Thermal imaging

Thermal imaging is the picture-making step: an infrared camera receives infrared radiation from many points in its field of view and turns those measurements into pixels. The picture may show apparent temperature, radiation intensity, or a colour palette derived from either quantity. It does not directly photograph heat inside the joint. It describes radiation reaching the detector from the visible surface.

That limitation matters around a weld. Surface emissivity, reflected radiation, viewing geometry and the selected camera range all affect what the pixels mean. A bright region is therefore not automatically an accurately measured temperature. The definitions in ISO 10878, the infrared-thermography vocabulary standard, separate the infrared image from the technique used to acquire and interpret it.

Worked distinction: thermal imaging and thermography

Consider a robot-cell camera streaming a colour image of each weld. An operator uses the moving hot region to confirm that the torch remains centred and saves one frame with the job record. That is thermal imaging: radiation has been converted into a spatial picture.

Now suppose the same team documents the surface condition, compensates for emissivity and reflected radiation, extracts a cooling curve from a fixed region, and interprets the thermal gradient against a validated reference weld. That complete measurement and interpretation activity is thermography. Thermal imaging supplies the image; thermography is the disciplined method applied to it. Neither label proves a subsurface imperfection or an acceptance result by itself.

For welding work, this distinction prevents a saved colour frame from being described as a temperature measurement without the supporting conditions. It also keeps process observation separate from post-weld NDT: the image can reveal a repeatable anomaly worth investigating, while the governing inspection plan decides how the finished joint is examined and accepted.