def getAccurateFocalLengths(imageSize, focalLength, sensorSize):
    """
    Parameters: image size x,y (pixels), focalLength (mili meters), sensorSize x,y (meters)
    
    Focal length listed on the image exif is unitless...
    We need focal length in pixels / meters. 
    Therefore, we scale the exif focal length by number of 
    pixels per meter on the actual CCD sensor.
    """
    w_s = sensorSize[0]  # in meters
    h_s = sensorSize[1]
    
    w_i = imageSize[0]  # in pixels
    h_i = imageSize[1]
    
    f = focalLength / 1000.0 # milimeters to meters
    
    focalLengthPixelsPerMeter = (w_i / w_s * f, h_i / h_s * f)
    return focalLengthPixelsPerMeter