Google Chrome Extension to capture whole web page as image

Hi,
We are developing a Google Chrome Extension to capture whole web page as image.

Most of the available Extensions will open a tab/window on the click of a button,where they are showing the

captured web page as image(in new html page).And are telling to right click on the image ,select the option

'save image as' & save it.

e.g.
extension to capture web page-only visible part
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https://chrome.google.com/extensions...npfdcphkbgogdj

extension to capture web page completely
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https://chrome.google.com/extensions...hgiakhnjcddpki


But we want on click of our button to open a 'Savefiledialog' where directly save the present web page as

image. Does anybody have any idea?

Please provide help.

Thanks.