Earth Engine implements morphological operations as focal operations, specifically
focal_max()
, focal_min()
, focal_median()
, and
focal_mode()
instance methods in the Image
class. (These are
shortcuts for the more general reduceNeighborhood()
, which can input the
pixels in a kernel to any reducer with a numeric output. See
this page for more information on reducing
neighborhoods). The morphological operators are useful for performing operations such
as erosion, dilation, opening and closing. For example, to perform an
opening operation,
use focal_min()
followed by focal_max()
:
// Load a Landsat 8 image, select the NIR band, threshold, display. var image = ee.Image('LANDSAT/LC08/C01/T1_TOA/LC08_044034_20140318') .select(4).gt(0.2); Map.setCenter(-122.1899, 37.5010, 13); Map.addLayer(image, {}, 'NIR threshold'); // Define a kernel. var kernel = ee.Kernel.circle({radius: 1}); // Perform an erosion followed by a dilation, display. var opened = image .focal_min({kernel: kernel, iterations: 2}) .focal_max({kernel: kernel, iterations: 2}); Map.addLayer(opened, {}, 'opened');
Note that in the previous example, a kernel argument is provided to the morphological operator. The pixels covered by non-zero elements of the kernel are used in the computation. The iterations argument indicates how many times to apply the operator.