Calculate the physical object size in m knowing its distance ,focal length and pixel size in image

问题

I am programming a code in python that compare the detected object size in the image in pixels with its actual physical dimensions from different distances in a way that I know the focal length, distance and digital sensor of the camera.

I am looking for a solution which gives me the physical dimension if I give the object size in pixel in the captured image, then know the distance to the camera and focal length. Then I would like to compare that calculate physical dimension with the actual real object dimension. For example, I know that the real width of the object is 20cm, real height is 40 cm, the distance is 1.1 m, and the focal length is 8mm. My object detection OpenCV code gives me object height is 285 pixels, width is 132 pixels.

I assume the object is parallel to the camera so it is considered as a 2D object.

here is the python code

    actual_H =0.4 #meter
    actual_W =0.2#meter

    F =0.008 #meter_focal_lenght
    Dist = 1.1 #meter distance  
    height=285 #pixel
    width=132  #pixel

    #do calculation
    pix_H =(Dist*float(height))/F
    pix_W =(Dist*float(width))/F
    print feature +"******************"
    print "Pixel Dimension :"+str(float(height))+":"+str(float(width))
    print "Physical Dimension:"+str(pix_H)+":"+str(pix_W)


   #comparision actual and pix
    if (  (pix_H <= actual_H) and (pix_W <= actual_W)):
        return True
    else:
        return False

This calculation is wrong. But dont know where is the problem. Im using this Formula

object size in image = focal length * object size / object distance

Any help?

来源：https://stackoverflow.com/questions/43844117/calculate-the-physical-object-size-in-m-knowing-its-distance-focal-length-and-p