GEE collection bands from formulas

Question

How could I create a function calculating NDVI difference from actual NDVI and mean NDVI values to add as a new band to the collection?

Something like this:

var ndvi_diff = ndvi.map(function (image) {
  return image.subtract(ndvi_mean).addBands('ndvi_diff');
});

Can I do calculations with different image collections?

Note that I don’t want to reduce the collection into a single image but I would like to have the mean and then the calculated formula for all images in the same collection as new bands.

Answer 1

Similar to this question: Calculating the vegetation condition indices over a stacked vegetation indices in Google Earth Engine

You could try something like this:

var getdiff = function(image){
  var diff = image.subtract(meanImage).rename('ndvi_diff')
  
  return diff // only the vci
}

https://code.earthengine.google.com/9a0d7ac049865ef12eea34e13871cb12