What is telephoto compression (perspective compression)? Tom Axford 2023

Yes, it does change, but not if you are "seeing" it as purely an image that is being shrunk. You have to try to imagine that you are looking at a real scene, not just at a two-dimensional photograph.

It is often easier to imagine that you are looking at a real scene when viewing a moving image. Have a look at the second video in this article. Zooming the lens is the same as shrinking or expanding the image. When the lens is zoomed back to a shorter focal length the image is shrunk. This makes the distances from the camera appear greater, so the train appears to be moving faster.

Most people see the illusion of the train moving faster even if they do not consciously "see" the distances increasing when a still image is shrunk.

Another situation in which the perspective seen by the viewer is particularly important is the rear-vision mirrors (or cameras) in a car. My car has four: one mirror at the top-centre of the windscreen (which gives a normal perspective), two side mirrors (which give wide-angle views) and a rear-view camera for reversing (which gives an ultra-wide-angle view). The wide-angle views make things appear further away than they really are and the driver needs to make allowance for this when reversing.

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When I am looking at a photograph of a real scene, I always imagine that I am looking at the real scene. My brain does all the hard work to interpret the „pictorial depth“; it is some kind of unconscious inference that happens. The pictorial depth cues are so strong for me, that it is nearly impossible to ignore them and to identifiy the picture as that what it really is: bits, bytes and pixels without any depth.

Imaginging that I look at a real scene and not simple „seeing“ it as purely a flat image, my depth perception does not change with a change in relative viewing distance (h.e. shrinking the entire picture and/or increasing the viewing distance to my display).

And I think simplejoy and JACS share my impression.

But maybe your perception has problems with the shrinking process itself. So please try the following: Look at the picture in full screen mode and with your usually viewing distance to the screen, then place yourself farther away, look again at the full screen image and – of course – imagine you are in the scene: Does your depth perception have changed? Do you perceive the koalas now farther away?

You are clearly having difficulty in "seeing through" the 2-D picture to imagine the real scene that the image represents.

I suggest that you try a completely different situation. While driving your car down a busy highway, glance in the side mirror to look at the traffic behind. The side mirror is usually curved to give a wide-angle view. This shrinks the size of the image that you see and makes distances look much greater than they really are (it's not difficult to prove that mathematically). It should be obvious that distances look greater in the wide-angle mirror, although we soon learn to make allowances for these greater distances and not do something likely to cause an accident.

The central rear view mirror usually reflects a normal image with no change of perspective; so we can judge distances nearly as easily in that mirror as we can when looking ahead at the vehicle in front. The difference in perspective between the image seen in the central mirror and the side mirrors should be obvious.

I would not want to be a passenger in a car driven by someone who was unaware of the difference!

Tom, you made an interesting point with the rear-view-mirrors.

This thread is very overloaded with more than 120 posts.

Should I start a new thread to get more feedback? What do you think?

Yes, that seems like a good idea. I think it gets more difficult to look at threads when they get very long.

Hi Tom.

I am preparing a new thread related to the compression effect, but it is very time consuming due to the complexity of the theme and due to the fact that I am not a native English speaker (it’s hard to get all the correct termini technici).

Please could you tell me how I can embed pictures in my text that way, that one can click on it and it then pops of in a new window, like yours of the brick house. I mean, if you click on my koala pics you get not the pic in a new window, instead one get directed to the upload site, that’s annoying.

BTW Yesterday I worked through all the more of 120 posts and replies following your thread which is a brutal tour de force due to the huge amount of information mass.

I came across this post, that unfortunately did not get much regard:

I think this guy is on the right track.

Regards
Mike

I click on the upload file icon (the up-arrow symbol which is second-last in the list of editing icons at the top of the message window. Then click on insert icon next to the name of the image file at the bottom to put a smaller version of the image into the text.