ADV7180WBSTZ datasheet(39/120 Pages) AD

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Data Sheet

ADV7180

Rev. G | Page 39 of 120

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 29). 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 can be

blurred, in the worst case, over several pixels.

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

Figure 29. 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 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 have 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

Alpha 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 48. 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 specifying

how big the amplitude step in a chroma transition must be to be

steepened by the CTI block. Programming a small value into this

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.

ADV7180WBSTZ Datasheet(PDF) 39 Page - Analog Devices

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