Skauli Torbjørn
Norwegian Defence Research Establishment (FFI), Kjeller, Norway.
Opt Express. 2011 Jul 4;19(14):13031-46. doi: 10.1364/OE.19.013031.
Many types of hyperspectral image processing can benefit from knowledge of noise levels in the data, which can be derived from sensor physics. Surprisingly, such information is rarely provided or exploited. Usually, the image data are represented as radiance values, but this representation can lead to suboptimal results, for example in spectral difference metrics. Also, radiance data do not provide an appropriate baseline for calculation of image compression ratios. This paper defines two alternative representations of hyperspectral image data, aiming to make sensor noise accessible to image processing. A "corrected raw data" representation is proportional to the photoelectron count and can be processed like radiance data, while also offering simpler estimation of noise and somewhat more compact storage. A variance-stabilized representation is obtained by square-root transformation of the photodetector signal to make the noise signal-independent and constant across all bands while also reducing data volume by almost a factor 2. Then the data size is comparable to the fundamental information capacity of the sensor, giving a more appropriate measure of uncompressed data size. It is noted that the variance-stabilized representation has parallels in other fields of imaging. The alternative data representations provide an opportunity to reformulate hyperspectral processing algorithms to take actual sensor noise into account.
许多类型的高光谱图像处理都可以从数据中的噪声水平信息中受益，这些信息可从传感器物理特性中得出。令人惊讶的是，此类信息很少被提供或利用。通常，图像数据表示为辐射值，但这种表示可能会导致次优结果，例如在光谱差异度量中。此外，辐射数据不能为计算图像压缩率提供合适的基线。本文定义了高光谱图像数据的两种替代表示形式，旨在使传感器噪声便于图像处理使用。“校正后的原始数据”表示形式与光电子计数成正比，可以像处理辐射数据一样进行处理，同时还能更简单地估计噪声并实现更紧凑的存储。通过对光电探测器信号进行平方根变换获得方差稳定表示形式，以使噪声与信号无关且在所有波段上保持恒定，同时还能将数据量减少近一半。然后，数据大小与传感器的基本信息容量相当，从而为未压缩数据大小提供了更合适的度量。需要注意的是，方差稳定表示形式在其他成像领域也有类似情况。这些替代数据表示形式为重新制定高光谱处理算法以考虑实际传感器噪声提供了机会。
