MEASUREMENT OF ROOT LENGTH AND THICKNESS USING A HAND-HELD COMPUTER SCANNER

A hand-held computer scanner was used to produce images of lines randomly drawn on a sheet of paper which could simulate roots. The binary images were analysed for total length using the intercept method and distribution of line thicknesses. The number of intercepts was normalized with respect to image size and resolution. This value, in conjunction with the fraction of line cover in the image, was used to obtain an equation to predict length (normalized with respect to picture size) from number of normalized intercept counts. The derived calibration equation (r2 = 0.998, cv = 1.7%) predicted the length irrespective of thickness and distribution of thickness. The intercept method was extended to determine the length of lines with different thicknesses within the image. It was possible to resolve line thickness differences of 0.15 mm for thickness ranging from 0.15 to 0.7 mm. Although the total length, determined as the cumulative length of all thickness intervals, was lower than the real total length, the relative distribution of thicknesses was accurate to 2%. From length and thickness of lines in each interval, its surface area could be calculated, assuming a cylindrical shape. The major advantages of using a hand-held scanner for root length determinations are: (i) very low cost, compared to other image analysis systems; (ii) high resolution (> 0.063 mm); (iii) actual size of the images is automatically recorded; (iv) small size of the scanner; and (v) image size is independent of the video screen size.