In the process we hope to also learn something about the cirrus emission itself. For a recent review see Basart et al. A fundamental feature of mathematical morphology is the use of a structuring element. This is essentially a smaller version of the input image, and contains structure of the type that is to be analyzed in the image. The two basic morphological operations are dilation and erosion.
Dilation expands and brightens an image, while erosion shrinks and darkens.
Dilation is performed by sliding the structuring element over the image while adding the values of the structuring element to the image, and then recording the maximum value reached at each point. Erosion is similar, except that the structuring element values are subtracted from the image, and the global minimum is taken. The opening operation is created by first eroding and then dilating an image. Physically, the opening operation extracts all structure brighter than the background whose size is smaller than the structuring element and which conforms to the shape of the structuring element. We first open the image using a truncated Gaussian structuring element that has a FWHM .