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Sensitivity Analysis of Computer-Based Diameter Measurement from Digital Images

USDA-ARS-AFSRC, 1224 Airport Rd., Beaver, WV 25813

View larger version (18K): [in a new window]   Fig. 1. Length by diameter class (LD) curves for scanned image diameter estimation of 0.947 mm diameter wire at three resolutions, 15.2 p mm-1 (66 = 0.066 mm width pixels), 27.6 p mm-1 (36 = 0.036 mm width pixels), and 42.1 p mm-1 (24 = 0.024 mm width pixels). Data are the same as those in Fig. 3, sharpened- scan. Scanner setting: color photograph, high-resolution printer output, saved as tiff files. Diameter class size was set at 0.01 mm.

View larger version (24K): [in a new window]   Fig. 2. Scanner estimation of length of two wires (1.190 mm diameter, 0.95 m long; and 0.229 mm diameter, 1.12 m long) and hair (0.057 mm diameter and approx. 3 m long) with and without image sharpening. Images are from scans at 17 different resolutions. Scanner setting: Color photograph, high-resolution printer output, saved as tiff files. Adjustments: original = no image adjustment; sharpened = image sharpened with Photoshop. See text for parameters.

View larger version (20K): [in a new window]   Fig. 3. Estimated diameter of 0.947 mm wire. Photographed and scanned images were made at 7 different resolutions and two image adjustments. Camera setting: ASA 200, 1/23 sec, f-16, manual focus. Scanner setting: color photograph, high-resolution printer output, saved as tiff files. Adjustments: original = no image modification; sharpened = image sharpened with Photoshop. See text for parameters.

View larger version (22K): [in a new window]   Fig. 4. Camera f-stop analysis of length (a) and diameter (b) of 0.947 mm wire 0.74 m long cut into random length pieces. Camera settings: ASA 200, 1/23 sec., manual focus with a resolution of 23.1 p mm-1. Each image was analyzed both with and without sharpening in Photoshop. Horizontal line represents the 0.947 mm point. Vertical line represents 1 pixel width (0.043 mm).

View larger version (18K): [in a new window]   Fig. 5. Scanner estimation of average length and diameter of 947 µm wire 930.5 mm long with 0 to 40 non-parallel wire crossovers and combinations of 40 crossings with 0 to 3 overlaps (40t to 40t3—an overlap is a parallel touch or crossover) and up to two crossovers at an overlap (x or xx). Scanner setting: 23.7 p mm-1, color photograph, high-resolution printer output, saved as tiff files. Adjustments: original = no image adjustment; sharpened = image sharpened with Photoshop (see text for parameters). Pixel width = 0.042 mm.

View larger version (26K): [in a new window]   Fig. 6. Length by diameter class (LD) curves for four wire diameters and a mixture of the four. Scanned at 23.7 p mm-1—same data set as Fig. 2, sharpened. Scanner setting: Color photograph, high-resolution printer output, saved as tiff files. Diameter class size set to 0.042 mm.

View larger version (18K): [in a new window]   Fig. 7. Log scale plots of root length by measured diameter class (LD plot). Switchgrass photographed at 19.2 p mm-1 with the diameter class size set at 0.052 mm; Pasture photographed at 14.3 p mm-1, with diameter class size set tot 0.070 mm. Camera settings: ASA200, 1/23 sec, f-13, manual focus.