Setting values for palette in Google Earth Engine

Question

I am very new to GEE. I have been trying to figure out how to assign different colours to different NDVI values. Let's say, in following code, I want to assign 'red' for NDVI value of 0.2-0.4, 'orange' for 0.4-0.6, 'yellow' for 0.6-0.8, and 'green' for 0.8-1. When I use following code, I feel that I do not have full control over the colours that are being assigned to the NDVI values. The colours I get are gradual based on the NDVI value at certain pixel. What I am trying to do is displaying all pixels that fall in the respective NDVI range in the same colour (something that is done in symbology of ArcMap or QGIS). link to the code: https://code.earthengine.google.com/1f92036224ea8e7e193820ca30c1cef7

Code I have:

// Point for filterbound
var roi = ee.Geometry.Point([92.1339935642684,21.19472665398992])

// Center the display to ROI.
 Map.centerObject(roi, 11);
// Function to get NDVI.
var getNDVI = function(image){
  var NDVI = image.normalizedDifference(['B8', 'B4']).rename('NDVI')
  var clouds = image.select('QA60').gte(1024).unmask().not().rename('CloudMask')
  return image.addBands(NDVI).select('NDVI');
  //.addBands(clouds).mask(clouds) 
  };

// Gets the current time.  
var eeNow = ee.Date(Date.now());

// SET OBSERVATION PERIOD
var startDate = '2018-02-15';
var endDate = eeNow;

// Gets image collection of Observation Period
var series = ee.ImageCollection('COPERNICUS/S2').filterDate(startDate, endDate)
          .filterBounds(roi)
          .filter(ee.Filter.lt('CLOUDY_PIXEL_PERCENTAGE', 10))

// APPLY NDVI FUNCTION TO OBSERVATIONS
series = series.map(getNDVI)
 Map.addLayer(series.first(), {bands: ['NDVI'], min:0.2, max: 1, palette: ['red', 'orange', 'yellow', 'green']}, 'first')

Answer 1

I think for this particular job you will need your band values to be intgers from 0 to 4. The most straightforward manner to do so is as follows I guess:

var setPalletes = function(image){
  image = image.select('NDVI');
  var image02 = image.gte(0.2);
  var image04 = image.gte(0.4);
  var image06 = image.gte(0.6);
  var image08 = image.gte(0.8);
  return image02.add(image04).add(image06).add(image08);
};

var newImages = series.map(setPalletes);
Map.addLayer(newImages.first(), {bands: ['NDVI'], min: 0, max: 4, palette: ['black','red', 'orange', 'yellow', 'green']}, 'first');

As you can see, now NDVI values will be above 0.8 so maybe you want to rewrite some values to make it look better. I added black as a color for values below 0.2.

Here is a link to the full code: https://code.earthengine.google.com/05d07373354e0de70684dc7dbb4efab6

Answer 2

One can create user-defined intervals and gradients in color palettes using Google Styled Descriptors. More info here

Answer 3

if you want to apply this range-color palette to one image (from the answer of Kuik) instead of:

var newImages = series.map(setPalletes);

use:

var newImages = setPalletes(yourimage);