How to extact boot.img?

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http://unix.stackexchange.com – I am trying to see the content in the .img files. I googled and got http://javigon.com/category/development-tools/ this website to extract system.img. But it couldn't work for boot.img. When trying to do this for boot.img, it is showing the following: Invalid sparse file format at header magi Failed to read sparse file I want clarification that whether simg2img is used only for extracting system.img? 1.If so, Is there any other method to extract boot.img? 2.If not, what is the problem for not extracting boot.img? Please anyone solve my issue. Thank u in advance. (HowTos)