Stranica 87 [87]
(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- M 66)
stop number) = 11.98
(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 2-29
retaken.
White balance
16) Note that the image of the uniform reflective board can also be set as the custom white
balance if reguired. Follow the manufacturers instructions for the camera model in use.
17) Otherwise the white balance can be setto a camera standard preset corresponding to
the illumination source being used, (e.g 6500K or equivalent). Note that the correct
setting here is not crucial as this can always be modified in post-processing (see
Chapter 3).
O btain the UV-reflected image
18) Set up the image by using either the eyepiece or preferably the live view mode on the
screen if this is available.
19) 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 when the UV bandpass filter is in front of the
lens.
20) Take the image.
Evaluate the UV-reflected image
21) Check the framing by looking at the image in playback mode.
22) Check the focus by zooming into the image in playback mode.
23) Check the exposure.
24) Check the tonal range by checking the image histogram in playback mode.
Version No. 1.0 79 Date : 14/10/2013