file-header of jpg-grafic?

i know it's probably a little bit off topic, but i didn't know which board fits best for this thread.

my problem: i want to know at which position in the jpg-grafic the bytes for the size of the image (width and height) are stored...

e.g. in a gif-grafic, bytes 7 and 8 store the width, bytes 9 and 10 store the height-information of a gif-images...

but where are these information stored in a jpg-image?

and, if possible and someone knows, where are these informations in png-grafic?


thansk a lot...

try for file-format info here or look at this free jpeg library