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3.2.3BT.656ImageWindowandCapture
Capture Image
Ystart
Xstart
Ystop
Xstop
Field 1
Capture Image
Ystart
Xstart
Ystop
Xstop
Field 2
Hcount=0
Ycount=1
Ycount=1
BT.656VideoCaptureMode
Table3-4.ErrorCorrectionbyProtectionBits(continued)
ReceivedF,V,andHBits
ReceivedP
3
-P
0
Bits000001010011100101110111
1011010-010010-101010-
1100-001110-110-110110
1101001001-001-001110-
1110---011-101110-
1111-001010-100---
TheBT.656formatisaninterlacedformatconsistingoftwofields.Thevideoportallowscaptureofoneor
bothfields.Thecapturedimageisasubsetofeachfieldandcanbelargerorsmallerthantheactivevideo
region.ThecapturedimagepositionisdefinedbytheVCxSTRT1andVCxSTOP1registersforfield1,and
theVCxSTRT2andVCxSTOP2registersforfield2.TheVCXSTARTandVCXSTOPbitssetthe
horizontalwindowpositionforthefieldrelativetotheHCOUNTpixelcounter.TheVCYSTARTand
VCYSTOPbitssettheverticalpositionrelativetotheVCOUNTlinecounter.ThisisshowninFigure3-1.
HCOUNTincrementsoneverychromasampleperiod(everyotherVCLKINrisingedge)forwhichcapture
isenabled.OnceVCOUNT=YSTART,linecapturebeginswhenHCOUNT=XSTART.Itcontinuesuntil
HCOUNT=XSTOP.Afield'scaptureiscompletewhenHCOUNT=VCXSTOPandVCOUNT=
VCYSTOP.
Figure3-1.VideoCaptureParameters
Table3-5showscommondigitalcamerastandardsandthenumberoffieldspersecond,numberofactive
linesperfield,andthenumberofactivepixelsperline.
48VideoCapturePortSPRUEM1–May2007
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