Mura: The Japanese word for blemish has been widely adopted by the display industry to describe almost all irregular luminosity variation defects in liquid crystal displays.
Mura defects are caused by process flaws usually related to cell assembly, which affect the transmission of light through the display.
The cyclical nature, randomness, and often, low contrast of mura makes accurate detection and classification extremely difficult for LCD manufacturers.
Although this is a typical behaviour for AMOLED displays, the pwmfree kernel might increase the visibility of those mura defects due to the reduced pixel current on lower brightness.
The PWM effect is also used to mask those mura defects, so they become less visible:
Another aspect [of the PWM mechanism] is to provide an organic light emitting display device and a driving method thereof by which a transverse and longitudinal mura defect or irregular luminosity variation defects of a panel due to process flaws, for example, caused by a lack of driving currents of the panel can be prevented.
However, although the smart dimming method according to the teachings of the present invention has the optical characteristics of a 300 cd/m2 luminance step, a mure defect may be generated by a deviation of a pixel current due to a low current for pixel driving at a low luminance/low grayscale, and a dispersion of the optical characteristics, such as color difference (MPCD: Minimum Perceptual Color Difference), color temperature, and grayscale linearity, may increase. Due to the problem associated with the increased dispersion of the optical characteristics at a low luminance, a expressible minimum luminance should be limited to 40 cd/m2. If the minimum luminance set to lower than 40 cd/m2, the optical characteristics deteriorates.