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c. Image Capture
The optimised and standardised acquisition protocols for the capture of reflected and photo¬
induced luminescence images resulting from the iterative process described in Chapter 1 are
detailed in the following sections. In formulating these protocols, the sequence in which each
of the image sets are captured was also considered in order to facilitate workflow, but also to
ensure that all the post-processing requirements for each image set were collected. By
comparing the equipment and post-processing requirements for each of the imaging
techniques (Table 2-2), it can be observed that these divide themselves into a number of
natural groups. The equipment requirements column only notes the light sources and the
filters used, as all the other equipment is used in all of the techniques, but it is evident that
pairing the techniques which use the same light sources is an efficient way of proceeding. In
addition, the post-processing requirements column notes the images employed by each
image correction procedure and highlights the order in which the workflows should be
completed to ensure that the post-processing requirements for each workflow are met.
These considerations have resulted in the recommended sequence shown in Table 2-2.
The reproducibility of the images obtained has been at the forefront of the development of
the acquisition protocols. An important step towards such reproducibility is the recording of
all aspects of the experimental set-up and parameters used, in order that these may be
referred to for images taken both within the same institution by different users or at different
points in time and between institutions. The metadata to accompany the image sets acquired
should include the following for each of the workflows:
1) Information on the illumination conditions used, namely:
a) Make, model and spectral output distribution of the radiation sources;
b) Distance between the object and the radiation sources;
c) Height of the radiation sources;
d) Angle between the normal to the object and the direction of the incident radiation;
e) Irradiance (as a setting or light meter measurement);
(f) Colour temperature;
2) The make and model of the camera and lenses used and any modifications made to this
equipment;
3) The make, model and transmittance characteristics of the filter or filter sets used, both in
front of radiation source and in front of the camera.
And for each frame taken this should additionally include:
The ISO speed chosen;
The aperture value (F -stop) used;
The shutter speed (exposure time);
Any white balance settings used;
The number of that frame in the series.
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These are included as a checklist at the end of each image capture workflow. Additionally,
the frame should be the same for all technical images, as this will facilitate the processing
and comparison of the multispectral image set.
Version No. 1.0 64 Date : 14/10/2013