H - Electricity – 04 – N
Patent
H - Electricity
04
N
350/46, 350/80
H04N 5/202 (2006.01)
Patent
CA 1208769
ABSTRACT: A method of gamma correcting a video signal com- prises the steps of: forming a first signal representative of the logarithm of the logarithm of the video signal; forming a second signal representative of the logarithm of the correction factor, forming a third signal representa- tive of the algebraic sum of the first and second signals; and forming a fourth signal representative of the exponential of the exponential of the third signal, the fourth signal being the gamma corrected signal. A circuit arrangement for performing the method on an input signal Vi applied to an input terminal comprises a first read only memory which stores the function P = logB(-logAVi) where A and B are arbitrary constants, a second read only memory which stores the function Q = logBG where G is the correction factor, an adder which adds the outputs of the read only memories and a further read memory which stores the function A exp [-B exp (R)] where R = P + Q. This enables the usual multi- pliers to be replaced by an adder which is easier to produce in digital form. To perform the inverse gamma correction operation the adder is replaced by a subtractor.
431053
N.v.philips'gloeilampenfabrieken
Van Steinburg C.e.
LandOfFree
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