SAA4990H View Datasheet(PDF) - Philips Electronics

Part Name

Description

Manufacturer

SAA4990H

Progressive scan-Zoom and Noise reduction IC (PROZONIC)

Philips Electronics 

Philips Semiconductors

Progressive scan-Zoom and Noise

reduction IC (PROZONIC)

Preliminary specification

SAA4990H

Noise and cross-colour reduction

The noise reduction is field recursive with an average ratio

between fresh and over previous fields averaged

luminance and chrominance.

Two operating modes can be used in principal: the fixed

and the adaptive mode (see Table 6).

In the fixed mode, the averaging produces a constant

linear combination of the inputs. Except for k = 1, the fixed

mode should not be used for normal operation, because of

its smearing effects.

In the adaptive mode, the averaging ratio switches softly

on the basis of absolute differences in luminance among

the inputs. When the absolute difference is low, only a

small part of the fresh data will be added. When the

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

This occurs in either the situation of movement or where a

significant vertical contrast is seen.

To latter remark, note that recursion is done over a field,

and the pixel positions one field apart always have a

vertical offset of one frame line. So averaging is not only

done in the dimension of time but also in the vertical

direction. Therefore averaging vertically on e.g. a vertical

black to white edge would provide a grey result if this was

not adapted for.

The averaging in chrominance is slaved to the luminance

averaging. This implies that differences in the

chrominance are not taken into account for the k-factor

setting.

The noise reduction scheme effectively decreases both

noise and cross-colour patterns.

The cross-colour pattern does not produce an increase of

the measured luminance difference, therefore this pattern

will be averaged over many fields.

handbook, full pagewidth

YA

k

FIELD

YB

MEMORY

Yout

(1)

(1) Yout = YA × k + YB × (1 − k).

(2) see Table 9.

(3) see Fig.11.

TF1

FILTER

LIMITER

TF2

FILTER

MULTIPLIER

(2)

k-CURVE

(3)

MGE029

Fig.6 Noise reduction scheme.

1996 Oct 25

9

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