I like watching “Border Security” (a program about our CBSA [customs & immigration] folks) on TV, and am curious about the X-Ray unit used to X-Ray mailed parcels. The screen shows colours, and some of the comments by the inspectors seems to imply the colours are important (“looks like something organic there…”). What are they using that would distinguish different substances on an X-Ray?
The color of the image is artificial; the image is processed by an expert software system that assigns different colors to different classes of materials, based on the material density. The material density is determined by a two-layer photodiode array detector. The layers of diodes are separated by a sheet of metal. The metal absorbs “soft” X-rays, letting the shorter-wavelength, more penetrating “hard” X-rays through to the bottom layer, turning the detector into a crude two-band spectrometer.
Thanks. Interesting!
Two frequencies of Xray are two colours of xray.
The combinations of the two colours can be mapped to any number of visual colours.