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15) Check the image exposure. The RGB values of the image on the image histogram (Figure 2-32) in playback mode are a good indicator but note that these values pertain to the preview J PEG generated by the camera not the RAW data (see Chapter 3). (a) The RGB values must not exceed 255 grey levels. (b) If any of the pixels are saturated either: — Move the radiation sources further away from the subject — Stop down the aperture (increase the f-stop M 66) number) EM 11.6MB (c) Retake the image until it is not saturated. 121/122 (d) Note that if the lighting conditions or geometry change, this image should be Figure 2-32 retaken. White balance 16) Set the white balance to 6500K (or equivalent). Follow the manufacturers instructions for the camera model in use. Obtain the UV-induced visible luminescence image 17) Set up the image by using either the eyepiece or preferably the live view mode on the screen if this is available. 18) If using the live view mode, adjust the focus by zooming all the way into the frame. It may be useful to use a UV LED torch to illuminate the object whilst focussing as the image on screen can appear quite dark. 19) Take the image. Evaluate the UV-induced visible luminescence image 20) Check the framing by looking at the image in playback mode. 21) Check the focus by zooming into the image in playback mode. 22) Check the exposure. 23) Check the tonal range by checking the image histogram in playback mode. Record the metadata for the UV-induced visible luminescence workflow and image(s) 24) Record the following information for the workflow: (a) Information on the illumination conditions used, namely: Make, model and spectral output distribution of the radiation sources; Distance between the object and the radiation sources; Height of the radiation sources; Version No. 1.0 84 Date : 14/10/2013
