The 3do Company

David R Main

Apparatus and method for use with a sampled input signal having an input sampling frequency F.sub.S. The apparatus including M digital filters, each receiving the input signal, each having a respective transfer characteristic h.sub.m [n] and each producing a respective output signal updated at the input sample rate F.sub.S, each m'th one of the filters updating its output signal in response to a respective m'th phase of the input sample clock, M.gtoreq.2. The apparatus then combines the output signals of the digital filters to produce a combined output signal having a sample rate of at least MF.sub.S. The apparatus may also be viewed as a hybrid digital/analog filter. The method includes steps of receiving the sampled input signal, filtering the sampled input signal through P filters, combining the outputs of the P filters to produce M output signals, 1&lt;M.ltoreq.P, each m'th one of the M output signals being updated in time for respective m'th one of the phase of the input sampling frequency F.sub.S, and combining the M output signals to produce a combined output signal having a sample rate of at least MF.sub.S.

Multi-phase filter/DAC

A digital filter transfer function is implemented using at least two implementing filters, one of which has a transfer function which guarantees an output which is unconditionally within a predefined output compliance range, and the other of which has a transfer function equal to the difference between the overall desired transfer function and the transfer function of the first implementing filter. Typically, the output samples produced by the two implementing filters are summed to provide an overall output sample. However, if the sum of an output sample from one of the implementing filters and the corresponding output sample from the other implementing filter falls either above or below predetermined threshold values, then the output of the first implementing filter, instead of the summed output, is provided as the sample output of the overall filter. Transient undershoots and overshoots are thus prevented, while the response of the filter is degraded only when necessary to avoid compliance range violation.

Amplitude adaptive filter

Gamma correction is performed by dividing the total gamma transfer function input value range into a plurality of segments. The source RGB data is then mapped into an associated x-position in a 'standard' segment, and gamma correction is performed on the mapped value as if it was initially in that standard segment. The resulting corrected value is then de-mapped back into the original input value segment. Only the portion of the gamma correction curve which is within the 'standard' segment is processable by the circuitry. The segments into which the input value range is divided may occupy ratiometrically increasing portions of the input value range, with the high-order half of the range designated as the standard segment. The lowest-order portion may be approximated linearly. Mapping into the standard segment then involves shifting the input value to the left until the highest order logic 1 is in the highest order bit position. A linear approximation of the gamma correction function within the standard segment, possibly with a non-linearity corrector, is then used to determine a gamma-corrected version of each mapped RGB value. These values are then de-mapped back to their original input value segments by multiplying the values by a respective scale factor responsive only to the respective input value segment.

Method and apparatus for gamma correction by mapping, transforming and

A method and apparatus is disclosed for digital multiplication based on sums and differences of finite sets of powers of two. It is observed that for a given multiplicand signal A, multiples of the form A.multidot.P/Q can be defined by adding or subtracting term signals when each term signal (T.sub.i,T.sub.j) is selectively made representative either of the multiplicand (A) multiplied by a power of two (T=A*2.sup.-i) or representative of a nullity (T=0*A). A mapping unit is provided for controlling responsive barrel shifters and for controlling one or more responsive adder/subtractor units so that the resultant system has a transfer function equivalent to that of an n-bits by m-bits multiplier.

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Boulder Creek, CA, United States of America

David R Main