Johannesburg skyline 


The digital camera, colour perception and light

A work in progress

The digital age has brought us ever cheaper and more wonderful cameras. Now just about everyone can own an advanced digital camera with more features than we know what to do with.

At the same time we now have new methods of lighting: A range of compact fluorescent lamps (CFLs), which have much lower heat dissipation than incandescent lamps, light-emitting diodes (LEDs) of various kinds, and probably more to come.

However, these newer lamps do not produce a continuous spectrum of light, such as we get from the sun or from incandescent lamps.  Instead, they produce light at very sharply defined wavelengths, and it is only by judiciously combining the various wavelengths available that we get light which approximates our "normal" daylight or white light.  We can trick the human eye into thinking that the spectrum is continuous, but as we will see that is not true and there are some interesting consequences.

At the same time, the modern digital camera also performs some interesting tricks in order to capture colour. The most common scheme is to detect the colours in a scene by means of three sets of sensors, corresponding to three primary colours: red, green and blue.  If we then reproduce the scene using these three colours, again we trick the human eye into perceiving colour... but we are not actually seeing the original colours in the scene.  Sounds complicated?

Let's look at the whole sequence, where we use a new artificial light to illuminate a scene, capture the scene with a digital camera, and then display it on a pc screen:

Original scene Reflects all wavelengths of light
Illuminate with CFL lamp Reflects only certain specific wavelengths
Observe with human eye

Eye/brain trick #1

Capture with digital camera Capture specific wavelengths into 3 categories: red, green, blue
Display image on CRT / flat screen Display in RGB - Eye/brain trick #2

These pages are an exploration of the above themes.  It will be interesting, and may even provide some useful insights.

Next: The visible spectrum