Mask out pixels smaller than 1ha in Google Earth Engine

Question

I am new here so please forgive any mistakes in this post: I have a simple script to classify cultivated area vs none cultivated areas using Sentinel-2 in GEE. I want to mask out all objects that are less than 1 ha in size. Below is the script I have put together, but the problem I have is that the .connectedComponents and .connectedPixelCount have a maxSize of 255, which drops very large chunks of the cultivated area's when I finally apply the mask in the end. Can anyone help me tidy this up?

//Add Sentinel imagery from Dry Season 2019, layer stack, composite and clip
var Sentinel2 = ee.ImageCollection('COPERNICUS/S2_SR')
                  .filterDate('2019-03-20', '2019-08-31')
                  .filter(ee.Filter.lt('CLOUDY_PIXEL_PERCENTAGE', 10))
                  .filterBounds(AOI)
                  .select(['B2', 'B3','B4','B8','B11','B12'])
                  .median()
                  .clip(AOI);
//Create an NDVI band and add it to the Sentinel stack
var ndvi = Sentinel2.normalizedDifference(["B8","B4"]);
var with_ndvi = Sentinel2.addBands(ndvi);

// Merge the training points to a single FeatureCollection.
var trainingPoints = Cult.merge(NoCult);

//Obtain signatures for each class from the image
var training = with_ndvi.sampleRegions({collection: trainingPoints, properties: ['Class'],  scale: 10});

//Train the classifier
var classifier = ee.Classifier.cart().train(training, 'Class');

//Run the classification
var classified = with_ndvi.classify(classifier);

//Extract out just the agriculture
var agric = classified.updateMask(classified.eq(1));

// Uniquely label the agric areas.
var objectId = agric.connectedComponents({
  connectedness: ee.Kernel.plus(1),
  maxSize: 255
});

// Compute the number of pixels in each object defined by the "labels" band.
var objectSize = objectId.select('labels')
  .connectedPixelCount({
    maxSize: 255, eightConnected: false
  });

// Get a pixel area image.
var pixelArea = ee.Image.pixelArea();

// Multiply pixel area by the number of pixels in an object to calculate the object area. 
var objectArea = objectSize.multiply(pixelArea);

// Mask out objects below 1 hectare
var areaMask = objectArea.gte(10000);

//Create final cultivated area layer with mask applied
var agricFin = agric.updateMask(areaMask);

Map.addLayer(agricFin);
Map.addLayer(agric);

Link to the script is here: https://code.earthengine.google.com/1172c13936c011b39f2c62abf56fecb3

Answer 1

You could maybe do like this:

// Pick large enough maxSize to fit your minArea at the scale you
// want to export in. As you zoom in, you will require more and more
// pixels to get your minArea. At some point it will be larger than
// maxSize, and everything get masked out.
var minArea = 10000
var maxSize = 200
var pixelCount = agric.connectedPixelCount(maxSize)
var minPixelCount = ee.Image(minArea).divide(ee.Image.pixelArea())
var agricFin = agric.updateMask(pixelCount.gte(minPixelCount))

https://code.earthengine.google.com/88e72c3a3c900fffd03e6c0b32e20566