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United States Department of Agriculture

Agricultural Research Service

Title: Sensitivity Analysis of Computer Based Diameter Measurement from Digital Images

item Zobel, Richard

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 20, 2002
Publication Date: March 20, 2003

Interpretive Summary: Nationally and Internationally, soil based constraints to productivity are a significant challenge. In the Appalachian region, crop and pasture productivity is inhibited by many soil based problems. An understanding of root growth and function in pastures of this region will lead to adoption of management strategies that alleviate these difficulties. Current technology does not allow easy estimation of the finest roots, which are also the most important in terms of root function. This paper describes research that demonstrates that an adjustment of digital root images allows current software and technology to accurately measure all sizes of root. These techniques greatly improve our ability to acquire knowledge of root developmental and functional patterns in the Appalachian Region and world- wide.

Technical Abstract: Root diameters less than 0.5 mm are infrequently documented in the literature, yet they are a critical component of the root system. Software capable of measuring root diameters from digital images has been used extensively to measure root length, but little is know of its efficacy in diameter measurements. An Epson 636 scanner with a transparency unit, and a Kodak DCS330, with a 105 mm Macro lens were each used to image sets of random length wires of three diameters, and human hair (1.19 mm, 0.627 mm, 0.229 mm, and 0.057 mm diameter respectively) at a series of pixel sizes (100 - 1200 dpi). Images were analyzed with the MacRHIZO software package either before, or after manipulation with Photoshop. Minimum routine diameter resolution with this system is about 0.05 mm, though the theoretical minimum is 0.01 mm. With un-adjusted images, MacRHIZO pro 3.10b requires a very narrow range of image resolution (200-400 dpi with >1 to 0.5 mm diameter objects), due to measurement errors and psuedo-fine wire/root measurements caused by rough edge effects on the images. The sharpen filter from Adobe Photoshop eliminates the psuedo-fine wire/root effect at all resolutions tested. Images treated with the maximum sharpening from Photoshop have a practical image resolution range of at least 100-2540 dpi. With sharpening, images of mixtures of roots or other objects with diameters between 0.05 and >1 mm can be accurately analyzed with MacRHIZO.

Last Modified: 4/19/2015
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