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SAA4990H Datasheet(PDF) 9 Page - NXP Semiconductors |
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SAA4990H Datasheet(HTML) 9 Page - NXP Semiconductors |
9 / 28 page 1996 Oct 25 9 Philips Semiconductors Preliminary specification Progressive scan-Zoom and Noise reduction IC (PROZONIC) 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. Fig.6 Noise reduction scheme. (1) Yout =YA × k+YB × (1 − k). (2) see Table 9. (3) see Fig.11. handbook, full pagewidth MGE029 FIELD MEMORY TF2 TF1 FILTER LIMITER FILTER MULTIPLIER (2) k-CURVE (3) Yout (1) YA YB k |
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