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Abstract

Ordinarily, television signals are subjected to gamma correction at the source to compensate for non-linearities in CRT-based displays in accordance with set standards. However, it has been found in practice that all CRT-based displays do not exhibit the same amount of non-linearity. Hence, some television receivers include gamma correction circuitry which compensate for the difference between the particular CRT display and that assumed by the transmission system standard. In addition the above, circuitry is added for adapting this correction to local areas on the display thereby achieving dynamic range equalization. The input video signal is first low-pass filtered and then subjected to a normalization between 0.0 and a first predefined maximum value A. A second predefined value B is then added to this normalized signal generating a gamma exponential. At the same time, the input video signal is normalized for the range 0.0 and 1.0. This normalized input signal is then raised to an exponential power equivalent to the gamma exponential. Finally, this resultant signal is re-scaled back to the dynamic range of the input video signal. The resultant video signal on display then has the dark portions thereof more visible without the bright parts looking washed out.

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