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首页> 外文期刊>Botanical Studies >Sky-canopy border length, exposure and thresholding influence accuracy of hemispherical photography for complex plant canopies
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Sky-canopy border length, exposure and thresholding influence accuracy of hemispherical photography for complex plant canopies

机译：复杂植物檐篷半球摄影的天窗边界长度，曝光和阈值影响

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Abstract BackgroundHemispherical photography (HP) is a popular method to estimate canopy structure and understorey light environment, which analyses photographs acquired with wide view-angle lens (i.e. fisheye lens). To increase HP accuracy, the approaches of most previous studies were to increase the preciseness of exposure and thresholding of photographs, while ours quantified effects of canopy properties (gap fraction and length of sky-canopy border (SCB)) and errors of exposure and thresholding on the accuracy of HP.ResultsThrough analysing photographs of real and model canopies, it was showed that HP inaccuracy resulted from the mismatch between exposure and thresholding rather than exposure or thresholding errors alone. HP inaccuracy was a function of the SCB length and the extent of exposure and thresholding errors, but independent of gap fraction.DiscussionIn photographs, SCBs are recorded as grey pixels which greyness is in between that of sky and canopy pixels. When there are exposure and thresholding errors, grey pixels are those prone to be misclassified in image analysis. Longer (vegetation with taller canopies) and wider (lower image sharpness) SCBs in photographs can both result in a higher amount of grey pixels and ultimately higher HP inaccuracy for a given extent of exposure and threshold errors.ConclusionsUsing lenses with view angle narrower rather than that of fisheye lens can shorten the SCB length in photographs and in turn reduce HP estimation inaccuracy for canopy structure and understorey light environment. Since short SCBs and low levels of exposure and thresholding errors can both result in low HP inaccuracy, to identify the true performance of new exposure and thresholding methods for HP, photographs recording canopies with long SCBs and acquired with fisheye lenses should be used. Because HP inaccuracy in a function of the amount of grey pixels resulting from SCBs, the amount of these pixels in photographs can be used as a universal parameter to quantify canopy properties influential to HP estimation and in turn make cross-study comparisons feasible.
机译：摘要BackgroundHemispherical摄影（HP）是一种估算冠层结构和下层光环境的流行方法，其分析了用宽视角镜头（即鱼眼镜头）获得的照片。为了提高HP准确性，最先前研究的方法是提高摄影和拍摄阈值的精确性，而我们的冠层性质的量化效果（间隙分数和天冠层边界（SCB）的长度）和曝光误差和曝光误差和阈值关于HP.Resultsthrough分析真实和模型Canopies照片的准确性，结果表明，HP不准确性由曝光和阈值平衡之间的不匹配而不是暴露或单独阈值误差。 HP不准确性是SCB长度的函数和曝光程度和阈值误差，但与间隙分数无关.Discussionin照片，SCB被记录为天空和顶篷像素之间的灰色像素。当存在曝光和阈值误差时，灰色像素是在图像分析中被错误分类的灰色像素。较长的（植被具有较高的檐篷）和较宽的照片（较低的图像锐度）SCBS均可导致较高量的灰色像素，并且在给定的曝光程度和阈值误差方面最终得到更高的HP不准确性。与视角较窄的镜头，而不是Fisheye镜头的镜头可以缩短照片中的SCB长度，反过来减少了冠层结构和下层光环境的HP估计不准确。由于短的SCB和曝光率低和阈值误差均可导致低HP不准确性，以确定HP的新曝光和阈值处理方法的真实性能，因此使用长SCB的垂直筒读数，并使用鱼眼镜头获取。因为HP在SCB产生的灰色像素的函数中的函数中，所以照片中的这些像素的量可以用作量化对HP估计影响的冠层特性，并且反过来使得交叉研究比较可行。

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