25/09/04Pazithunzi za digito, ndizosavuta kuganiza kuti kusanja kwapamwamba kumangotanthauza zithunzi zabwinoko. Opanga makamera nthawi zambiri amagulitsa makina otengera ma megapixel, pomwe opanga ma lens amawunikira mphamvu zowunikira komanso zakuthwa. Komabe, m'zochita, mawonekedwe azithunzi samadalira kokha mawonekedwe a lens kapena sensa payokha komanso momwe amafananizira bwino.
Apa ndipamene sampuli za Nyquist zimayambira. Poyambirira mfundo yochokera pakukonza ma siginecha, mulingo wa Nyquist umayika maziko amalingaliro kuti athe kujambula zambiri molondola. Pakujambula, zimatsimikizira kuti mawonekedwe owoneka bwino omwe amaperekedwa ndi lens komanso mawonekedwe a digito a sensor ya kamera amagwira ntchito mogwirizana.
Nkhaniyi imamasula zitsanzo za Nyquist potengera kujambula, ikufotokoza bwino za kusanja kwa kamera ndi kuwala, ndipo imapereka malangizo othandiza pakugwiritsa ntchito kuyambira kujambula mpaka kujambula kwasayansi.
Kodi Nyquist Sampling ndi Chiyani?
Chithunzi 1: Nyquist sampling theorem
Pamwamba:Chizindikiro cha sinusoidal (cyan) chimayesedwa, kapena sampuli, pazigawo zingapo. Mzere wotuwa wautali umayimira muyeso wa 1 pamzere uliwonse wa sinusoidal chizindikiro, kutenga nsonga zazizindikiro zokha, kubisa kwathunthu mawonekedwe enieni a chizindikirocho. Mpendero wofiyira wopindika bwino umagwira miyeso ya 1.1 pachitsanzo chilichonse, kuwulula sinusoid koma kuyimira molakwika ma frequency ake. Izi zikufanana ndi mawonekedwe a Moiré.
Pansi:Pokhapokha zitsanzo ziwiri zikatengedwa pamzere uliwonse (mzere wa madontho ofiirira) m'pamene chizindikiro chenicheni chimayamba kujambulidwa.
Nyquist sampling theorem ndi mfundo yodziwika bwino pakukonza ma siginecha mu zamagetsi, ma audio, kujambula ndi magawo ena. Theorem imamveketsa momveka bwino kuti kumanganso mafupipafupi operekedwa mu chizindikiro, miyeso iyenera kuchitidwa osachepera kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri kawiri le lekikwe, iwonetsedwe mu Chithunzi 1. Pankhani ya kusamvana kwathu kwa kuwala, izi zikutanthauza kuti kukula kwa pixel ya chinthu chathu kuyenera kukhala pafupifupi theka laling'ono kwambiri lomwe tikuyesera kuti tigwire, kapena, ngati microscope, theka la chisankho cha microscope.
Chithunzi 2: Sampling ya Nyquist yokhala ndi ma pixel akulu akulu: zowongolera zimafunikira
Pogwiritsa ntchito kamera yokhala ndi ma pixel a square, 2x sampling factor ya Nyquist theorem imangojambula zolondola zomwe zimagwirizana bwino ndi gridi ya pixel. Ngati mukuyesera kukonza zomanga pakona ya gridi ya pixel, kukula kwake kwa pixel kumakhala kokulirapo, mpaka √2 kukulirapo pa diagonal. Chiwerengero cha zitsanzo chikuyenera kukhala 2√2 kuwirikiza nthawi yomwe mukufuna kuti mujambule zambiri pa 45o ku gridi ya pixel.
Chifukwa cha ichi chikuwonekera poganizira Chithunzi 2 (theka lapamwamba). Tangoganizani kukula kwa pixel kwakhazikitsidwa pakupanga mawonekedwe, ndikupereka nsonga za magwero awiri oyandikana nawo, kapena chilichonse chomwe tikuyesera kuthetsa, aliyense pixel yake. Ngakhale izi zimazindikirika mosiyana, palibe chomwe chikuwonetsa kuti ndi nsonga ziwiri zosiyana - ndipo tanthauzo lathu la "kuthetsa" silinakwaniritsidwe. Pixel pakati pakufunika, kujambula cholumikizira chizindikiro. Izi zimatheka kudzera kuwirikiza kawiri kuchuluka kwa zitsanzo za malo, mwachitsanzo, kuchepetsa kukula kwa pixel ya chinthu.
Optical Resolution vs. Camera Resolution
Kuti timvetsetse momwe sampuli za Nyquist zimagwirira ntchito pazithunzi, tifunika kusiyanitsa mitundu iwiri ya kusamvana:
● Optical Resolution: Imatsimikiziridwa ndi lens, kuwala kwa kuwala kumatanthawuza kutha kwake kutulutsanso tsatanetsatane wabwino. Zinthu monga mtundu wa lens, kabowo, ndi kusokoneza zimayika malire awa. The modulation transfer function (MTF) nthawi zambiri amagwiritsidwa ntchito kuyeza momwe mandala amapatsira kusiyana kwa ma frequency osiyanasiyana.
● Kukhazikika kwa Kamera: Kutengera sensor, kusintha kwa kamera kumadalira kukula kwa pixel, kuchuluka kwa pixel, ndi kukula kwa sensor yonse. Chithunzi cha pixel cha aKamera ya CMOSimatanthauzira molunjika ma frequency ake a Nyquist, omwe amatsimikizira mwatsatanetsatane zomwe sensor imatha kujambula.
Pamene awiriwa sakugwirizana, pamakhala mavuto. Magalasi omwe amaposa mphamvu yothetsa mphamvu ya sensa "yowonongeka", popeza sensayo singathe kujambula zonse. Mosiyana ndi zimenezi, kachipangizo kapamwamba kwambiri kophatikizidwa ndi lens yotsika kwambiri kumabweretsa zithunzi zomwe sizikuyenda bwino ngakhale ma megapixels ambiri.
Momwe Mungasankhire Mawonekedwe a Optical ndi Camera Resolution
Kuyanjanitsa ma optics ndi masensa kumatanthawuza kufananiza ma frequency a Nyquist a sensa ndi ma frequency optical cutoff a lens.
● Mafupipafupi a Nyquist a sensor ya kamera amawerengedwa ngati 1 / (2 × pixel pitch). Izi zimatanthawuza kuchuluka kwapang'onopang'ono kwapang'onopang'ono komwe sensor imatha kuyesa popanda kutchula.
● Mafupipafupi a mawonekedwe a lens amatengera mawonekedwe a lens ndi mawonekedwe ake.
Kuti mupeze zotsatira zabwino, ma frequency a Nyquist a sensor amayenera kulumikizana kapena kupitilira pang'ono kutha kwa mandala. M'malo mwake, lamulo labwino la chala chachikulu ndikuwonetsetsa kuti ma pixel ali pafupifupi theka la mawonekedwe ang'onoang'ono osinthika a lens.
Mwachitsanzo, ngati mandala amatha kuthetsa tsatanetsatane mpaka ma micrometer 4, ndiye kuti sensa yokhala ndi ma pixel a ~ 2 micrometer idzayendetsa bwino dongosolo.
Kufananiza Nyquist ndi Kukhazikika kwa Kamera & Vuto la Ma Pixels Square
Kusinthanitsa ndi kuchepa kwa kukula kwa pixel ya chinthu ndikuchepetsa kusonkhanitsa kuwala. Choncho ndikofunika kulinganiza kufunikira kwa kuthetsa ndi kusonkhanitsa kuwala. Kuonjezera apo, kukula kwa ma pixel a chinthu chachikulu kumapereka mawonekedwe okulirapo a mutu wojambula. Kwa mapulogalamu omwe amafunikira kusamvana bwino, 'rule of thumb' optimum balance akuti ikuwoneka motere: Kukula kwa pixel kwa chinthu, kuchulukitsidwa ndi chinthu china ku akaunti ya Nyquist, kuyenera kukhala kofanana ndi mawonekedwe a kuwala. Kuchuluka kumeneku kumatchedwa kusamvana kwa kamera.
Kuyang'ana ma optics ndi masensa nthawi zambiri kumatsikira kuwonetsetsa kuti kusanja kwachitsanzo kwa kamera kumagwirizana ndi malire a ma lens. Dongosolo limanenedwa kuti "likugwirizana ndi Nyquist" pomwe:
Kamera kusamvana = Kusamvana kwa kuwala
Kumene kusintha kwa kamera kumaperekedwa ndi:
Zomwe zimawerengera Nyquist zomwe nthawi zambiri zimalimbikitsidwa ndi 2.3, osati 2. Chifukwa cha izi ndi chonchi.
Ma pixel a kamera ndi (nthawi zambiri) masikweya, ndipo amakonzedwa pa gridi ya 2-D. Kukula kwa pixel komwe kumatanthauzidwa kuti agwiritsidwe ntchito mu equation moyang'anizana ndi m'lifupi mwake kumayimira kukula kwa mapikseli pamagulu a gululi. Ngati zinthu zomwe tikuyesera kuzithetsa zikanakhala paliponse kupatula kuchulukitsa kokwanira kwa 90 ° kukhudzana ndi gridiyi, kukula kwake kwa pixel kudzakhala kokulirapo, mpaka √2 ≈ 1.41 kuchulukitsa kukula kwa pixel pa 45°. Izi zikuwonetsedwa mu Chithunzi 2 (theka la pansi).
Zomwe zimalangizidwa malinga ndi muyezo wa Nyquist m'njira zonse zitha kukhala 2√2 ≈ 2.82. Komabe, chifukwa cha malonda omwe atchulidwa kale pakati pa chisankho ndi kusonkhanitsa kuwala, mtengo wogwirizana wa 2.3 ukulimbikitsidwa ngati lamulo lachidule.
Udindo wa Nyquist Sampling mu Kujambula
Nyquist sampling ndiye mlonda wa kukhulupirika kwazithunzi. Pamene chiwerengero cha zitsanzo chikutsika pansi pa malire a Nyquist:
● Kuyerekeza pang'ono → kumayambitsa zilembo: mfundo zabodza, m'mphepete mwake, kapena mawonekedwe a moiré.
● Oversampling → imajambula deta yochuluka kuposa momwe makina owonera amatha kubweretsa, zomwe zimapangitsa kuti kubweza kuchepe: mafayilo akuluakulu ndi kufunidwa kwapamwamba kokonzedwa popanda kusintha kowonekera.
Zitsanzo zolondola zimatsimikizira kuti zithunzi ndi zakuthwa komanso zoona zenizeni. Zimapereka malire pakati pa kuyika kwa kuwala ndi kujambula kwa digito, kupeŵa kusamvana kowonongeka kumbali imodzi kapena zolakwika zina.
Mapulogalamu Othandiza
Sampling ya Nyquist si nthano chabe - imakhala ndi ntchito zovuta pamachitidwe azojambula:
● Maikrosikopu:Ofufuza ayenera kusankha masensa omwe amayesa kuwirikiza kambiri kakang'ono kwambiri komwe angathetsedwe ndi mandala omwe akufuna. Kusankha choyeneramicroscope kameraNdikofunikira kwambiri, chifukwa kukula kwa pixel kuyenera kugwirizana ndi kusinthasintha kwapang'onopang'ono kwa cholinga cha maikulosikopu. Ma laboratories amakono nthawi zambiri amakondasCMOS makamera, zomwe zimapereka mphamvu zomveka bwino, zosinthika, ndi mapangidwe abwino a pixel kuti azitha kujambula bwino kwambiri.
● Kujambula:Kuyanjanitsa masensa apamwamba a megapixel okhala ndi magalasi omwe sangathe kuthana ndi mfundo zabwino zofananira nthawi zambiri kumabweretsa kuwongolera konyozeka. Ojambula aluso amalinganiza magalasi ndi makamera kuti asatayike.
● Kujambula:Kuyanjanitsa masensa apamwamba a megapixel okhala ndi magalasi omwe sangathe kuthana ndi mfundo zabwino zofananira nthawi zambiri kumabweretsa kuwongolera konyozeka. Ojambula aluso amalinganiza magalasi ndi makamera kuti asatayike.
● Kuwona kwa Makina &Makamera a SayansiPakuwongolera kwaubwino komanso kuyang'anira mafakitale, kusowa kwazinthu zing'onozing'ono chifukwa cha kucheperako kungatanthauze kuti zida zomwe zili ndi vuto sizidziwika. Kuchulukitsa kutha kugwiritsidwa ntchito mwadala pakuwonera digito kapena kukonza bwino.
Nthawi Yofananira ndi Nyquist: Kuchulukitsa ndi Kudulira
Sampling ya Nyquist imayimira kulinganiza koyenera, koma m'machitidwe, makina ojambulira amatha kuchulukira mwadala kapena kuchepera kutengera kugwiritsa ntchito.
Undersampling ndi chiyani
Pankhani ya mapulogalamu omwe kukhudzika kuli kofunika kwambiri kuposa kuthetsa zing'onozing'ono kwambiri, kugwiritsa ntchito kukula kwa pixel ya chinthu chomwe chili chachikulu kuposa zofuna za Nyquist kungayambitse ubwino wosonkhanitsa kuwala. Izi zimatchedwa undersampling.
Izi zimapereka tsatanetsatane wabwino, koma zingakhale zopindulitsa pamene:
● Kumverera n'kofunika kwambiri: ma pixel akuluakulu amasonkhanitsa kuwala kowonjezereka, kupititsa patsogolo chiŵerengero cha ma signal-to-phokoso pa kujambula kwa kuwala kochepa.
● Kuthamanga n'kofunika: ma pixel ochepa amachepetsa nthawi yowerengera, zomwe zimathandiza kuti anthu azipeza mofulumira.
● Kuchita bwino kwa deta kumafunika: kukula kwa mafayilo ang'onoang'ono ndi abwino m'makina a bandwidth-limited systems.
Chitsanzo: Poyerekeza ndi kashiamu kapena voteji, ma siginecha amasinthidwa pafupipafupi kumadera omwe mukufuna, motero kusayesa pang'ono kumathandizira kusonkhanitsa kuwala popanda kusokoneza zotsatira za sayansi.
Kodi Oversampling ndi chiyani
Mosiyana ndi izi, mapulogalamu ambiri omwe kuthetsera tsatanetsatane ndikofunika kwambiri, kapena kugwiritsa ntchito njira zowunikira pambuyo pogula kuti apezenso zambiri kupyola malire a diffraction, amafuna ma pixel ang'onoang'ono oyerekeza kuposa zomwe Nyquist amafuna, zotchedwa oversampling.
Ngakhale izi sizikuwonjezera kusamvana kowona, zitha kupereka zabwino:
● Imayatsa mawonedwe a digito ndi kutayika kwabwino kwambiri.
● Imawongolera pambuyo pokonza (monga, deconvolution, denoising, super-resolution).
● Amachepetsa zilembo zooneka ngati zithunzi zidzatsitsidwa pambuyo pake.
Chitsanzo: Mu microscope, kamera yowoneka bwino kwambiri ya sCMOS imatha kupitilira ma cellular ma cell kuti ma algorithms apakompyuta azitha kutulutsa zambiri kupitilira malire a diffraction.
Maganizo Olakwika Odziwika
1, Ma megapixels ochulukirapo nthawi zonse amatanthauza zithunzi zakuthwa.
Osati zoona. Kuthwanima kumadalira mphamvu zonse za ma lens komanso ngati ma sensa amatengera moyenera.
2, mandala aliwonse abwino amagwira ntchito bwino ndi sensa iliyonse yokwera kwambiri.
Kusafanana bwino pakati pa kukonza kwa lens ndi kutsika kwa pixel kudzachepetsa magwiridwe antchito.
3, Sampling ya Nyquist ndiyofunikira pakukonza ma sigino, osati kujambula.
M'malo mwake, kujambula kwa digito ndi njira yotsatsira, ndipo Nyquist ndiyofunikira pano monga pamawu kapena mauthenga.
Mapeto
Sampling ya Nyquist ndi yopitilira masamu - ndiye mfundo yomwe imawonetsetsa kuti mawonedwe ndi digito amagwirira ntchito limodzi. Mwa kugwirizanitsa mphamvu yothetsa magalasi ndi luso lachitsanzo la masensa, makina ojambulira amatha kumveka bwino kwambiri popanda zinthu zakale kapena kutaya mphamvu.
Kwa akatswiri m'magawo osiyanasiyana monga ma microscopy, zakuthambo, kujambula, ndi masomphenya a makina, kumvetsetsa sampuli za Nyquist ndizofunikira pakupanga kapena kusankha makina ojambula omwe amapereka zotsatira zodalirika. Pamapeto pake, khalidwe lachithunzi silimabwera chifukwa chokankhira chimodzi mwazinthu monyanyira koma pakukwaniritsa bwino.
FAQs
Kodi chimachitika ndi chiyani ngati sampuli za Nyquist sizikukhutitsidwa ndi kamera?
Chiyembekezo cha zitsanzo chikatsika pansi pa malire a Nyquist, sensa siyingayimire bwino bwino. Izi zimabweretsa dzina lodziwika bwino, lomwe limawoneka ngati m'mphepete mwake, mawonekedwe a moiré, kapena mawonekedwe abodza omwe kulibe kwenikweni.
Kodi kukula kwa pixel kumakhudza bwanji sampuli za Nyquist?
Ma pixel ang'onoang'ono amawonjezera ma frequency a Nyquist, kutanthauza kuti sensor imatha kuthetsa tsatanetsatane. Koma ngati mandala sangathe kupereka mulingo woterowo, ma pixel owonjezera amawonjezera mtengo pang'ono ndipo amatha kukulitsa phokoso.
Kodi sampuli za Nyquist ndizosiyana ndi masensa amtundu wa monochrome vs.
Inde. Mu sensa ya monochrome, zitsanzo za pixel iliyonse zimawunikira mwachindunji, kotero kuti ma frequency a Nyquist ogwira ntchito amafanana ndi ma pixel. Mu sensa yamtundu wokhala ndi fyuluta ya Bayer, njira iliyonse yamtundu imakhala yosatsanzira, chifukwa chake kusinthika kothandiza pambuyo pa demosaicing kumakhala kotsika pang'ono.
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