In this resource, the terms brightness and colour brightness have distinct meanings.
- In the first instance, brightness (as opposed to colour brightness) is used to refer to a property of light.
- Colour brightness is used to refer to how much colour something appears to radiate or reflect towards an observer.
- When brightness is used in connection with the HSB colour model it is used alongside hue and saturation and refers to the method of selecting and adjusting colours in software applications such as Adobe Illustrator.
- In this resource, the term brightness is associated with the intensity of light an object such as the Sun or a lightbulb emits.
- The brightness of a light is always determined by comparing it with the brightness of other light sources.
- As light propagates through a vacuum it is invisible but its brightness becomes apparent when a light source shines directly into our eyes or it is reflected towards us.
- The perceived brightness of a light source depends on how the photoreceptive rod and cone cells in the human retina respond to wavelengths of light (rather than the way that translates into the experience of colour).
About colour brightness
- In this resource, the term colour brightness is used to refer to how things appear to a human observer in terms of their perception of colour.
- Colour is what humans see in the presence of radiated or reflected light.
- The brightness of the colour of an object or surface (its colour brightness) depends on the wavelengths and intensity of light that falls on it and the amount it reflects.
- The colour brightness of a transparent or translucent medium may depend on the wavelengths and intensity of light that falls on it and the amount it transmits or reflects.
- Colour brightness often depends on the difference between the way a colour appears to an observer in well-lit conditions compared with its subdued appearance when in shadow or when poorly illuminated.
- The impression of colour brightness is also affected by hue because some hues appear brighter than others to human observers. So a fully saturated yellow may appear relatively brighter than a fully saturated red or blue.
About brightness and colour models
- The term brightness is often used in association with a specific colour model.
- Examples of colour models include:
- The HSB colour model uses the term brightness alongside hue and saturation.
- Some colour models don’t use the term brightness at all, so when we change from one colour model to another it’s best to change our terminology as well.
About the HSB colour model and colour brightness
The HSB colour model is an additive colour model used to mix light. Subtractive colour models are used to mix pigments and inks.
- The only difference between the RGB and HSB colour models is the way colours are represented in terms of colour notation and dealt with in software and apps.
- Both the HSB and RGB colour model deal with how to mix red, green and blue light to produce other colours.
- HSB is popular because it provides an intuitive way to select and adjust colours when using applications such as Adobe Creative Cloud for design, photography or web development.
- The HSB colour model can be used to describe any colour on a TV, computer or phone.
In the HSB colour model:
- Hue refers to the perceived difference between one colour and another and accounts for colour names such as red, yellow, green or blue.
- Hue can be measured as a location on a colour wheel and expressed in degrees between 00 and 2590.
- Saturation refers to the perceived difference between one colour and another in terms of purity.
- Saturation is measured between a fully saturated colour (100%) and an unsaturated colour that appears dull and washed out until all colour disappears leaving only a monochromatic grey tone (0%).
- A fully saturated colour is produced by a single wavelength or a narrow band of wavelengths of light.
- On HSB colour wheels, saturation is usually shown to increase from the centre to the circumference.
- Brightness (colour brightness) refers to the difference between a hue that appears bold and vivid at maximum brightness (100%) and then appears progressively darker in tone until it appears black at minimum brightness(0%).
- Colour brightness is often apparent in the difference between the way a colour appears to an observer in well-lit conditions compared with its subdued appearance when in shadow or when poorly illuminated.