Vision
Overview | Understanding vision | Visual functions (5) | Env. context | Design guidance (2) | Pop. stats. (2)
Visual functions
Introduction | Visual acuity | Contrast sensitivity | Colour perception | Usable visual field
Colour can be described by its hue, saturation and brightness (how much light is apparently reflected). Contrast sensitivity is the ability to perceive the difference in brightness between a foreground colour and a background colour. It is related to the size, distance and illumination of the object to be detected. Maximum contrast occurs with white on black or vice versa.
Higher contrast levels result in a greater likelihood of detection by people with low contrast sensitivity. For example, the ability to distinguish number keys from the body of a mobile phone depends on their contrast, the viewing distance, the size of the text and the ambient illumination.
Visual acuity is related to contrast, and low contrast text will be more difficult to discriminate than high contrast text. In addition, controls on products need to be of sufficient contrast against product chassis to be easily detected. Contrast sensitivity is important for activities such as detecting and reading text, moving around in the environment, and detecting the outlines of buildings, roads, and pavements.
The diagrams opposite show some different foreground and background colours for text and the corresponding images viewed with a reduced brightness contrast. Note how a sharp colour distinction helps to discriminate between the foreground and background when the brightness contrast is reduced.
In order to determine which colour combinations are most effective, try viewing this image at various distances from your eyes and squinting as you read it
The same image viewed with reduced brightness contrast.
Overview | Understanding vision | Visual functions (5) | Env. context | Design guidance (2) | Pop. stats. (2)