How the surface affects colour perception

When light reflects off an object, an element of the light reflects at an equal but opposite angle. This is known as specularly reflected light and is reflected as if by a mirror. The light that is not specularly reflected but is reflected in many different directions is known as diffuse reflectance.

For objects with glossy surfaces, the specularly reflected light is relatively strong and the diffused light is weaker. On matt surfaces, the specular component is weak and the diffused light is stronger.

People only view diffused light and ignore spectral reflectance. However, when looking at a glossy object, the colour appears different because the mirror-like reflectance from the light source is added to the colour of the object.

So how do we control the quality of colour?

Due to the complex nature of colour, we use measuring methods and equipment that accurately identify the colour that is produced.

A three-dimensional measurement system known as the L*a*b* colour space, developed by the Commission Internationale de l’Eclairage (CIE) and measured using a spectrophotometer, enables colour to be identified numerically and subsequently, be communicated accurately regardless of lighting conditions or other environmental factors.

The mnemonic Lab uses L* to represent lightness while a* represents the red to green axis and b* the yellow to blue axis.

The L*a*b* colour space includes all perceivable colours which means that its gamut exceeds those of the RGB and CMYK colour models. One of the most important attributes of the L*a*b* model is its device independency which means that colours are defined independent of their nature of creation, where they are viewed or the device they are displayed on.