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3.5.1InputFilterModes
3.5.2ChrominanceRe-samplingOperation
YCbCr 4:2:2 co-sited
input samples
chroma-resampled
capture results
Luma (Y)
sample
-
Chroma (Cb/Cr)
samples
a b c d e f g h i j k l
Cb’
ef
= (-3Cb
c
+ 101Cb
e
+ 33Cb
g
-3Cb
i
) / 128
Cr’
ef
= (-3Cr
c
+ 101Cr
e
+ 33Cr
g
- 3Cr
i
) / 128
3.5.3ScalingOperation
VideoInputFiltering
Theinputfilterhasfourmodesofoperation:no-filtering,½scaling,chrominancere-sampling,and½
scalingwithchrominancere-sampling.FilteroperationisdeterminedbytheCMODE,SCALE,and
RESMPLbitsofVCxCTL.
Table3-10showstheinputfiltermodeselection.When8-bitBT.656orY/Ccaptureoperationisselected
(CMODE=x00),scalingisselectedbysettingtheSCALEbitandchrominancere-samplingisselectedby
settingtheRESMPLbit.If8-bitBT.656orY/Ccaptureisnotselected(CMODE≠x00),filteringis
disabled.
Table3-10.InputFilterModeSelection
VCxCTLBit
CMODERESMPLSCALEFilterOperation
x0000Nofiltering
x0001½scaling
x0010Chrominancere-sampling(fullscale)
x0011½scalingwithchrominancere-sampling
x01xxNofiltering
x10xxNofiltering
x11xxNofiltering
Chrominancere-samplingcomputeschrominancevaluesatsamplepointsmidwaybetweentheinput
luminancesamplesbasedontheinputco-sitedchrominancesamples.Thisfilterperformsthehorizontal
portionofaconversionbetweenYCbCr4:2:2formatandYCbCr4:2:0format.Theverticalportionofthe
conversionmustbeperformedinsoftware.
Thechrominancere-samplingfilterscalculatetheimpliedvalueofCbandCrinbetweenluminance
samplepointsbaseduponnearbyco-sitedCbandCrsamples.Theresultingvaluesareclampedto
between01handFEhandsenttotheCbandCrcapturebuffers.Chrominancere-samplingisshownin
Figure3-8.
Figure3-8.ChrominanceRe-sampling
The1/2scalingmodeisusedtoreducethehorizontalresolutionofcapturedluminanceandchrominance
databyafactoroftwo.ForapplicationsthatrequireonlyCIForlowerresolutions,thisreducesthevideo
capturebuffermemoryrequirements(andthebandwidthneededtowritethebuffer)byafactoroftwo.
Verticalscalingmustbeperformedinsoftware.(Thebandwidthtoloadinthebufferisagainreducedby
50%overthenon-horizontalscaledcase.)
58VideoCapturePortSPRUEM1–May2007
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