Pré-Publication, Document De Travail Année : 2019

Determination of light dose in a flat bed scanner using a gelatin silver bromide photographic paper

Jean-Paul Gandolfo
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Bertrand Lavédrine
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Résumé

This study presents an alternative way to evaluate the light exposure of document during scanning by measuring the density produced on unprocessed photographic paper. This method, requiring a densitometer and a black and white darkroom, has been applied to an office flat-bed scanner (Agfa Snapscan 600). For this scanner, the light dose depends on the choice of resolution and rang es from 6 to 25 lux.hours, that is to say, less than 30 minutes exposure under 50 lux. Introduction Early photographs and colour prints can be damaged by intense light exposure. Many recommendations have been published on this topic and the trend is to limit the display of fragile valuable documents. Most of the concerns focus on exhibitions, however artefacts might receive significant light exposure during conservation treatment, documentation, or digitization procedures. In the case of a static artificial light source, a luxmeter permits an evaluation of the illuminance. In the case of a scanner, the fluorescent tube source moves below the document during scanning and the use of a luxmeter is not appropriate. To address this question in a simple way, we scanned unprocessed photographic papers (Developing Out Paper: DOP) at different resolutions. From the value of the neutral optical densities obtained after processing , we could calculate the exposures (light doses) that produce identical darkening. The light dose received within the scanner is eventually given in lux.hours. Those values were then converted to an equivalent leng th of time at 50 lux illuminance.

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hal-02404289 , version 1 (11-12-2019)

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  • HAL Id : hal-02404289 , version 1

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Jean-Paul Gandolfo, Bertrand Lavédrine. Determination of light dose in a flat bed scanner using a gelatin silver bromide photographic paper. 2019. ⟨hal-02404289⟩
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