Geometric remapping can leave output locations without valid source coverage. An undistorted image's rectangular size does not resolve that support.
Keep validity with the remapped view
Undistortion remaps image coordinates using a lens model. Output-view choices can retain a full extent, match a chosen image size or crop to valid pixels. The output rectangle therefore needs its valid-source support recorded before every displayed position is treated as an observation of the scene. Primary reference: MathWorks undistorted output views and valid pixels.
For an original worksheet, retain the source image, remapping definition and validity region. Distinguish an assigned border value from an acquired dark pixel. A uniform-looking border in the corrected view does not, by itself, show that the photographed surface had that intensity.
Mark fictional invalid locations
Suppose an invented corrected output has a five-by-five rectangle but only its central three-by-three region maps to valid source samples. That construction contains 25 output positions and nine valid positions, leaving 16 without defined observed-source coverage. It is a hypothetical support mask, not a function-default prediction.
A mean or feature count over all 25 assigned output values would use a different support from a calculation restricted to the nine valid positions. The difference needs to be labeled. It does not establish that the actual camera lost sixteen physical features or that its correction is defective.
Review later calculations on that support
Prepare an original validity overlay and preserve it with any later processing region. If the output is cropped, retain the changed coordinate origin or mapping needed to locate the remaining pixels. Keep source validity separate from the semantic foreground mask used for the inspection question.
This guide claims no HM undistortion model or valid field size. Its reader decision is whether a corrected-image border contains observed data under the declared mapping. Output dimensions alone should not supply that conclusion when a downstream calculation assumes a fully observed neighborhood.
Customer Questions
How many positions are valid in the fictional output?
Nine.
How many lie outside that stated valid support?
Sixteen.
Is an assigned dark border necessarily observed darkness?
No. Source validity must be checked.
Primary References
These references support the technical principles discussed in this guide. The worked examples and review questions are educational.
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