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SAA4979H

Sample rate converter with embedded high quality dynamic noise reduction and expansion port

Philips Electronics 

Philips Semiconductors

Sample rate converter with embedded high quality

dynamic noise reduction and expansion port

Product specification

SAA4979H

7.1.4 DYNAMIC NOISE REDUCTION

The main function of the noise reduction is shown in Fig.4.

It is divided into two signal paths for chrominance and

luminance. In principal two operating modes can be used,

the fixed and the adaptive mode. In both modes the

applied frequency range, in which the noise reduction

takes place, can be reduced or not reduced (control input:

unfiltered).

The noise reduction operates field recursive with an

averaging ratio (K factor) between fresh (new) and over

previous fields averaged (old) luminance and chrominance

values. Noise reduction can be activated by forcing the

NREN control bit to HIGH. If NREN is LOW the noise

reduction block is bridged via a data multiplexer.

In the fixed mode, the noise reduction produces a constant

weighted input averaging. Because of smearing effects

this mode should not be used for normal operation except

for K = 1. The fixed mode can be activated separately for

chrominance (control input: chromafix) and luminance

(control input: lumafix).

In the adaptive mode, the averaging ratio is based on the

absolute differences of the inputs of luminance and

chrominance respectively. If the absolute difference is low,

only a small part of the fresh data will be added. In cases

of high difference, much of the fresh data will be taken.

This occurs either in situations of movement or where a

significant vertical contrast is seen. The relationship

between the amount of movement and the K factor values

is defined in a look-up table where the steps can be

programmed (control input: Kstep).

It should be noted that recursion is done over fields, and

that pixel positions between the new and old fields always

have a vertical offset of one line. So averaging is not only

done in the dimension of time but also in the vertical

direction. Therefore averaging vertically on, for example, a

vertical black to white edge would produce a grey result.

The averaging in chrominance can optionally be slaved to

the luminance averaging (control input: Klumatochroma),

in that case chrominance differences are not taken into

account for the K factor setting of the chrominance signal

path.

The noise reduction scheme also decreases the

cross-colour patterns effectively if the adaptive noise

reduction for the averaging in chrominance is slaved to the

luminance averaging (control input: Klumatochroma). The

cross-colour pattern does not produce an increase of the

measured luminance difference, therefore this pattern will

be averaged over many fields.

2002 May 28

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