 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
ADV7181BBCPZ Datasheet(PDF) 49 Page - Analog Devices |
|
||||||||||||||||||||||||||||||
ADV7181BBCPZ Datasheet(HTML) 49 Page - Analog Devices |
|
|
49 / 96 page  ADV7181B Rev. 0 | Page 49 of 96 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. 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 indicate 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 ADV7181B expects a section of at least six consecutive black lines of video at the top of a field. Once those lines are detected, Register LB_LCT[7:0] reports back the number of black lines that were actually found. By default, the ADV7181B starts looking for those black lines in sync with the beginning of active video, for example, 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 ADV7181B 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 mid- dle 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 ADV7181B finds at least two black lines followed by some more nonblack video, for example, the subtitle, and is then followed by the remainder of the bottom black block, it reports back a midcount via LB_LCM[7:0]. If no subtitles are found, LB_LCM[7:0] reports the same number as LB_LCB[7:0]. There is a 2-field delay in the reporting of any line count parameters. There is no “letterbox detected” bit. The user is asked to read the LB_LCT[7:0] and LB_LCB[7:0] register values and to conclude whether or not the letterbox-type video is present in software. LB_LCT[7:0] Letterbox Line Count Top, Address 0x9B [7:0]; LB_LCM[7:0] Letterbox Line Count Mid, Address 0x9C [7:0]; LB_LCB[7:0] Letterbox Line Count Bottom, Address 0x9D [7:0] Table 60. LB_LCx Access Information Signal Name Address Register Default Value LB_LCT[7:0] 0x9B Readback only LB_LCM[7:0] 0x9C Readback only LB_LCB[7:0] 0x9D Readback only LB_TH[4:0] Letterbox Threshold Control, Address 0xDC [4:0] Table 61. LB_TH Function LB_TH[4:0] Description 01100 (default) Default threshold for detection of black lines. 01101 to 10000 Increase threshold (need larger active video content before identifying non-black lines). 00000 to 01011 Decrease threshold (even small noise levels can cause the detection of non-black lines). LB_SL[3:0] Letterbox Start Line, Address 0xDD [7:4] The LB_SL[3:0] bits are set at 0100b by default. This means that letterbox detection window starts after the EDTV VBI data line. For an NTSC signal, this window is from Line 23 to Line 286. Changing the bits to 0101, the detection window starts on Line 24 and ends on Line 287. LB_EL[3:0] Letterbox End Line, Address 0xDD [3:0] The LB_EL[3:0] bits are set at 1101b by default. This means that letterbox detection window ends with the last active video line. For an NTSC signal, this window is from Line 262 to Line 525. Changing the bits to 1100, the detection window starts on Line 261 and ends on Line 254. Gemstar Data Recovery The Gemstar-compatible data recovery block (GSCD) supports 1× and 2× data transmissions. In addition, it can also serve as a closed caption decoder. Gemstar-compatible data transmissions can only occur in NTSC. Closed caption data can be decoded in both PAL and NTSC. The block is configured via I2C in the following way: • 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. • GDECAD configures the way in which data is embedded in the video data stream. The recovered data is not available through I2C, but is inserted into the horizontal blanking period of an ITU-R. BT656-com- patible data stream. The data format is intended to comply with |
Similar Part No. - ADV7181BBCPZ |
|
Similar Description - ADV7181BBCPZ |
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.COM |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
|
Family Site : ic2ic.com |
icmetro.com |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
