Why were you still able to see the object when half the lens was covered why was the brightness of the image reduced?

$\begingroup$

What happens to the image of an object kept before a lens if the upper half of lens is covered by an opaque coating?

I understand that the full image will be formed and only the intensity of the image is reduced. But is the intensity uniformly reduced? That is, will the upper and lower half of image have same intensity?

(The object is kept at a distance $1.25f$ before the lens. Half the object is above the principle axis. $f$ is the focal length of lens).