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Lighting & imaging

Overexposure as a tool

Some defects only become visible when you deliberately drive the image into saturation.

Traditional wisdom says: avoid overexposure. During several substrate evaluations I learned that this is not always true.

A reflective part with low-contrast features
On a bright reflective part, low-contrast features can be separated by deliberately pushing exposure.

The idea

Certain defects only become visible when the image is intentionally driven into saturation. The defect changes brightness differently than the surrounding material, so pushing the exposure separates the two even though a "correct" exposure hides the difference.

Where it helped

  • Conductive-substrate inspection where defects and background were nearly identical at normal exposure.
  • Ceramic substrate evaluations with subtle surface differences.

The takeaway

Exposure is not just about getting a pretty picture. It is a contrast control. Sometimes the "wrong" exposure is the one that makes the defect obvious.