ADV7182ABCPZ datasheet(36/102 Pages) AD

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ADV7182A

Data Sheet

Rev. 0 | Page 36 of 102

CKILLTHR[2:0], Color Kill Threshold—Address 0x3D,

Bits[6:4]

The CKILLTHR[2:0] bits allow the user to select a threshold for

the color kill function. The threshold applies only to QAM-based

(NTSC and PAL) or FM-modulated (SECAM) video standards.

To enable the color kill function, the CKE bit must be set. For

the 000, 001, 010, and 011 settings, chroma demodulation

inside the ADV7182A may not work satisfactorily for poor

input video signals.

Table 49. CKILLTHR Function

Description

CKILLTHR[2:0]

NTSC, PAL

SECAM

000

Kill at <0.5%

No color kill

001

Kill at <1.5%

Kill at <5%

010 (default)

Kill at <2.5%

Kill at <7%

011

Kill at <4%

Kill at <8%

100

Kill at <8.5%

Kill at <9.5%

101

Kill at <16%

Kill at <15%

110

Kill at <32%

111

Reserved for Analog

Devices internal use

only; do not select

Reserved for Analog

Devices internal use

only; do not select

CHROMA TRANSIENT IMPROVEMENT (CTI)

The signal bandwidth allocated for chroma is typically much

smaller than that for luminance. In the past, this was a valid way

to fit a color video signal into a given overall bandwidth because

the human eye is less sensitive to chrominance than to luminance.

The uneven bandwidth, however, may lead to visual artifacts in

sharp color transitions. At the border of two bars of color, both

components (luma and chroma) change at the same time (see

Figure 26). Due to the higher bandwidth, the signal transition

of the luma component is usually much sharper than that of the

chroma component. The color edge is not sharp, and in the

worst case it can be blurred over several pixels.

Figure 26. CTI Luma/Chroma Transition

The chroma transient improvement block examines the input video

data. It detects transitions of chroma and can be programmed to

create steeper 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 was taken to ensure that edge ringing and undesirable

saturation or hue distortion are avoided.

Chroma transient improvements are needed primarily for signals

that have severe chroma bandwidth limitations. For these types

of signals, it is strongly recommended to enable the CTI block

via CTI_EN.

CTI_EN, Chroma Transient Improvement (CTI) Enable—

Address 0x4D, Bit 0

Set CTI_EN to 0 to disable the CTI block.

Set CTI_EN to 1 (default) to enable the CTI block.

CTI_AB_EN, Chroma Transient Improvement Alpha

Blend Enable—Address 0x4D, Bit 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.

Set CTI_AB_EN to 0 to disable the CTI alpha blender.

Set CTI_AB_EN to 1 (default) to enable the CTI alpha-blend

mixing function.

CTI_AB[1:0], Chroma Transient Improvement Alpha

Blend—Address 0x4D, Bits[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;

however, it may also increase the visual impact of small amplitude,

high frequency chroma noise.

Table 50. CTI_AB Function

CTI_AB[1:0]

Description

Sharpest mixing between sharpened and

original chroma signal

Sharp mixing

Smooth mixing

11 (default)

Smoothest mixing between sharpened and

original chroma signal

CTI_C_TH[7:0], CTI Chroma Threshold—Address 0x4E,

Bits[7:0]

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

how big the amplitude step in a chroma transition must be if it

is going 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.

LUMA SIGNAL

DEMODULATED

CHROMA SIGNAL

LUMA SIGNAL WITH A

TRANSITION, ACCOMPANIED

BY A CHROMA TRANSITION

ORIGINAL, SLOW CHROMA

TRANSITION PRIOR TO CTI

SHARPENED CHROMA

TRANSITION AT THE

OUTPUT OF CTI

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