Abstract
A digital image can be created by taking input from a scanner. A scanner has a light source which illuminates a flat or nearly-flat object, which reflects differential intensities to a sensor, which registers intensities pixel-by-pixel, for input to a computer.
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Notes
- 1.
Invented in 1969 by Willard Sterling Boyle (1924–2011) and George Elwood Smith (born 1930) at Bell Laboratories, New Jersey, awarded Nobel prize for Physics 2009.
- 2.
- 3.
Scanner sizes are commonly in inch units. Metres = inches \(\times 0.0254\); inches = metres \(\times 39.37\); millimetres = inches \(\times 25.4\); inches = millimetres \(\times 0.0394\).
- 4.
In a CRT this is imposed by the physics of the electron guns. In an LCD, which works differently, the same function is imposed for compatibility with the once-dominant CRTs.
- 5.
Given a number N in the range \(N_{\min }\) to \(N_{\max }\), it is normalized in the range 0 to 1Â as
$$\begin{aligned} N_\mathrm {norm} = (N - N_{\min }) / (N_{\max } - N_{\min }) \,. \end{aligned}$$Given a number \(N_\mathrm {norm}\) normalized in the range 0 to 1, it is de-normalized in the range \(N_{\min }\) to \(N_{\max }\)Â as
$$\begin{aligned} N = (N_\mathrm {norm} \times (N_{\max } - N_{\min })) + N_{\min } \end{aligned}$$.
- 6.
In practice a perfect reflecting surface is never achieved: the best laboratory White surface (thick magnesium oxide newly-deposited on metal) reflects about 98Â % of incident light (density 0.009), and ordinary White paper about 85Â % (density 0.07). In practice, optical density is taken as relative to the current good-enough White.
- 7.
In practice a perfect absorbing surface is never achieved: the best laboratory Black surface (Black velvet) reflects about 0.0025Â % of incident light (density 2.6), and ordinary rough Black paper about 15Â % (density 0.82), or 8Â % (density 1.1) if glossy.
References
ITU-R Recommendation BT 709-5 (2008) Parameter values for the HDTV standards for program and international exchange. http://www.itu.int/rec/R-REC-BT.709/en. Accessed 1 Feb 2014
Open Directory (2014) Scanners. http://www.dmoz.org/Computers/Hardware/Peripherals/Scanners/. Accessed 1 Feb 2014
Poynton CA (2009) Color FAQ. http://www.poynton.com/ColorFAQ.html. Accessed 1 Feb 2014
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Parkin, A. (2016). 1-bit Scanner Input. In: Digital Imaging Primer. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-85619-1_22
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DOI: https://doi.org/10.1007/978-3-540-85619-1_22
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