參數資料
型號： ADV7189
廠商： Analog Devices, Inc.
英文描述： Multiformat SDTV Video Decoder
中文描述： 標清多格式視頻解碼器
文件頁數： 55/104頁
文件大?。?/td> 890K
代理商： ADV7189
ADV7189
Letterbox Detection
Incoming video signals may conform to different aspect ratios
(16:9 wide screen of 4:3 standard). For certain transmissions in
the wide screen format, a digital sequence (WSS) is transmitted
with the video signal. If a WSS sequence is provided, the aspect
ratio of the video can be derived from the digitally decoded bits
WSS contains.
Rev. A | Page 55 of 104
In the absence of a WSS sequence, letterbox detection may be
used to find wide screen signals. The detection algorithm
examines the active video content of lines at the start and end of
a field. If black lines are detected, this may serve as an indication
that the currently shown picture is in wide screen format.
The active video content (luminance magnitude) over a line of
video is summed together. At the end of a line, this accumulated
value is compared with a threshold, and a decision is made as to
whether or not a particular line is black. The threshold value
needed may depend on the type of input signal; some control is
provided via LB_TH[4:0].
Detection at the Start of a Field
The ADV7189 expects a section of at least six consecutive black
lines of video at the top of a field. Once those lines have been
detected, Register LB_LCT[7:0] reports back the number of
black lines that were actually found. By default, the ADV7189
starts looking for those black lines in sync with the beginning of
active video (e.g., straight after the last VBI video line).
LB_SL[3:0] allows the user to set the start of letterbox detection
from the beginning of a frame on a line-by-line basis. The
detection window closes in the middle of the field.
Detection at the End of a Field
The ADV7189 expects at least six continuous lines of black
video at the bottom of a field before reporting back the number
of lines actually found via the LB_LCB[7:0] value. The activity
window for letterbox detection (end of field) starts in the
middle of an active field. Its end is programmable via
LB_EL[3:0].
Detection at the Midrange
Some transmissions of wide screen video include subtitles
within the lower black box. If the ADV7189 finds at least two
black lines followed by some more nonblack video (e.g.,. the
subtitle) and finally followed by the remainder of the bottom
black block, it reports back a midcount via LB_LCM[7:0]. In
cases where no subtitles are found, LB_LCM[7:0] reports the
same number as LB_LCB[7:0].
Notes
There is a 2-field delay in the reporting of any line count
parameters.
There is no “l(fā)etterbox detected” bit. The user is asked to
read the LB_LCT[7:0] and LB_LCB[7:0] register values and
to come to a conclusion about the presence of letterbox
type video in software.
LB_LCT[7:0] Letterbox Line Count Top (SDP), Address
0x9B, [7:0]; LB_LCM[7:0] Letterbox Line Count Mid (SDP),
Address 0x9C, [7:0]; LB_LCB[7:0] Letterbox Line Count
Bottom (SDP), Address 0x9D, [7:0]
Table 147. LB_LCx Access Information
Signal Name
Block
Address
LB_LCT[7:0]
SDP
0x9B
LB_LCM[7:0]
SDP
0x9C
LB_LCB[7:0]
SDP
0x9D
Register Default Value
Readback only
Readback only
Readback only
LB_TH[4:0] Letterbox Threshold Control (SDP),
Address 0xDC, [4:0]
Table 148. LB_TH Function
LB_TH[4:0]
Description
01100*
Default threshold for detection of black lines.
01101 to
10000
content before identifying nonblack lines).
00000 to
01011
cause the detection of nonblack lines).
*Default value.
Increase threshold (need larger active video
Decrease threshold (even small noise levels can
LB_SL [3:0] Letterbox Start Line (SDP), Address 0xDD, [7:4]
Table 149. LB_SL Function
LB_SL[3:0]
Description
0100*
Letterbox detection is aligned with active video.
Window starts after the EDTV VBI data line. For
example, 0100 = 23/286 (NTSC).
0001, 0010
For example, 0101 = 24/287 (NTSC).
*Default value.
LB_EL[3:0] Letterbox End Line (SDP), Address 0xDD, [3:0]
Table 150. LB_EL Function
LB_EL[3:0]
Description
1101*
Letterbox detection ends with the last active line
of video on a field. For example, 1101 = 262/ 525
(NTSC).
0001,0010
For example, 1100 = 261/524 (NTSC).
*Default value.
Gemstar Data Recovery
The Gemstar compatible data recovery block (GSCD) supports
1× and 2× data transmissions. In addition, it can serve as a
closed caption decoder. Gemstar compatible data transmissions
can occur only in NTSC. Closed caption data can be decoded in
both PAL and NTSC.
The block is configured via I
2
C in the following ways:
GDECEL[15:0] allow data recovery on selected video lines
on even fields to be enabled and disabled.
GDECOL[15:0] enable the data recovery on selected lines
for odd fields.
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相關代理商/技術參數
參數描述
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