Losing pixels values when counting by value

Question

I have a script that calculates number of pixels with NDVI values that are higher than 0.3, 0.5 and 0.7.

My code runs with no errors, but it get value 0 and doesn't really count.

what can be the reason?

var meanImage=ee.Image(byYear.get[0]);

var gt03 = meanImage.gt(0.3).selfMask().rename('NDVI_gt03');
var gt04 = meanImage.gt(0.5).selfMask().rename('NDVI_gt05');
var gt05 = meanImage.gt(0.7).selfMask().rename('NDVI_gt07');

Map.addLayer(gt03,NDVIcolor,'gt03');
Map.addLayer(gt04,NDVIcolor,'gt05');
Map.addLayer(gt05,NDVIcolor,'gt07');

//count the number of total pixels
var c03 = gt03.reduceRegion({
  reducer: ee.Reducer.count(),
  geometry: geometry,
  crs: 'EPSG:4326',
  scale: 30,
  });

var c05 = gt05.reduceRegion({
  reducer: ee.Reducer.count(),
  geometry:geometry,
  crs: 'EPSG:4326',
  scale: 30,
  });

  var c07 = gt07.reduceRegion({
  reducer: ee.Reducer.count(),
  geometry:geometry,
  crs: 'EPSG:4326',
  scale: 30,
  });
// print the dictionary output
print(c03,'Total Pixels gt 0.3 ');
print(c05,'Total Pixels gt 0.5 ');
print(c07,'Total Pixels gt 0.7 ');

I have tried also to use listOfImages but still got 0.

My end goal is to calculte the number of pixels with the given values for one image.

link for my code: https://code.earthengine.google.com/559d0922b50d67cf01e4d5b03a21666d

Answer 1

If you share your assets we can make sure the issue is the way you select the images:

By year is and object of type imageCollection, .get() won't select images for you. This should work:

var meanImage=ee.Image(byYear.first());
var gt03 = meanImage.gt(0.3).selfMask().rename('NDVI_gt03');
var gt05 = meanImage.gt(0.5).selfMask().rename('NDVI_gt05');
var gt07 = meanImage.gt(0.7).selfMask().rename('NDVI_gt07');
//count the number of total pixels
var c03 = gt03.reduceRegion({
  reducer: ee.Reducer.count(),
  geometry: geometry,
  crs: 'EPSG:4326',
  scale: 30,
  });

var c05 = gt05.reduceRegion({
  reducer: ee.Reducer.count(),
  geometry:geometry,
  crs: 'EPSG:4326',
  scale: 30,
  });

  var c07 = gt07.reduceRegion({
  reducer: ee.Reducer.count(),
  geometry:geometry,
  crs: 'EPSG:4326',
  scale: 30,
  });
// print the dictionary output
print(c03,'Total Pixels gt 0.3 ');
print(c05,'Total Pixels gt 0.5 ');
print(c07,'Total Pixels gt 0.7 ');

If you want to use .get() you'll have to turn the collection into a list first and select the element which you then cast to an ee.Image object.

In theory the 0 can also come from the fact there are no pixels in the ranges you define.

// EDIT

If you want to map over the images and return for each image the pixel count, one way of doing it could be like this:

    var listOfImages =(byYear.toList(byYear.size()));
    print(listOfImages, 'list')

    var stats = listOfImages.map(function(img){
      var image = ee.Image(img).select('NDVI_mean')

      var c03 = image.gt(0.3).selfMask().reduceRegion({
        reducer: ee.Reducer.count(),
        geometry: geometry,
        crs: 'EPSG:4326',
        scale: 30,
      }).values().get(0);

      var c05 = image.gt(0.5).selfMask().reduceRegion({
        reducer: ee.Reducer.count(),
        geometry: geometry,
        crs: 'EPSG:4326',
        scale: 30,
      }).values().get(0);

        var c07 = image.gt(0.7).selfMask().reduceRegion({
        reducer: ee.Reducer.count(),
        geometry: geometry,
        crs: 'EPSG:4326',
        scale: 30,
      }).values().get(0);

      return image.set('c03', c03).set('c05', c05).set('c07', c07)
    })
print(stats)

It is not a very elegant solution, but i'm no sure if this is what you are looking for.