Afterward, each image was converted to RGB format and then
to 8 bits (grey level) using the software Image J 1.34s (National
Institute of Health, USA). In this format, a pixel area of 320 690
was selected at the center of the scanned image, and then
segmented using the Otsu algorithm, which produces highlyuniform
binary images (Otsu, 1979). The measurement of the
seven factors mentioned above was carried out with the software
SigmaScan Pro versión 5.0 (Systat Software Inc., San José California,
USA).