Stranica 49 [49]
OCR
2. Experimental Set-up The experimental factors and physical phenomena leading to the observation of spurious effects or device-dependent issues in multispectral images were discussed in Chapter 1. A number of workflows were proposed for both reflected and photo-induced luminescence images, which detailed the corrections reguired and the general transformations to be carried out by the post-processing software (see Chapter 1, Figures 17-18 and 27-28). The development and operation of this software will be discussed in more detail in Chapter 3, but the reguirements of the software in order to carry out the image correction procedure are central to the development of the acquisition protocols. As a result, work to develop optimised and standardised acquisition protocols which permitted the raw image data to be collected in the manner required, was undertaken in parallel with work on the development of post-processing methods. The optimised and standardised acquisition protocols for the capture of reflected and photo-induced luminescence images resulting from this iterative process are detailed in this Chapter. The development of these protocols began with an understanding of the function that each equipment component must carry out within the experimental set-up. The following sections discuss each of these components in more detail and the particular properties required in order to carry out these functions and acquire each of the multispectral imaging sets considered. A discussion of the set-up of this equipment in order to minimise experimental sources of error and the effect of physical phenomena follows. Finally, the five workflows for the optimised and standardised acquisition of the multispectral image sets discussed are described. A checklist of the requirements for the image correction procedure is included at the end of each workflow. A workflow for the optimised and standardised acquisition of visible-induced visible luminescence images is also included, although the post-processing of this image type is outside the scope of this work. a. Equipment selection The experimental set-up for the acquisition of multispectral images can be considered as being made up of a number of equipment components as shown in Figure 2-1: 1) A pair of radiation sources which provide the incident radiation to the object being studied and in the case of luminescence techniques also provide the means to induce the luminescence (the excitation source) in the materials under study; 2) A filter or set of filters in order to allow the transmittance of radiation in the wavelength range under study and exclude unwanted radiation from being recorded; 3) A detector or recording device which in this work is a commercially available digital camera with a silicon-based sensor, modified by removal of the IR-blocking filter to provide sensitivity from approximately 350 nm to 1100 nm; 4) A set of standards to enable the post-processing methods discussed in Chapter 1 and detailed in Chapter 3. Version No. 1.0 41 Date : 14/10/2013
