Characterization of Digital Cameras for Reflected Ultraviolet Photography; Implications for Qualitative and Quantitative Image Analysis During Forensic Examination

Abstract

Reflected ultraviolet imaging techniques allow for the visualization of evidence normally outside the human visible spectrum. Specialized digital cameras possessing extended sensitivity can be used for recording reflected ultraviolet radiation. Currently, there is a lack of standardized methods for ultraviolet image recording and processing using digital cameras, potentially limiting the implementation and interpretation. A methodology is presented for processing ultraviolet images based on linear responses and the sensitivity of the respective color channels. The methodology is applied to a FujiS3 UVIR camera, and a modified Nikon D70s camera, to reconstruct their respective spectral sensitivity curves between 320 and 400 nm. This method results in images with low noise and high contrast, suitable for qualitative and/or quantitative analysis. The application of this methodology is demonstrated in the recording of latent fingerprints.

Trade-off between camouflage and sexual dimorphism revealed by UV digital imaging: the case of Australian Mallee Dragons (Ctenophorus fordi)

“…S2). Camera responses corresponding to the red channel are produced by radiation within 325-395 nm to which this channel is highly sensitive (Garcia et al, 2013).…”

“…2) were obtained in a two-step process. First, the uncompressed RGB-TIFF images were split into their three component monochrome images, corresponding to the 'red', 'green' and 'blue' colour channels, only retaining those images corresponding to the red channel for further processing (Garcia et al, 2013). Subsequently, the linear sensor response at each pixel location was recovered by inverting, by numerical methods, a biexponential function describing the Opto-Electronic conversion function (OECF) for the red channel of the camera.…”

“…The first variable describes the spectral characteristics of the UV-reflective elements of the pattern as the total amount of UV reflected within a 325-390 nm spectral interval, expressed as linear pixel intensity values, corresponding to the spectral sensitivity of the red channel of the modified Nikon D70s camera (Garcia et al, 2013). Variables ii-iv measure different aspects of the spatial characteristics of the UV-reflecting elements of the pattern in terms of size and number.…”

“…Furthermore, with the recent advent of digital cameras with extended sensitivity into the UV region (Pike, 2011), it is now possible to obtain an objective measurement of the spectral and spatial properties of a colour pattern in this spectral region (Garcia et al, 2013).…”

Hot Shoes in the Room: Authentication of Thermal Imaging for Quantitative Forensic Analysis

“…There are many examples of the use of imaging techniques to record reflected visible (400-700 nm) [1] and invisible radiation, including ultraviolet-A (UVA) (320-400 nm) [2] and near-infrared (NIR) (780-1200 nm) [3], for visualising and collecting information useful as evidence in court rooms [3,4]. However, an important consideration for the use of evidence that might be relied upon by an expert to present an opinion in a court room scenario is that such evidence should be based on well-founded and repeatable scientific principles [1,5,6].…”