CCD图像图像处理外文翻译@中英文翻译@外文文献翻译

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1、附录附录1翻译部分RawCCDimagesareexceptionalbutnotperfect.Duetothedigitalnatureofthedatamanyoftheimperfectionscanbecompensatedfororcalibratedoutofthefinalimagethroughdigitalimageprocessing.CompositionofaRawCCDImage.ArawCCDimageconsistsofthefollowingsignalcomponents:IMAGESIGNAL-Thesig

2、nalfromthesource.Electronsaregeneratedfromtheactualsourcephotons.BIASSIGNAL-InitialsignalalreadyontheCCDbeforetheexposureistaken.ThissignalisduetobiasingtheCCDoffsetslightlyabovezeroA/Dcounts(ADU).THERMALSIGNAL-Signal(DarkCurrentthermalelectrons)duetothethermalactivityofthes

3、emiconductor.ThermalsignalisreducedbycoolingoftheCCDtolowtemperature.SourcesofNoiseCCDimagesaresusceptibletothefollowingsourcesofnoise:PHOTONNOISE-Randomfluctuationsinthephotonsignalofthesource.Therateatwhichphotonsarereceivedisnotconstant.THERMALNOISE-Statisticalfluctuation

4、sinthegenerationofThermalsignal.Therateatwhichelectronsareproducedinthesemiconductorsubstrateduetothermaleffectsisnotconstant.READOUTNOISE-Errorsinreadingthesignal;generallydominatedbytheon-chipamplifier.QUANTIZATIONNOISE-ErrorsintroducedintheA/Dconversionprocess.SENSITIVITY

5、VARIATION-SensitivityvariationsfromphotositetophotositeontheCCDdetectororacrossthedetector.ModernCCD'sareuniformtobetterthan1%betweenneighboringphotositesanduniformtobetterthan10%acrosstheentiresurface.NoiseCorrectionsREDUCINGNOISE-ReadoutNoiseandQuantizationNoisearelimitedb

6、ytheconstructionoftheCCDcameraandcannotbeimproveduponbytheuser.ThermalNoise,however,canbereducedbycoolingoftheCCD(temperatureregulation).TheSensitivityVariationscanberemovedbyproperflatfielding.CORRECTINGFORTHEBIASANDTHERMALSIGNALS-TheBiasandThermalsignalscanbesubtractedoutf

7、romtheRawImagebytakingwhatiscalledaDarkExposure.ThedarkexposureisameasureoftheBiasSignalandThermalSignalandmaysimplybesubtractedfromtheRawImage.FLATFIELDING-Arecordofthephotositetophotositesensitivityvariationscanbeobtainedbytakinganexposureofauniformlylit'flatfield".Theseva

8、riationscanthenbedividedoutoftheRawImagetoproduceanimageessentiallyfreefrom