基于数码相片Gamma校正的水稻叶面积指数估算  

Estimation of paddy rice leaf area index based on photo gamma correction

作　　者：孙涛[1,2] 刘振波[1,2] 葛云健[1,2] 顾祝军[3] 

机构地区：[1]南京信息工程大学,气象灾害省部共建教育部重点实验室,南京210044 [2]南京信息工程大学,遥感学院,南京210044 [3]南京晓庄学院,生物化工与环境工程学院,南京211171

出　　处：《生态学报》2014年第13期3548-3557,共10页Acta Ecologica Sinica

基　　金：国家重点基础研究发展计划(2010CB950701);国家自然科学基金(41071281);江苏省高校优势学科建设工程资助项目

摘　　要：随着数码相机的日益普及,利用数码相机进行作物叶面积指数(LAI)测量不断得以应用。由于数码相机成像时会对入射光辐射强度进行Gamma编码变换,输出的相片DN(Digital Number)值与入射光辐射强度呈非线性关系,会造成在确定相片中植被叶片与背景的分割阈值时出现误差,并最终导致LAI估算存在较大不确定性。以水稻为研究对象,获取不同生长期水稻冠层相片并结合同步LAI 2000测量的LAI数据,基于相片Gamma校正原理,对水稻不同生长期冠层相片进行Gamma校正,在此基础上利用冠层孔隙率方法,估算不同生长期水稻LAI。结果表明,经过Gamma校正相片估算的水稻LAI总体精度有显著提高,相片估算的IMAGE LAI与LAI-2000测量值比较的决定系数达到0.71(P<0.05)。在整个观测期内,两种方法观测的LAI值在时间变化趋势上表现一致,但在不同生长期内存在差别,在水稻分蘖期和拔节期相片估算的IMAGE LAI要高于LAI-2000测量值,孕穗期到抽穗期期间IMAGE LAI低于LAI-2000测量值,乳熟期到成熟期IMAGE LAI又高于LAI-2000的观测结果。The automatic compensation effect in a digital camera can cause a bias of the digital number（ DN） of the acquired images. This study carried out DN correction using gamma transformation theory combined with a look-up table method. The DN of the acquired image generally bears a nonlinear relationship with the intensity of incident light,which is an inherent characteristic in common commercial digital cameras. The gamma method is a nonlinear operation used to code and decode luminance or tri-stimulus values in video or still image systems. It has been widely used in photography and video productions,but is rarely used in image processing and applications to vegetation parameter determination. The gamma transformation is mainly used to compensate for the properties of human vision by maximizing the use of the bits or bandwidth relative to the perception of light and color. If images are not gamma encoded,they allocate too many bits or too much bandwidth to the darker areas that humans cannot differentiate and too few bits to the brighter areas that humans are sensitive to,and would thus require more bits to maintain the same visual quality. Although the visual quality of RAW image is generally not very appropriate in commercial use,the RAW image is precisely required in the retrieval of vegetation parameters to obtain a better fit with field measurements. Apart from the gamma correction,for the various annual paddy rice conditions we used the vertical gap fraction to obtain the leaf area index（ LAI）,which we named image LAI,andcompared with the field LAI from LAI-2000. The results indicated that the correlation coefficients after the correction procedure were remarkably similar with an R2 of 0. 71（ P0. 05）,better than for the uncorrected retrieved figures. In the tilling and jointing stages,there was a close approximation between the vertical gap fraction derived LAI and field LAI,but in the booting and heading stages the differences become obvious,reaching a maximum of 0. 38. However,in the milkripened

关 键 词：数码相片 GAMMA校正 叶面积指数 

分 类 号：TB852.1[一般工业技术—摄影技术] S511[农业科学—作物学]