how to get a camera focal length and dimension of the pixel in mm from intrinsic matrix [closed]

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the focal length in the intrinsic matrix are in mm, i am looking to determinate focal length in pixel in order to extract the pixel dimensions, which i will use to get the width and height in mm for some geometric calculus

I'm shooting a bit from from the hip here, but here but can you tell me a bit more about your application? It sounds like you have a metrology application where you have a camera pointed at something and want to make measurements on (e.g. camera pointed at a table). I think to get pixels to mm you'll need a metric reconstruction which requires some scene information. In the case I mentioned above there's a cheat / approximation you can do.

i did some geometric calculus, to complet my application i am in need to the dimensions of the image in mm