Earth Engine: filtering to non-zero pixels surrounded by only zero value pixels

Question

I'm trying to create a mask of only pixels surrounded by zero-value pixels in the GHSL layer on Google Earth Engine.

The layer image would be: ee.Image('JRC/GHSL/P2016/POP_GPW_GLOBE_V1/2015')

Anyone have advice on how to do this?

Answer 1

You can use connectedPixelCount method:

var i = ee.Image('JRC/GHSL/P2016/POP_GPW_GLOBE_V1/2015')

// Show original
Map.addLayer(i, null, 'POP_GPW_GLOBE_V1')

// Image projection
var proj = i.projection()

// Mask out pixels with values not equal to zero
var mask = i.neq(0)
var masked = i.updateMask(mask).neq(0)

// get pixel's connectedness
var conn = masked.connectedPixelCount(2).reproject(proj)

// Mask where pixels surrounded by zeros have a value of one
var zeros_around = conn.eq(1)

// Show
Map.addLayer(zeros_around, null, 'pixels surrounded by zeros')