Proportion distortion in 4 projections: data

Started Feb 16, 2013 | Discussions thread
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John Paul
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Proportion distortion in 4 projections: data
Feb 16, 2013

I almost titled this post, “Projections and marital harmony.” The issue is that the standard rectilinear projection produced by wide angle lenses makes people on the edges look fat. Not the best way to have a happy wife! I remember this effect all the way back to my 35mm lens on my 35mm film camera. Now that I have some ultra-wide lenses, it is even worse. Thanks to a recent thread over on the Micro Four Thirds forum, I downloaded Hugin and started playing around with the Panini projection. But then I started thinking people looked overly tall and skinny. So I tried to produce some empirical data.

Procedure: I used my 9-18mm FT lens on my OMD E-M5 (18-36mm equivalent) and took pics with a basketball in the center, side and corner. I did this at both 9mm and 18mm. Then I used Hugin to change the projection to cylindrical, equirectangular, and Panini. All I did with the controls was in the Fast Panorama Preview to change the projection and click “Fit”. (Especially with Panini, you need to click Fit or you get a blank result.) Then I used Photoshop to measure the height and width of the ball, and calculate the ratio of the two.

Theory: My thinking behind this is that my current concern is the width/height ratio of people in my pics. A.k.a. do they look fat? That may be the most critical parameter to optimize. Given that some kind of distortion is inevitable, it makes sense to try for the tradeoff best for my purpose. My old memories say this may mean that I want a “conformal” projection.

Data:

http://barkmanart.smugmug.com/photos/i-r4tjxvs/0/M/i-r4tjxvs-M.jpg

http://barkmanart.smugmug.com/photos/i-jLQVhcb/0/M/i-jLQVhcb-M.jpg

Discussion:

I notice that the rectilinear projection of the lens has the greatest distortion at the edge, rather than the corner.

Panini does make people look skinny as you get away from the center line, much more so than the other projections,

At 18mm (36mm) Cylindrical looks best.

At 9mm (18mm) the choice seems to be between making people in the corner look skinny (cylindrical) or fat (equirectangular). Wanna guess which I am going to pick?

So for now, I will probably make the cylindrical projection my default when there are people in the pic. But I am aware of two things: 1) I am just starting with this change-the-projection stuff, and 2) whether a projection is conformal is only one aspect of what makes for a pleasing result.

What kind of experience do you all have at getting pleasing pictures of people off the center of the image?

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John Paul -- changing the subject line makes threads easier to follow -- http://barkmanart.smugmug.com

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