Median filters as a tool to determine dark noise thresholds in high resolution smartphone image sensors for scientific imaging
Article
Article Title | Median filters as a tool to determine dark noise thresholds in high resolution smartphone image sensors for scientific imaging |
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ERA Journal ID | 1033 |
Article Category | Article |
Authors | Igoe, Damien P. (Author), Parisi, Alfio V. (Author), Amar, Abdurazaq (Author) and Rummenie, Katherine J. (Author) |
Journal Title | Review of Scientific Instruments |
Journal Citation | 89 (1), pp. 1-8 |
Article Number | 015003 |
Number of Pages | 8 |
Year | 2018 |
Place of Publication | United States |
ISSN | 0034-6748 |
1089-7623 | |
1527-2400 | |
Digital Object Identifier (DOI) | https://doi.org/10.1063/1.5006000 |
Web Address (URL) | https://pubs.aip.org/aip/rsi/article-abstract/89/1/015003/932178/Median-filters-as-a-tool-to-determine-dark-noise?redirectedFrom=fulltext |
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. |
Keywords | Smartphone; hot pixels; median; filter; dark noise; UV |
Contains Sensitive Content | Does not contain sensitive content |
ANZSRC Field of Research 2020 | 519999. Other physical sciences not elsewhere classified |
Public Notes | File reproduced in accordance with the copyright policy of the publisher/author. |
Byline Affiliations | Faculty of Health, Engineering and Sciences |
Institution of Origin | University of Southern Queensland |
https://research.usq.edu.au/item/q7048/median-filters-as-a-tool-to-determine-dark-noise-thresholds-in-high-resolution-smartphone-image-sensors-for-scientific-imaging
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