Converting a fisheye image into a panoramic, spherical or perspective projection
Transformations like these have wide applicability. Performing optics in software so to speak, is more flexible and cheaper than grinding lenses and building special cameras.<p>I was charged once, with transforming images for projection onto a sphere through special lenses. I didn't know the lens transform, the manufacturer kept that secret.  I did know that the intensity across the spherical surface was of uniform brightness - the manufacturer boasted about this. With that bound I could guess the transform, as each pixel of the source image would have to illuminate an equal surface area of sphere once projected.<p>The manufacturer advertised a service to do this transform on your image, but they wanted $10K for each run! Once I presented my insights and a little math, they capitulated and did it at cost. I never got to write my projection software in the end.