Hi, can some one help me changing the back ground of an extjs column/Line chart from a white background to an image of my choice.

Hers is the sample to quickly generate a column chart....... I am trying to get an image as a back ground in the extraStyle block.... But its not working.....Any ideas or help pls?

var data = [ ['Ext JS',115000],['jQuery',250100],['Prototype',150000],['mootools',75000],['YUI',95000],['Dojo',20000],['Sizzle',15000]
];


var store = new Ext.data.ArrayStore({
fields:[{name:'framework'},{name:'users', type:'float'}]
});

store.loadData(data);

//Charts
var columnChart = new Ext.chart.ColumnChart({
store: store,
xField: 'framework',
yField: 'users',
extraStyle:{
//legend:{display: 'bottom'},
//yAxis: {majorGridLines: {size: 1, color: "#FFFFFF"},titleRotation: 90}
//background: { color: '#FFFFFF', alpha : 0}
background: { image: 'icons/bkg.png' }
}
});



// Panels
var panel1 = new Ext.Panel({
title: 'Column chart example',
items:[columnChart]
, loadMask : true //{msg:"Loading..."}
});


var main = new Ext.Panel({
renderTo: 'frame',
width:500,
defaults: {
height:250,
collapsible: true,
border:false,
titleCollapse: true
},
items: [panel1]
});