A camera records the combined effect of illumination, the object, the filter and the detector. Better contrast often starts with choosing which light to measure, rather than simply increasing brightness.
01
Select the information you need
A bandpass filter can favor the inspection illumination while rejecting out-of-band background. Longpass and shortpass designs select broader spectral regions. An IR cut-off filter can reduce infrared contamination of a visible image; an IR transmission filter supports a different sensing objective.
02
Control exposure separately
A neutral density filter reduces intensity over its specified range. It can help avoid saturation, but does not automatically isolate a wavelength or remove surface glare. Anti-reflection coatings reduce unwanted surface reflection; they do not replace a wavelength-selecting filter.
03
For the system integrator
Review illumination bandwidth, detector sensitivity, exposure, filter angle, lens geometry and unwanted spectral regions. Contrast must be checked on representative objects. Avoid assuming that an infrared-transmitting part has the same performance throughout all near- and short-wave infrared wavelengths.
04
A practical example
For PCB inspection, compare images of the target feature and background under candidate illumination bands. Select the band that makes the difference measurable, then define the filter transmission and rejection requirements around it.
Editorial review: 17 September 2026 · Educational principles support product selection; model-specific performance is established by the product data and agreed specification.