Comparative signal to noise ratio as a determinant to select smartphone image sensor colour channels for analysis in the UVB

Igoe, D. P. and Parisi, A. V. and Downs, N. J. and Amar, A. and Turner, J. (2018) Comparative signal to noise ratio as a determinant to select smartphone image sensor colour channels for analysis in the UVB. Sensors and Actuators A: Physical, 272. pp. 125-133. ISSN 0924-4247


The signal to noise ratio (SNR) is an important consideration for any scientific image sensor application, particularly the relatively low light involved with observations of the solar disc at a discrete ultraviolet-B (UVB) wavelength using an unmodified smartphone image sensor. In particular, the SNR of each of the primary image sensor colour channels (red, green and blue) is a critical step in determining which colour channel signal to analyse for any characterisation research. In each image, the solar disc appears as a very small pale-magenta dot. In this paper, the SNR of each colour channel response for solar UVB, alongside their chromatic transforms were analysed for a stacked, mosaic filtered, backside illuminated complementary metal oxide semiconductor (CMOS) image sensor. Using data visualisation techniques, it has become clear that specific colour channels, in this case – the red channel, provide the strongest SNR for use in characterisation and other analytical research. The effects of a straightforward adaptive threshold and de-noising algorithm (median filter) on each colour channel’s SNR are also analysed. The variation of the colour channels’ SNR with external factors, including irradiance, is modelled. The effects of the prevalence of noise features, such as hot pixels and dark noise, are also observed. It has been found that before the median filter is applied, most of the signal, particularly for the green colour channel, is from these noise features in some image sensors – representing a ‘false positive’ in these low-light conditions. A chrominance model using a weighted proportion of the red and blue colour channels that provides the best SNR when sensing in the UVB waveband for the sensor has been developed and evaluated.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Access to published version in accordance with the copyright policy of the publisher.
Faculty / Department / School: Current - Faculty of Health, Engineering and Sciences - School of Agricultural, Computational and Environmental Sciences
Date Deposited: 19 Feb 2018 00:06
Last Modified: 15 May 2018 00:02
Uncontrolled Keywords: signal-to-noise ratio; UVB; complementary metal oxide semiconductor; denoising algorithm; adaptive threshold; image integrity
Fields of Research : 02 Physical Sciences > 0299 Other Physical Sciences > 029999 Physical Sciences not elsewhere classified
Socio-Economic Objective: E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Identification Number or DOI: 10.1016/j.sna.2018.01.057

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