The first step in extracting the CRT from the raw images
involved the marking of the center of each blanching site at
the start of each recording. Since the blanching sites often
appear very faint, an exaggerated view of the image using
subsequent image information to facilitate the blanching
exaggeration was used (Fig. 1). Once all the start positions
were marked, the color of the blanching site was logged as it
changed with respect to time. Due to infant restlessness optical
flow tracking methods were applied to ensure that the
correct part of the scene was used as the blanching site. A
Shi-Tomasi corner detector was used to find corners in the
image and the Lucas-Kanade method was employed to
match the points of interest to the corresponding points in
subsequent frames [16]. This information was then used to
move the region of interest markers with the patient‟s skin.
Due to excessive motion and non-uniform lighting conditions
most of the data were rejected. The extracted color
information was then plotted with respect to time to allow
manual CRT selection to be performed to ensure that the
selected times were not compromised by unexpected artifacts
in the color data.