ADV7189KST Analog Devices Inc, ADV7189KST Datasheet - Page 36

• Manufacturer Part Number: ADV7189KST
• Description: IC VIDEO DECODER NTSC 80-LQFP
• Manufacturer: Analog Devices Inc
• Type: Video Decoderr

Specifications of ADV7189KST

• Applications: Set-Top Boxes, Video Players, Recorders
• Voltage - Supply, Analog: 3.15 V ~ 3.45 V
• Voltage - Supply, Digital: 1.65 V ~ 2 V
• Mounting Type: Surface Mount
• Package / Case: 80-LQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

ADV7189
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, can lead to some visual
artifacts when it comes to sharp color transitions. At the border
of two bars of color, both components (luma and chroma)
change at the same time (see Figure 18). 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 is blurred, in the worst case, over
several pixels.
The chroma transient improvement block examines the input
video data. It detects transitions of chroma, and can be pro-
grammed to “steepen” the chroma edges in an attempt to
artificially restore lost color bandwidth. The CTI block,
however, only operates on edges above a certain threshold to
ensure that noise is not emphasized. Care has been taken to
ensure that edge ringing and undesirable saturation or hue
distortion are avoided.
Chroma transient improvements are needed primarily for
signals that experience severe chroma bandwidth limitation.
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]
The CTI_EN bit enables the CTI function. If set to 0, the CTI
block is inactive and the chroma transients are left untouched.
Table 75. CTI_EN Function
CTI_EN
0 (default)
1
DEMODULATED
CHROMA
SIGNAL
SIGNAL
LUMA
Figure 18. CTI Luma/Chroma Transition
Description
Disable CTI.
Enable CTI block.
SHARPENED CHROMA TRANSITION
AT THE OUTPUT OF CTI
LUMA SIGNAL WITH A
TRANSITION, ACCOMPANIED
BY A CHROMA TRANSITION
ORIGINAL, "SLOW" CHROMA
TRANSITION PRIOR TO CTI
Rev. B | Page 36 of 104
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.
Table 76. CTI_AB_EN Function
CTI_AB_EN
0
1 (default)
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 effective, 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
can also increase the visual impact of small amplitude, high
frequency chroma noise.
Table 77. CTI_AB Function
CTI_AB[1:0]
00
01
10
11 (default)
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.
Table 78. CTI_C_TH Function
CTI_C_TH[7:0]
0x08 (default)
Description
Disable CTI alpha blender.
Enable CTI alpha-blend mixing function.
Description
Sharpest mixing between sharpened and
original chroma signal.
Sharp mixing.
Smooth mixing.
Smoothest alpha-blend function.
Description
Threshold for chroma edges prior to CTI.