# Find object size on photo



## balancin (Nov 29, 2011)

Hello,

I have one photo with EXIF properties and I need find the size of object in front on camera. How I find de object size ? 
In exif I can find aperture, focal length etc.

Thanks


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## Josh66 (Nov 29, 2011)

Does the exif list the distance the lens was focused to (depending on the camera/lens, that may or may not be in there)?

It you knew the distance, and the angle of view, figuring out the size would just be a math problem.

Is there anything near it of a known size?


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## Josh66 (Nov 29, 2011)

Assuming that you knew the focus distance, and the object in question was the object being focused on - You would have to know the angle of the field of view (which you would know, knowing which lens was used - the exif may even tell you the angle)

Once you knew that, you would have to figure out how much of that the object is taking up.

Knowing that, you could draw an isosceles triangle.  You would know the angle of all three corners, and how tall it was.  From that, you could draw a right triangle knowing one side and all angles.  Knowing that, you could figure out the length of the other two sides.

The length of the short side, times 2, would be the width of your object.


edit
You need one dimension to start.  That could be the camera-to-subject distance, the dimensions of another object near the object in question, etc...  Knowing the angle of the field of view, you could possibly figure out how far away the camera was, depending on what else is in the frame.

All of that is assuming that the photo is not cropped, BTW.


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## Patrice (Nov 29, 2011)

That exercise is the object of photogrammetry. As others have pointed out, either you know the real size of another object at the same distance from the camera in the photo and then determine the scale, or you know the geometry of the camera parameters.


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## table1349 (Nov 30, 2011)

For forensic photography we generally use one of these in the photo.  Makes it real simple. 





If you really need to know then here you go. Geodetic Systems, Inc

Have fun.


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