Equation to stretch equirectangular photos

[MaximusNZ]

This is a long shot, but I’ve really no idea where to begin, but it seems do-able?

I am looking for an equation that makes equirectangular images look like a panorama.

A friend showed me a Photoshop plug in that could transform an equirectangular image to Mercator projection. And if I trim the top and bottom off it’s a great way to create panoramas of people.
I’ve added some examples below. First I double the image height, then apply some form of equation, that stretches more as it goes out from the center.

Its not a simple doubling of size, it needs to have a slow growth from the middle put to look “normal” again.

Sorry to just ask out of the blue, but I’ve had a look at equation examples on these forums, and then googled maths equations and can’t even figure out where to start!

 

 

Edited April 30, 2020 by MaximusNZ

[carl123]

I would start here

y+(150*a)*sin(360*y/h) 

The Parameter A Slider controls the effect

But you will probably need to tweak a few things either in the Equation or before/after applying it

 

[mark-h]

That equation is really handy, thanks! Not being great at maths myself, does anyone know what would the equation be if I wanted the opposite effect (i.e. Mercator to equirectangular) as in the original post?