gistfile1.js

function getRgba (ctx, x, y) {
  var colors = ['r', 'g', 'b', 'a']
    , result = {}
    , data = ctx.getImageData(x, y, 1, 1)
  
  data.forEach(function (c, i) {
    result[colors[i]] = c
  })
  
  return result
}