Median filters as a tool to determine dark noise thresholds in high resolution smartphone image sensors for scientific imaging

Igoe, Damien P. and Parisi, Alfio V. ORCID: https://orcid.org/0000-0001-8430-8907 and Amar, Abdurazaq and Rummenie, Katherine J. (2018) Median filters as a tool to determine dark noise thresholds in high resolution smartphone image sensors for scientific imaging. Review of Scientific Instruments, 89 (1):015003. pp. 1-8. ISSN 0034-6748

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Abstract

An evaluation of the use of median filters in the reduction of dark noise in smartphone high resolution image sensors is presented. The Sony Xperia Z1 employed has a maximum image sensor resolution of 20.7 megapixels, with each pixel having a side length of just over 1 µm. Due to the large number of photosites, this provides an image sensor with very high sensitivity, but also makes them prone to noise effects such as hot-pixels. Similar to earlier research with older models of smartphone, no appreciable temperature effects were observed in the overall average pixel values for images taken in ambient temperatures between 5°C and 25°C. In this research, hot-pixels are defined as pixels with intensities above a specific threshold. The threshold is determined using the distribution of pixel values of a set of images with uniform statistical properties associated with the application of median-filters of increasing size. An image with uniform statistics was employed as a training set from 124 dark images and the threshold was determined to be 9 digital numbers. The threshold remained constant for multiple resolutions and did not appreciably change even after a year of extensive field use and exposure to solar ultraviolet radiation. Although the temperature effects uniformity masked an increase in hot-pixel occurrences, the total number of occurrences represented less than 0.1% of the total image. Hot-pixels were removed by applying a median filter, with an optimum filter size of 7 x 7, similar trends were observed for four additional smartphone image sensors used for validation. Hot-pixels were also reduced by decreasing image resolution. The method outlined in this research provides a methodology to characterise the dark noise behaviour of high resolution image sensors for use in scientific investigations, especially as pixel sizes decrease.


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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Faculty/School / Institute/Centre: Historic - Faculty of Health, Engineering and Sciences - School of Agricultural, Computational and Environmental Sciences (1 Jul 2013 - 5 Sep 2019)
Faculty/School / Institute/Centre: Historic - Faculty of Health, Engineering and Sciences - School of Agricultural, Computational and Environmental Sciences (1 Jul 2013 - 5 Sep 2019)
Date Deposited: 06 Mar 2022 23:43
Last Modified: 19 Jul 2022 00:53
Uncontrolled Keywords: Smartphone; hot pixels; median; filter; dark noise; UV
Fields of Research (2008): 02 Physical Sciences > 0299 Other Physical Sciences > 029999 Physical Sciences not elsewhere classified
Fields of Research (2020): 51 PHYSICAL SCIENCES > 5199 Other physical sciences > 519999 Other physical sciences not elsewhere classified
Socio-Economic Objectives (2008): E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Socio-Economic Objectives (2020): 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280120 Expanding knowledge in the physical sciences
URI: http://eprints.usq.edu.au/id/eprint/46789

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