, reducing cell viability.

4.5%

1000

At these lower signal levels, there have been only a few
ways to improve SNR, each with a tradeoff.

3.2%

Percent of Signal

A remaining technique for the reduction of noise is
the use of a “denoising algorithm” that dynamically
examines the image collected in order to separate and
remove noise. The Prime camera from Photometrics
introduces a new real-time method for dynamic noise
reduction called PrimeEnhance.

Table 1

Rev A0-10052015

©2015 Photometrics. All rights reserved.

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