Image Compression and The Origins Of Life

Human life on Earth is the result of an extremely fortunate environment. This includes our temperate position near a stable star, in a stable area of the galaxy, with neighbouring bodies of the right size and distance to protect us. It is a Rare Earth.

As we evolved, this environment continued (and continues) to influence our ongoing design; not just physiologically, but also technologically.

The Sun emits a wide range of radiation, from very short wavelengths to very long. A star of the Sun’s age and size emits a peak radiation of about 400 to 700 nm, so it’s no surprise that we have evolved to use this particular section of the electromagnetic spectrum for human ‘eyesight’.

Solar Spectrum
(Image used under Creative Commons license from Global Warming Art via Wikipedia)

Once through the Earth’s atmosphere, the Sun’s radiation peaks at roughly 555 nm, which we have handily adapted to detect with the highest sensitivity. This wavelength corresponds to what we interpret as the colour green (the middle of our visible spectrum).

Electronically, we have developed a system to reproduce much of these ‘visible’ wavelengths, called the RGB color model, as commonly used in displays such as televisions and computer monitors. This system does have some limitations, such as the inability to reproduce all of the visible wavelengths, including violet (about 400nm).

The interesting result is that, because our eyes do not have an equal sensitivity across red (R), green (G) and blue (B) – from one end of the spectrum to the other – we can compress these three components individually so that only the most important information is retained with accuracy.

This technique is used by NTSC, the popular television standard used across the Americas, Japan and other countries, to use less bandwidth for non-green colours, as clearly shown in this example.

Read more about this Chroma Subsampling technique on Wikipedia (note that in the article text, the ‘luma‘ component – or brightness – is largely influenced by green).