A succession of ﬂashed still pictures, captured and displayed at a sufficiently high rate, can create the illusion of motion. The quality of the motion portrayal depends on many factors.
Most displays for moving images involve a period of time when the reproduced image is absent from the display, that is, a fraction of the frame time during which the display is black.
In order to avoid objectionable ﬂicker, it is necessary to ﬂash the image at a rate higher than the rate necessary to portray motion.
Refresh rate is highly dependent on the ambient illumination in the viewing environment: The brighter the environment, the higher the ﬂash rate must be in order to avoid ﬂicker.
Refresh rate is generally engineered into a system. Once chosen, it cannot easily be changed. Different applications have adopted different refresh rates, depending on the image quality requirements and viewing conditions of the application.
In the darkness of a cinema, a ﬂash rate of 48 Hz is adequate. In the early days of motion pictures, a frame rate of 48 Hz was thought to involve excessive expenditure for ﬁlm stock, and 24 frames per second were found to be sufﬁcient to portray motion.
So, a conventional ﬁlm projector ﬂashes each frame twice. Higher realism can be obtained with specialized cameras and projectors that operate at higher frame rates, up to 60 frames per second or more.
In a dim viewing environment typical of television viewing, such as a living room, a ﬂash rate of 60 Hz is sufﬁcient.
In a bright environment such as an ofﬁce, a refresh rate above 70 Hz might be required.
|Viewing Environment||Ambient Information||Refresh (flash) rate, Hz||Flash Hz|
|Office||Bright||Many eg: 66, 72,76,85||Same as refresh rate|