Many artists and observant folks are already well aware that creating an image with a reflection is an art and that it can be very jarring when one is poorly crafted. This is a brief post where I explore specifically what optically is wrong when a reflection is created by mirroring an image.
First we have to understand how real reflections look. Let’s say we have a situation where an observer sees an object that is being reflected by the ground (it’s made of glass, there’s a layer of water, whatever) in Fig A below.
Fig A:
In this case, the observer sees the physical object at one angle and the reflection at a slightly different angle. In Fig B, I’ve updated Fig A to show a 90 degree viewing angle to the physical object and an approximately 45 degree viewing angle to the image. Depending on the shape of the object, this may allow the observer to see more of the “underneath” surfaces in the reflection.
Fig B:
Now, if I am in the process of creating a fake reflection where I’ve simply taken an image of an object and flipped the pixels, the flipped image because it is 2D is at the same viewing angle to the observer as the unflipped image. Since in a real optical setting, the image should appear at a steeper angle, now it appears to be leaned in towards the observer (Fig C).
Fig C:
And an even more fascinating realization is that for such a case to even be physically possible, the reflective surface would have to be bifurcating the angle between the image and its reflection and be perfectly in line with the observer’s eye (Fig D). The fact that this is a physically impossible situation means that seeing such a reflection should feel completely alien and unsettling, especially in a doctored or Photoshopped or drawn image.
Fig D:
Now of course this is an extreme simplification of the situation. Clever artists know that distance matters as well. Shrinking the reflection to accommodate for it’s perceived increased distance helps the reflection feel like it is in the right place. In addition, if the reflective surface has texture and is not completely clear, the observer’s mind will fill in the gaps and think that the image should make sense. Finally, as the distance between the observer and the object increases, the delta between the viewing angles of the object and the reflection becomes a negligible difference anyway.
Nonetheless, I found it to be an interesting thought exercise to explore the physical reality (or non-reality) that may sometimes underlie a gut feeling of a mirrored image being “wrong.”
Albert C Gea 