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Note on Artificial Deformation in Object Shapes Due to Pixelization

机译:关于像素化导致的物体形状的人工变形的注意事项

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Wequalitativelyexaminethepropertiesofartificialdeformationintheshapesofobjects(galaxiesandstars)inducedbypixelizationeffects(alsocalledaliasingeffects)usingtoymocksimulationimages.Twocausesoftheseeffectshavebeenrecognized.Oneisaconsequenceofobservingthecontinuousskywithdiscretepixels,whichiscalleda€?firstpixelizationa€?.Theother,calleda€?secondpixelizationa€?,isaconsequenceofresamplingapixelizedimageontoanotherpixelgridwhosecoordinatesarenotperfectlyadjustedtotheinputgrid.Wepayspecialattentiontothelatter,becauseitmightbeapotentialsourceofasystematicnoiseinweak-lensinganalysis.Inparticular,itisfoundthatresamplingwithrotationinducesartificialellipticitiesinobjectshapeshavingaperiodicconcentric-circle-shapedpattern.Ourmajorfindingsareasfollows:(1)Theroot-mean-square(RMS)ofartificialellipticitiesinobjectshapesinducedbythefirstpixelizationeffectcanbeaslargeasRMS$$gtrsim$$10$$^{-2}$$ifthecharacteristicsizeoftheobjects(e.g.,theFWHM)issmallerthantwiceofthepixelsize.However,forlargerobjects,itquicklybecomesverysmall(RMS$$lesssim$$10$$^{-5}$$).(2)Theamplitudeofshapedeformationinducedbythesecondpixelizationeffectdependsontheobjectsize.Italsodependsstronglyontheinterpolationschemeadoptedtocarryoutresamplingandonthegridsizeoftheoutputpixels.TheRMSofellipticitiesinobjectshapesinducedbythesecondpixelizationeffectcanbesuppressedtowellbelow$$10^{-2}$$ifoneadoptsaproperinterpolationscheme(implementedinpopularimageprocessingsoftwares).Wealsodiscusstheimpactofpixelizationeffectsonaweak-lensinganalysis.
机译:Wequalitativelyexaminethepropertiesofartificialdeformationintheshapesofobjects(galaxiesandstars)inducedbypixelizationeffects(alsocalledaliasingeffects)usingtoymocksimulationimages.Twocausesoftheseeffectshavebeenrecognized.Oneisaconsequenceofobservingthecontinuousskywithdiscretepixels,whichiscalleda€firstpixelizationa€.Theother,calleda€secondpixelizationa€,isaconsequenceofresamplingapixelizedimageontoanotherpixelgridwhosecoordinatesarenotperfectlyadjustedtotheinputgrid.Wepayspecialattentiontothelatter,becauseitmightbeapotentialsourceofasystematicnoiseinweak-lensinganalysis.Inparticular,itisfoundthatresamplingwithrotationinducesartificialellipticitiesinobjectshapeshavingaperiodicconcentric的圆shapedpattern.Ourmajorfindingsareasfollows:????(1 )如果对象(例如FWHM)的特征尺寸小于像素大小的两倍,则由第一个像素化效应引起的对象形状中的人工椭圆率的均方根(RMS)可以大到RMS $$ gtrsim $ 10 $$ ^ {-2} $$。 uicklybecomesverysmall(RMS $$ lesssim $$ 10 $$ ^ { - 5} $$)(2)Theamplitudeofshapedeformationinducedbythesecondpixelizationeffectdependsontheobjectsize.Italsodependsstronglyontheinterpolationschemeadoptedtocarryoutresamplingandonthegridsizeoftheoutputpixels.TheRMSofellipticitiesinobjectshapesinducedbythesecondpixelizationeffectcanbesuppressedtowellbelow $$ 10 ^。{ - 2} $$ ifoneadoptsaproperinterpolationscheme(implementedinpopularimageprocessingsoftwares).Wealsodiscusstheimpactofpixelizationeffectsonaweak-lensinganalysis。

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