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Tektronix provides test and measurement instruments, solutions and services for the computer, semiconductor, military/aerospace, consumer electronics and education industries worldwide.
Distortion which results when all of the frequency components of a signal are not transmitted with the same gain or loss. A departure from “flatness” in the gain/frequency characteristic of a circuit. Refer also to the Frequency Response discussion.
Industry:Software
Since picture monitors have a nonlinear relationship between the input voltage and brightness, the signal must be correspondingly predistorted.
Gamma correction is always done at the source (camera) in television systems: the R, G, and B signals are converted to R 1/g, G 1/g, and B 1/g. Values of about 2.2 are typically used for gamma. Gamma is a transfer characteristic. Display devices have gamma (or at least CRTs do).
If you measure the actual transfer characteristic of a CRT used for either television display or computer display, you will find it obeys a power law relationship: Light = Volts^gamma where gamma is 2.35 plus or minus 0.1. CRTs have values between 2.25 and 2.45.
2.35 is a common value. It is a function of the CRT itself, and has nothing to do with the pictures displayed on it. CRT projectors are different; green tubes are typically 2.2 while red is usually around 2.1 and blue can be as low as 1.7. But there are no direct-view CRTs which have values lower than 2.1. Pictures which are destined for display on CRTs are gamma-corrected which means that a transfer characteristic has been applied in order to try to correct for the CRT gamma. Users of TV cameras have to accept the characteristic supplied by the manufacturer, except for broadcasters who have adjustable camera curves (the video engineers adjust the controls until they like the look of the picture on the studio monitor in their area). Even so, no TV camera uses a true gamma curve; they all use rather flattened curves with a maximum slope near black of between 3 and 5. The higher this slope, the better the colorimetry but the worse the noise performance.
Industry:Software
a) The RGB data is corrected to compensate for the gamma of the display. b) Historically, gamma correction was a precompensation applied to the video signal at the camera to correct for the nonlinearities of the CRT (i.e., power function of the electron gun) and, as such, it was the inverse of the electron gun function. It is now widely used, however, to describe “the total of all transfer function manipulations” (i.e., including the departures from a true power law function), whether inherent or intentionally introduced to act upon the video signal for the purpose of reducing the bandwidth for signal processing, making the image on the final display conform to preconceived artistic objectives, and/or providing noise suppression, or even bit rate reduction. c) The insertion of a nonlinear output-input characteristic for the purpose of changing the system transfer characteristic. As this usage has grown, the IEEE definition correlating gamma to an analytical function becomes optimistic. d) An adjustment factor used to correct an image’s intensity when it is displayed.
Display devices can perform gamma correction but raster images can also be gamma corrected with software prior to display.
Industry:Software
The common magnetic constituent of magnetic tapes in the form of a dispersion of fine acicular particles within the coating.
Industry:Software
A table of constants which functions as a nonlinear amplifier to correct the electron gun drive voltages so that the CRT display appears to be linear. Because the gamma function for each color is different in a typical CRT, different values for each color are usually contained in the gamma table. This processes is called Gamma Correction.
Industry:Software
a) The exponent of that power law that is used to approximate the curve of output magnitude versus input magnitude over the region of interest.
b) Video - The power function of the electro gun in a CRT. It has become customary in video, as in photography, to extend the meaning and to use gamma as a synonym for the complete transfer function regardless of curve shape. Note: In the electronics system, increasing gamma decreases image contrast. c) Imaging Processing and Display – Nonlinear processing is useful in many television systems as a means of bandwidth limiting, and is normally applied at the camera. Given the predominance of CRT displays, the chosen exponent is related to that of the electron gun (typically 2.2 for systems with 525/59.94 scanning, 2.8 for systems with 625/50 scanning, and 2.22 for SMPTE 240M).
Industry:Software
a) The slope of the transfer function: density (log of reciprocal transmission ) vs. log exposure. It is thus the power function correlating transmission to exposure. b) Gamma in the photographic sense was originally applied specifically to the straight-line portion of the transfer function. Only if all of the photographic densities corresponding to light intensities in the scene lie within that straight-line portion of the transfer function is gamma proportional to contrast. It is sometimes loosely used to indicate either an average or a point slope of the transfer function.
Note: In the photographic system, increasing gamma increases image contrast.
Industry:Software
The range of voltages allowed for a video signal, or a component of a video signal. Signal voltages outside of the range (that is exceeding the gamut) may lead to clipping, crosstalk, or other distortions.
Industry:Software
The dimension of the gap measured in the direction perpendicular to the surface of a head.
Industry:Software
