Kell factor
The Kellfaktor, also known as K- factor is in the range of raster graphics, and, derived recently in video and television technology, an experimentally determined factor that indicates how much higher a sampled image signal from an image sensor must be minimal in order for image display devices such as a monitor with discrete picture elements ( pixels) Stördarstellung According to minimize a beat. It lies in the range between 0.5 and 1, the value 0.5 corresponds exactly to the sample at the Nyquist frequency ( half the sampling frequency ), the upper limit value of 1 corresponds to the sampling frequency. It is determined by practical experiments and as small as possible to minimize the required number of pixels per unit time in a given bandwidth of the image signal in the discrete system. Theoretically, the signal Kellfaktor describes a type of sub-scanning.
The Kellfaktor is named after Raymond Davis Kell, who led through to the 1930s at Radio Corporation of America (RCA) first experiments and determined an experimental value of 0.64. However, it was not possible Kell going to describe his experimental setup understandable. The later published work of Raymond Kell and his colleagues A. Bedford and G. Fredendall in 1940 comes to a factor of 0.85.
In display units with fixed pixels such as liquid crystal displays ( LCD ), and CCDs as the image pickup device, a comparatively high 0.9 Kellfaktor may be necessary to allow a greater power fault -free representation. Digital High Definition Television (HDTV ) generally works with a Kellfaktor of 0.9. Cathode ray tubes, such as those used in the past in televisions and analog television transmission method, a Kellfaktor of 0.7 is sufficient.
General
A signal sampled with a sampling frequency at least twice as high as the highest spectral components in the signal, according to the Nyquist -Shannon sampling theorem, an error -free reconstruction of the continuous waveform of the discrete individual values is always possible. This case would correspond to a value of 1 or more of the Kellfaktors, but in this case is no reduction in the number of pixels per unit time, and therefore have values of 1 and greater than no significance. The goal is the number of pixels per unit of time necessary to minimize at the same bandwidth, so only values less than 1 are important.
In a Kellfaktor less than 0.5, this corresponds to a sampling frequency which is smaller than the top spectral components in the signal, it comes to the appearance of image frequencies or aliasing that make a correct reconstruction impossible.
In the range of 0.5 to 1, the area where the concrete Kellfaktor can be chosen, come, according to the phase position of the image signal in relation to the phasing of the sampling frequency superposition effects, which manifest themselves as a beat. Depending on the image content and manner of presentation devices these disorders are different. As an example, adjacent picture which consists of alternating white and black vertical lines, so the upper limit frequency corresponds exactly to the sample rate, which is equal to a Kellfaktor of 0.5. The vertical lines in the image are gently sloping downwards to the right of the screen, resulting in different phase angles with respect to the exact vertical sampling points. Due to this tendency, there is a beat that as a mixture, in this case, are the gray areas, of different shapes form. Since these gray areas are not part of the original image content, they act as interference. In a Kellfaktor of 0.66, shown in the second figure, these disturbances are still present, but much weaker. This corresponds to the balance between a reduction in the number of pixels on the one hand and on the other hand, the least possible disturbances.
The image disorders, according to a selected low Kellfaktors are similar to image distortions during the Moiré effect, but that's not to be confused.