What is False-colour Image

What you see here is a photograph of calcium oxalate taken under high levels of microscopy: 500x magnification at 20.3 x 25.4 centimetres (8 x 10 inches), to be precise. Calcium oxalate crystals make up a large proportion of kidney stones in humans, though they are found elsewhere in nature; for instance, several plants use the needle-like crystals as part of a defence mechanism.

The scanning electron microscope (SEM) that took this image created this level of detail by moving over the kidney stone in a rectangular pattern called a raster scan, with an intensely focused beam of electrons. The electrons struck the surface of the calcium oxalate to produce a range of signals, including secondary electrons, X-rays and visible light. The position of the beam was then married up to the signal that bounced back to the microscope to reproduce that particular part of the stone in an image.

Because the spectral sensitivity of the scanning electron microscope is different to that of the spectrum visible to the human eye, false colour is applied using special software by mapping the spectral bands of the image signal to the red, green and blue equivalents of visible light. It results in the kind of spectacular shot.

False-colour ImageMicrographs (the resulting images captured by an SEM) can reach intense levels of magnification. Not only do they have a much bigger range than light microscopes, but SEMs can actually magnify a specially prepared subject by over 500,000x. The best light microscopes, meanwhile, are restricted to about a 2,000x magnification limit. This allows scanning electron microscopes to view things as tiny as one nanometre – one-billionth of a metre – in width.

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