ADV7181BBCPZ datasheet(33/96 Pages) AD

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ADV7181B

Rev. 0 | Page 33 of 96

The chroma transient improvement block examines the input

video data. It detects transitions of chroma, and can be

programmed to “steepen” the chroma edges in an attempt to

artificially restore lost color bandwidth. The CTI block,

however, operates only on edges above a certain threshold to

ensure that noise is not emphasized. Care has also been taken to

ensure that edge ringing and undesirable saturation or hue

distortion are avoided.

Chroma transient improvements are needed primarily for

signals that experienced severe chroma bandwidth limitations.

For those types of signals, it is strongly recommended to enable

the CTI block via CTI_EN.

CTI_EN Chroma Transient Improvement Enable,

Address 0x4D [0]

Setting CTI_EN to 0 disables the CTI block.

Setting CTI_EN to 1 (default) enables the CTI block.

CTI_AB_EN Chroma Transient Improvement

lpha Blend Enable, Address 0x4D [1]

The CTI_AB_EN bit enables an alpha-blend function within

the CTI block. If set to 1, the alpha blender mixes the transient

improved chroma with the original signal. The sharpness of the

alpha blending can be configured via the CTI_AB[1:0] bits.

For the alpha blender to be active, the CTI block must be

enabled via the CTI_EN bit.

Setting CTI_AB_EN to 0 disables the CTI alpha blender.

Setting CTI_AB_EN to 1 (default) enables the CTI alpha-blend

mixing function.

CTI_AB[1:0] Chroma Transient Improvement Alpha Blend,

Address 0x4D [3:2]

The CTI_AB[1:0] controls the behavior of alpha blend circuitry

that mixes the sharpened chroma signal with the original one. It

thereby controls the visual impact of CTI on the output data.

For CTI_AB[1:0] to become active, the CTI block must be

enabled via the CTI_EN bit, and the alpha blender must be

switched on via CTI_AB_EN.

Sharp blending maximizes the effect of CTI on the picture, but

may also increase the visual impact of small amplitude, high

frequency chroma noise.

Table 41. CTI_AB Function

CTI_AB[1:0]

Description

Sharpest mixing between sharpened and original

chroma signal.

Sharp mixing.

Smooth mixing.

11 (default)

Smoothest alpha blend function.

CTI_C_TH[7:0] CTI Chroma Threshold,

Address 0x4E [7:0]

The CTI_C_TH[7:0] value is an unsigned, 8-bit number speci-

fying how big the amplitude step in a chroma transition has to

be in order to be steepened by the CTI block. Programming a

small value into this register causes even smaller edges to be

steepened by the CTI block. Making CTI_C_TH[7:0] a large

value causes the block to improve large transitions only.

The default value for CTI_C_TH[7:0] is 0x08, indicating the

threshold for the chroma edges prior to CTI.

DIGITAL NOISE REDUCTION (DNR)

Digital noise reduction is based on the assumption that high

frequency signals with low amplitude are probably noise and

that their removal, therefore, improves picture quality.

DNR_EN Digital Noise Reduction Enable,

Address 0x4D [5]

The DNR_EN bit enables the DNR block or bypasses it.

Setting DNR_EN to 0 bypasses DNR (disables it).

Setting DNR_EN to 1 (default) enables digital noise reduction

on the luma data.

DNR_TH[7:0] DNR Noise Threshold, Address 0x50 [7:0]

The DNR_TH[7:0] value is an unsigned 8-bit number used to

determine the maximum edge that is interpreted as noise and

therefore blanked from the luma data. Programming a large

value into DNR_TH[7:0] causes the DNR block to interpret

even large transients as noise and remove them. The effect on

the video data is, therefore, more visible.

Programming a small value causes only small transients to be

seen as noise and to be removed.

The recommended DNR_TH[7:0] setting for A/V inputs is

0x04, and the recommended DNR_TH[7:0] setting for tuner

inputs is 0x0A.

The default value for DNR_TH[7:0] is 0x08, indicating the

threshold for maximum luma edges to be interpreted as noise.

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