PrimeEnhance 2D Active Image Deniosing Tech Note
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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 • Increase the exposure time and collect signal for a longer time 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. • Average frames to reduce noise 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. • Increase the excitation intensity 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. At these lower signal levels, there have been only a few ways to improve SNR, each with a tradeoff. 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. ©2015 Photometrics. All rights reserved.

2D Active Image Denoising Technical Note PrimeEnhance There are many challenges when processing data to reduce noise such as preserving the quantitative nature of the recorded pixel intensities, as well as preserving key features like edges, textures and details with low contrast. Further, processing has to be accomplished without introducing new image artifacts like ringing, aliasing or blurring. Many algorithms are inflexible with different image types, resulting in these intrusive artifacts. Additionally, because noise tends to vary with the level of signal, it is difficult for many...

2D Active Image Denoising Technical Note A difference image (Fig 1c) between the original and PrimeEnhance image shows that only noise has been removed by PrimeEnhance, with the brighter regions showing higher noise levels in keeping with the relationship discussed in the introduction. Figure 2a and 2b provide an increased zoom level on the structures within the cell, and show that features are preserved while no artifacts have been generated. The line profiles demonstrate PrimeEnhance’s ability to reduce the shot noise present in the image, extracting features that were previously...

2D Active Image Denoising Technical Note PrimeEnhance Experimental Impact By increasing the effective signal to noise in each frame, it is possible to acquire high quality images at lower exposure times, reducing the effects of phototoxicity and photobleaching on samples. The following are images acquired of a faint samples with a 100ms exposure compared to images150 acquired with an 800ms exposure. 0 140 The comparison between the 800ms exposure and the 100ms PrimeEnhance exposure, as evidenced by the line-profiles, 140 135 demonstrates the increase of image and data quality possible with...