I want to confirm and expand on my understanding of lens distortion models. The wiki covers barrel, pin cushion, and mustache distortions, but not how it relates to division, brown 3, brown 4, ect.. I feel like I have good grasp on what the names and variables mean and will try to explain them as I understand them and just correct me where necessary.
Divison- Just one curve calculated either positive or negative to correct barrel or pincushion distortion. I imagine this is the most common correction and good enough for the human eye unless your taking a picture of a checker board and holding a straight edge up to your monitor.Barrel
Division curve side view
Brown 3- A more accurate estimate of distortion as it can compensate for 3 variables such that if the distortion curve changes moving from the center to the outer edge of the image. With mustache distortion you would need to use this model as the distortion is by definition a combination of barrel and pincushion.
Side view of the multiple distortion curves ( the best I could draw )
Brown 4 - Same just with 4 variables.
Brown 3 and 4 with Tangents - Same thing as before just with the correction now off center to correct for glass misalignment within the lens. Stabilization might introduce these "tangent" shifts as the lens or sensor wiggles around in the camera to correct motion blur from camera movement. Also cheaper/older camera (think camera phones, drones, ect) might benefit the most here. Think of how a CD player lens is focused. Its free floating and is moved by a magnetic field.
Tangent - The mustache distortion is off center either because of misaligned lens glass or camera stabilization
It is important to note that most lens correction software is only is only an estimate. Camera and lens manufactures have a range of acceptable values in variance. Reality Capture can in most cases (with enough pictures) create a more accurate distortion model for each individual picture. I imagine this is a multi-variable equation. You have many variables and the more equations you have the more certain about the variables values you can be.
Please correct. I'm positive I'm wrong I'm many places, as I can only assume (through context clues and such) what these values mean.
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