How to place an image background in a google chart - charts

Question

I need to place a background image in a Google Chart. I've seen solutions which suggest including the chart in a parent div and setting a background image for the parent div. However, if I do that then the background image will also cover the area outside the chart where the axis labels and legend, etc are displayed. I want my image in the chart area itself only.
Alternatively, is there any way to retrieve the chart options so that I could use chartArea.top, chartArea.left, chartArea.width and chartArea.height to overlay an image on the chart in the correct place?
Many thanks, Chris

Answer 1

You can get information about where your chart is drawn in the following manner:
var graph = new google.visualization.LineChart(...);
graph.draw(data, ...);
var boundingBox = graph.getChartLayoutInterface().getChartAreaBoundingBox();
var pixelsFromLeft = boundingBox.left;
You can then use this information to draw a div on the correct position.

Answer 2

Just to contribute to Sjoerd's answer, the full code can look like this:
In Html, as jaime suggested in this stack overflow question:
<div id='brand_div'>
<div id='chart_div'></div>
</div>
In css, as suggested in the same answer:
#brand_div{
background: url(<SOME-URL>) no-repeat;
}
In javascript, using Sjoerd's suggestion:
google.charts.load("current", {packages:["corechart"]});
google.charts.setOnLoadCallback(drawChart);
function drawChart() {
var data = google.visualization.arrayToDataTable([
['ID', 'X', 'Y', 'Temperature'],
['', 80, 167, 120],
['', 79, 136, 130],
['', 78, 184, 50],
['', 72, 278, 230],
['', 81, 200, 210],
['', 72, 170, 100],
['', 68, 477, 80]
]);
var options = {
colorAxis: {colors: ['yellow', 'red']},
width: 450,
height: 300,
title: 'My Daily Activities',
backgroundColor: 'none' // this is important!
};
var chart = new google.visualization.BubbleChart(document.getElementById('chart_div'));
chart.draw(data, options);
// this two lines are the ones that do the magic
var boundingBox = chart.getChartLayoutInterface().getChartAreaBoundingBox();
$('#brand_div').css('background-position', boundingBox.left + "px " + boundingBox.top + "px").css('background-size', boundingBox.width + "px " + boundingBox.height + "px");
}
All this code was also written using the example in google chart's documentation and my answer to this stack overflow question