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@ARTICLE{Rose:866522,
      author       = {Rose, Laura and Lobet, Guillaume},
      title        = {{A}ccuracy of image analysis tools for functional root
                      traits: {A} comment on {D}elory et al. (2017)},
      journal      = {Methods in ecology and evolution},
      volume       = {10},
      number       = {5},
      issn         = {2041-210X},
      address      = {Oxford ˜[u.a.]œ},
      publisher    = {Wiley},
      reportid     = {FZJ-2019-05612},
      pages        = {702 - 711},
      year         = {2019},
      abstract     = {Root traits get increasing attention as functional
                      equivalents of above‐ground traits. Image analysis
                      software such as WinRhizo™ and $IJ_Rhizo$ facilitate root
                      trait analyses. Delory et al. (2017) presented a comparison
                      between the accuracy of WinRhizo™ and $IJ_Rhizo$ for
                      measuring root length. We complement their analyses with a
                      comparison of diameter and volume estimates and a comparison
                      of different image resolutions with manual and automatic
                      threshold. We analysed 100 images of fibrous and taproot
                      systems, which were obtained using the root model
                      ArchiSimple. As a result, for each image, diameter, length
                      and volume were known. The images were analysed with
                      WinRhizo™ and $IJ_Rhizo$ and we compared the estimates of
                      diameter, length and volume to ground‐truth values. We
                      further computed relative errors and their magnitude and
                      analysed their dependency on image characteristics and root
                      system properties. At 1,200 and 800 dpi, diameter and length
                      estimates provided by WinRhizo™ and $IJ_Rhizo$ were of
                      comparable accuracy. Diameter errors were balanced. Volume
                      estimates were subjected to a systematic error caused by the
                      assumption of constant diameter. WinRhizo™, however,
                      provides the opportunity to calculate correctly computed
                      volumes from diameter classes. At 1,200 dpi, $IJ_Rhizo$
                      failed to automatically find an appropriate threshold for
                      pixel classification, which fundamentally decreased
                      accuracy. The magnitude of diameter errors increased with
                      root overlap for $IJ_Rhizo.$ The length errors increased
                      with increasing root length, overlap and root length density
                      for WinRhizo™. The magnitude of underestimation of the
                      volume (WinRhizo™) decreased with volume. It was higher
                      for taproot than for fibrous root systems. All errors
                      increased with lower resolution. Our results confirm the
                      results of Delory et al. (2017) regarding the accuracy for
                      length. They further confirm that estimates derived from
                      different software packages or at different resolution
                      should not be compared directly. The characteristics of root
                      systems should be standardized for image analysis. The
                      dependency of errors on the response variable of interest
                      can influence the effect size and increase the probability
                      of errors. Validation of methods should be conducted for
                      each analysed dataset. New image analysis tools should be
                      validated against a real ground‐truth.},
      cin          = {IBG-3},
      ddc          = {570},
      cid          = {I:(DE-Juel1)IBG-3-20101118},
      pnm          = {255 - Terrestrial Systems: From Observation to Prediction
                      (POF3-255)},
      pid          = {G:(DE-HGF)POF3-255},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000471332800010},
      doi          = {10.1111/2041-210X.13156},
      url          = {https://juser.fz-juelich.de/record/866522},
}