An absolute frame difference reports changed values. Lighting variation or another image change can also produce that difference.
Define the difference quantity
An absolute image difference takes corresponding sample differences and removes their sign. It retains the magnitude of value change under the chosen alignment. That quantity does not by itself classify the physical cause, distinguish a newly present object or prove that corresponding scene positions were correctly registered. Primary reference: MathWorks pointwise absolute image difference.
For an original worksheet, preserve both frames and the coordinate correspondence used for subtraction. Keep absolute difference separate from a later decision rule. Losing the sign also removes whether each value increased or decreased, so retain the originals when that distinction matters.
Change fictional brightness without movement
Take invented stationary scene samples [10,20,30]. Define the next frame as [20,30,40] because every value receives a ten-unit offset, with coordinates unchanged. The absolute difference is [10,10,10]. All three positions changed despite the expressly stationary scene.
A second construction with samples [10,30,30] would give [0,10,0] relative to the original. These arrays demonstrate spatially different value changes, not an object detector or a confirmed illumination diagnosis. No numerical difference threshold here establishes physical arrival or defect presence.
Review the cause separately
Prepare an original record of frame identity, alignment, signed changes and absolute changes. If the task concerns object presence, retain the additional evidence and interpretation used to reach that conclusion. A changed pixel is an observation under the image representation, not the complete physical cause.
This guide claims no HM frame-comparison performance. Its reader decision is whether a difference map has been reported as change evidence or promoted into an unsupported object classification. Keep the acquisition conditions and actual task evaluation beside any later threshold applied to that map.
Customer Questions
What is the uniform-offset fictional difference?
[10,10,10].
Does the construction require object movement?
No. Its coordinates are expressly unchanged.
Does absolute difference retain increase versus decrease?
No. Its magnitude removes the sign.
Primary References
These references support the technical principles discussed in this guide. The worked examples and review questions are educational.
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