ADV7181BBCPZ datasheet(32/96 Pages) AD

32 / 96 page

ADV7181B

Rev. 0 | Page 32 of 96

CG[11:0] Chroma Gain, Address 0x2D [3:0]; Address 0x2E [7:0]

CMG[11:0] Chroma Manual Gain, Address 0x2D [3:0];

Address 0x2E [7:0]

Chroma gain [11:0] is a dual-function register. If written to, a

desired manual chroma gain can be programmed. This gain

becomes active if the CAGC[1:0] mode is switched to manual

fixed gain. Refer to Equation 2 for calculating a desired gain.

If read back, this register returns the current gain value.

Depending on the setting in the CAGC[1:0] bits, this is either:

•

Chroma manual gain value (CAGC[1:0] set to chroma

manual gain mode).

•

Chroma automatic gain value (CAGC[1:0] set to any of the

automatic modes).

Table 39. CG/CMG Function

CG[11:0]/CMG[11:0]

Read/Write

Description

CMG[11:0]

Write

Manual gain for chroma

path.

CG[11:0]

Read

Currently active gain.

()

...

1024

4095

≤

Gain

Chroma

(2)

For example, freezing the automatic gain loop and reading back

the CG[11:0] register results in a value of 0x47A.

Convert the readback value to decimal:

0x47A = 1146d

Apply Equation 2 to convert the readback value:

1146/1024 = 1.12

CKE Color Kill Enable, Address 0x2B [6]

The Color Kill Enable bit allows the optional color kill function

to be switched on or off.

For QAM-based video standards (PAL and NTSC) as well as

FM based systems (SECAM), the threshold for the color kill

decision is selectable via the CKILLTHR[2:0] bits.

If color kill is enabled, and if the color carrier of the incoming

video signal is less than the threshold for 128 consecutive video

lines, color processing is switched off (black and white output).

To switch the color processing back on, another 128 consecutive

lines with a color burst greater than the threshold are required.

The color kill option only works for input signals with a

modulated chroma part. For component input (YPrPb), there is

no color kill.

Setting CKE to 0 disables color kill.

Setting CKE to 1 (default) enables color kill.

CKILLTHR[2:0] Color Kill Threshold,

Address 0x3D [6:4]

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

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

based (NTSC and PAL) or FM-modulated (SECAM) video

standards.

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

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

ADV7181B may not work satisfactorily for poor input video

signals.

Table 40. CKILLTHR Function

Description

CKILLTHR[2:0]

SECAM

NTSC, PAL

000

No color kill

Kill at < 0.5%

001

Kill at < 5%

Kill at < 1.5%

010

Kill at < 7%

Kill at < 2.5%

011

Kill at < 8%

Kill at < 4.0%

100 (default)

Kill at < 9.5%

Kill at < 8.5%

101

Kill at < 15%

Kill at < 16.0%

110

Kill at < 32%

Kill at < 32.0%

111

Reserved for ADI internal use only. Do not

select.

CHROMA TRANSIENT IMPROVEMENT (CTI)

The signal bandwidth allocated for chroma is typically much

smaller than that of 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 17). Due to the higher bandwidth, the signal transition of

the luma component is usually a lot sharper than that of the

chroma component. The color edge is not sharp but 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 17. CTI Luma/Chroma Transition

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