25/09/11Kunoma iyiphi isistimu yokulinganisa — kusukela ekuxhumaneni okungenantambo kuya ekuthwebuleni kwedijithali — isilinganiso sesignali-kuya-noise (SNR) siyisilinganiso esiyisisekelo sekhwalithi. Kungakhathaliseki ukuthi uhlaziya izithombe zesibonakude, uthuthukisa ukurekhodwa kwemakrofoni, noma uxazulula inkinga isixhumanisi esingenantambo, i-SNR ikutshela ukuthi lungakanani ulwazi oluwusizo olugqamayo kumsindo wangemuva ongafuneki.
Kodwa ukubala i-SNR ngendlela efanele akulula ngaso sonke isikhathi. Kuye ngesistimu, izici ezengeziwe ezifana nobumnyama obumnyama, umsindo ofundwayo, noma i-pixel binning kungase kudingeke ukuthi kucatshangelwe. Lo mhlahlandlela uhamba nawe kuthiyori, amafomula awumongo, amaphutha avamile, izinhlelo zokusebenza, nezindlela ezingokoqobo zokuthuthukisa i-SNR, iqinisekisa ukuthi ungayisebenzisa ngokunembile kuzo zonke izinhlobo zezimo.
Iyini I-Signal-to-Noise Ratio (SNR)?
Emgogodleni wayo, isilinganiso sesignali-kuya-kumsindo sikala ubudlelwano phakathi kwamandla esignali oyifunayo kanye nomsindo wangemuva oyifihlayo.
● Isiginali = ulwazi olubalulekile (isib., izwi ocingweni, inkanyezi esesithombeni sesibonakude).
● Umsindo = ukushintshashintsha okungahleliwe, okungafuneki okuhlanekezela noma kufihle isignali (isb., i-static, umsindo wezinzwa, ukuphazamiseka kukagesi).
Ngokwezibalo, i-SNR ichazwa ngokuthi:
Ngenxa yokuthi lezi zilinganiso zingahluka kuma-oda amaningi obukhulu, i-SNR ivamise ukuvezwa ngama-decibel (dB):
● I-SNR ephezulu (isb., 40 dB): isignali iyabusa, okuholela olwazini olucacile noluthembekile.
● I-SNR ephansi (isb, 5 dB): umsindo weqa isignali, okwenza ukuhumusha kube nzima.
Ungabala kanjani i-SNR
Ukubalwa kwesilinganiso sesignali ukuya emsindweni kungenziwa ngamaleveli ahlukene okunemba kuye ngokuthi imiphi imithombo yomsindo efakiwe. Kulesi sigaba, kuzokwethulwa amafomu amabili: eyodwa elandisa ubumnyama obukhona kanye nenye ecabanga ukuthi inganakwa.
Qaphela: Ukwengeza amanani omsindo azimele kudinga ukuwengezwa ngamaquadrature. Umthombo ngamunye womsindo uyisikwele, ufingqiwe, futhi impande eyisikwele yengqikithi iyathathwa.
Isilinganiso somsindo wesignali esinomsinga omnyama
Okulandelayo isibalo okufanele sisetshenziswe ezimeni lapho umsindo wamanje omnyama mkhulu ngokwanele ukuze udinge ukufakwa:
Nansi incazelo yamagama:
Isiginali (e-): Lesi isignali yentshisekelo kuma-photoelectrons, ngesignali yamanje emnyama isusiwe
Isiginali Ephelele (e-) izoba isibalo se-photoelectron kuphikseli yentshisekelo - hhayi nje inani lephikseli kumayunithi amaleveli ampunga. Isenzakalo sesibili se-Signal (e-), phansi kwe-equation, umsindo we-photonshot.
I-Dark current (DC):Inani lamanje elimnyama laleyo pixel.
t: Isikhathi sokuchayeka ngamasekhondi
σ:Funda umsindo kwimodi yekhamera.
Isilinganiso somsindo wesignali sobumnyama obunganakwa
Ezimweni ezifushane (< 1 isekhondi) izikhathi zokuchayeka, kanye namakhamera apholile, asebenza kahle kakhulu, umsindo wamanje omnyama ngokuvamile uzoba ngaphansi komsindo ofundekayo, futhi unganakwa ngokuphephile.
Lapho amatemu ephinda echazwe ngenhla, ngaphandle kokuthi isignali yamanje emnyama akudingeki ibalwe futhi isuswe kusiginali njengoba kufanele ilingane noziro.
Imikhawulo yalawa mafomula nemibandela engekho
Amafomula aphikisanayo azonikeza izimpendulo ezifanele ze-CCD kanyeAmakhamera we-CMOS. I-EMCCD namadivayisi aqinisiwe ethula imithombo yomsindo eyengeziwe, ngakho-ke lezi zibalo azikwazi ukusetshenziswa. Ukuze uthole isilinganiso sesilinganiso sesignali-kuya-noise esiphelele kakhulu esibalela lokhu neminye iminikelo.
Elinye igama lomsindo (noma elijwayele ukufakwa) elivame ukufakwa ezilinganisweni ze-SNR yilelo lokungafanani kwesithombe-impendulo (PRNU), futhi ngezinye izikhathi libhalwe 'umsindo wephethini elungisiwe' (FPN). Lokhu kumelela ukungalingani kwenzuzo kanye nokusabela kwesignali kuyo yonke inzwa, engabusa kumasiginali aphezulu uma inkulu ngokwanele, inciphisa i-SNR.
Nakuba amakhamera okuqala ane-PRNU ebalulekile eyanele ukuze adinge ukufakwa kwayo, yesimanjemanjeamakhamera esayensiibe ne-PRNU ephansi ngokwanele ukuze yenze umnikelo wayo ube ngaphansi komsindo we-photon, ikakhulukazi ngemva kokufakwa kokulungiswa ebhodini. Ngakho-ke, manje ngokuvamile ayisanakwa ekubalweni kwe-SNR. Nokho, i-PRNU isabalulekile kwamanye amakhamera nezinhlelo zokusebenza, futhi ifakiwe kuzibalo ezithuthuke kakhulu ze-SNR ukuze kuphelele. Lokhu kusho ukuthi izibalo ezinikeziwe ziwusizo ezinhlelweni eziningi ze-CCD/CMOS kodwa akufanele zithathwe njengezisebenza emhlabeni wonke.
Izinhlobo Zomsindo Ezibalweni ze-SNR
Ukubala i-SNR akukhona nje ukuqhathanisa isignali nenani elilodwa lomsindo. Empeleni, imithombo yomsindo eminingi ezimele iyanikela, futhi ukuyiqonda kubalulekile.
Shot Noise
● Umsuka: ukufika kwezibalo kwamaphothoni noma ama-electron.
● Izikali ezinempande yesikwele yesignali.
● Okuvelele ekuthwebuleni izithombe ezilinganiselwe (i-astronomy, i-fluorescence microscopy).
Umsindo Oshisayo
● Ubuye ubizwe ngomsindo we-Johnson–Nyquist, okhiqizwa ukunyakaza kwama-electron kumaresista.
● Inyuka ngezinga lokushisa kanye nomkhawulokudonsa.
● Okubalulekile ekuxhumaneni ngogesi kanye nokuxhumana okungenantambo.
Umsindo Wamanje Omnyama
● Ukushintsha okungahleliwe kumandla amnyama ngaphakathi kwezinzwa.
● Okubaluleke kakhulu ekuchayekeni okude noma izithonjana ezifudumele.
● Yehliswe ngokupholisa inzwa.
Funda Noise
● Umsindo ovela kuma-amplifiers nokuguqulwa kwe-analog kuya kudijithali.
● Kugxilile ekufundweni ngakunye, kubaluleke kakhulu ezimisweni ezinezimpawu eziphansi.
Quantization Noise
● Kwethulwa ngokwenza amadijithi (ukufinyezwa kumazinga ahlukene).
● Okubalulekile ezinhlelweni zokujula kancane (isb, umsindo we-8-bit).
Umsindo Wemvelo/Wesistimu
● I-EMI, i-crosstalk, i-ripple power supply.
● Ingabusa uma ukuvikela/ukubeka phansi kungalungile.
Ukuqonda ukuthi iyiphi kulezi ehamba phambili kusiza ekukhetheni ifomula efanele kanye nendlela yokunciphisa.
Amaphutha ajwayelekile ekubaleni i-SNR
Kulula ukuhlangana nezindlela eziningi 'zezinqamuleli' zokulinganisa isilinganiso sesignali-kuya-nomsindo ekufanekisweni. Lokhu kuvame ukuba yinkimbinkimbi kakhulu kunezibalo eziphambene, kuvumela ukutholwa okulula kwesithombe ngokwaso kunokudinga ulwazi lwamapharamitha ekhamera afana nomsindo wokufunda, noma kokubili. Ngeshwa, kungenzeka ukuthi ngayinye yalezi zindlela ayilungile, futhi izoholela emiphumeleni esontekile nengasizi. Kunconywa kakhulu ukuthi izilinganiso eziphambene (noma inguqulo ethuthukisiwe kufanele isetshenziswe kuzo zonke izimo.
Ezinye zezinqamuleli ezingamanga ezivame kakhulu zifaka:
1, Ukuqhathanisa ukushuba kwesignali ngokumelene nokuqina kwengemuva, kumazinga ampunga. Le ndlela izama ukwahlulela ukuzwela kwekhamera, amandla esignali noma isilinganiso sesignali kumsindo ngokuqhathanisa ukushuba okuphezulu nokushuba kwangemuva. Le ndlela inephutha elijulile njengoba umthelela we-offset yekhamera ungasetha ngokunganaki ukushuba kwangemuva, inzuzo ingasetha ngokuzenzakalelayo ukuqina kwesignali, futhi akukho mnikelo womsindo kusignali noma ngemuva ocatshangelwayo.
2、 Ukwehlukanisa iziqongo zesignali ngokuchezuka okujwayelekile kwendawo yamaphikseli angemuva. Noma, ukuqhathanisa amanani aphakeme nomsindo obonakalayo ngemuva ovezwe iphrofayela yomugqa. Uma sicabanga ukuthi i-offset isuswe ngendlela efanele kumanani ngaphambi kokuhlukaniswa, ingozi ebaluleke kakhulu kule ndlela ubukhona bokukhanya okungemuva. Noma yikuphi ukukhanya okungemuva ngokuvamile kuzobusa umsindo kumaphikseli angemuva. Ngaphezu kwalokho, umsindo wesibonakaliso sokuthakazelisa, njengomsindo wokudutshulwa, awucatshangelwa nhlobo.
3、Isiginali emaphakathi yamaphikseli entshisakalo uma iqhathaniswa nokuchezuka okujwayelekile kwamanani ephikseli: Ukuqhathanisa noma ukubheka ukuthi isignali ephakemeyo ishintsha kangakanani kumaphikseli angomakhelwane noma amafreyimu alandelanayo aseduze nokuba alungile kunezinye izindlela ezinqamulelayo, kodwa akulula ukugwema amanye amathonya ahlanekezela amanani, njengoshintsho kusiginali engasuki emsindweni. Le ndlela ingase ingalungi ngenxa yokubala kwamaphikseli aphansi uma kuqhathaniswa. Ukususwa kwevelu ye-offset akumele futhi kukhohlakale.
4, Ukubala i-SNR ngaphandle kokuguqulela kumayunithi wokuqina wama-photoelectrons, noma ngaphandle kokukhipha i-offset: Njengoba umsindo we-photon shot ngokuvamile uwumthombo omkhulu womsindo futhi uncika olwazini lokususwa kwekhamera kanye nenzuzo yokukala, akwenzeki ukugwema ukubala emuva kuma-photoelectron ukuze izibalo ze-SNR.
5, Ukwahlulela i-SNR ngeso: Nakuba kwezinye izimo ukwahlulela noma ukuqhathanisa i-SNR ngeso kungaba usizo, kukhona nezingibe ezingalindelekile. Ukwahlulela i-SNR ngamaphikseli yenani eliphezulu kungaba nzima kunevelu ephansi noma amaphikseli angemuva. Imithelela ecashile eyengeziwe ingadlala indima: Isibonelo, iziqapha zekhompuyutha ezihlukene zinganikeza izithombe ngokugqama okuhluke kakhulu. Ngaphezu kwalokho, ukubonisa izithombe kumaleveli e-zoom ahlukene ku-software kungaba nomthelela omkhulu ekubukekeni okubonakalayo komsindo. Lokhu kuyinkinga ikakhulukazi uma uzama ukuqhathanisa amakhamera anosayizi bephikseli yesikhala sento ehlukene. Okokugcina, ukuba khona kokukhanya kwangemuva kungavala noma yimuphi umzamo wokwahlulela i-SNR ngokubukeka.
Izicelo ze-SNR
I-SNR iyimethrikhi yendawo yonke enezinhlelo zokusebenza ezibanzi:
● Umsindo Nokurekhoda Umculo: Inquma ukucaca, ububanzi obuguqukayo, nokwethembeka kokurekhodiwe.
● Ukuxhumana Okungenantambo: I-SNR ihlobene ngokuqondile nezilinganiso zamaphutha ebhithi (BER) kanye nokuphuma kwedatha.
● Ukufanekisa Kwesayensi: Kusayensi yezinkanyezi, ukuthola izinkanyezi ezingaqinile ngokukhanya kwesibhakabhaka kudinga i-SNR ephezulu.
● Izisetshenziswa Zezokwelapha: Izikena ze-ECG, i-MRI, ne-CT zithembele ku-SNR ephezulu ukuhlukanisa amasiginali nomsindo wokuphila.
● Amakhamera Nezithombe: Amakhamera ekhasimende nezinzwa zesayensi ze-CMOS zombili zisebenzisa i-SNR ukuze zilinganisele ukusebenza ekukhanyeni okuphansi.
Ukuthuthukisa i-SNR
Njengoba i-SNR iyisilinganiso esibucayi kangaka, umzamo omkhulu uya ekuyithuthukiseni. Amasu ahlanganisa:
Hardware Izindlela
● Sebenzisa izinzwa ezingcono ezinamandla aphansi amnyama.
● Faka ukuvikela kanye nokwenza phansi ukuze unciphise i-EMI.
● Izithonjana ezipholile zokucindezela umsindo oshisayo.
Izindlela Zesoftware
● Faka izihlungi zedijithali ukuze ususe amaza angafuneki.
● Sebenzisa isilinganiso kuwo wonke amafreyimu amaningi.
● Sebenzisa ama-algorithms okunciphisa umsindo ekuthwebuleni noma ekucubunguleni umsindo.
I-Pixel Binning kanye Nomphumela Wayo ku-SNR
Umthelela wokubopha esilinganisweni sesignali-kuya-kumsindo uncike kubuchwepheshe bekhamera nokuziphatha kwenzwa, njengoba ukusebenza komsindo kwamakhamera aboshwe nangahlanganisiwe kungahluka kakhulu.
Amakhamera e-CCD angakwazi ukushaja amaphikseli aseduze 'ku-chip'. Umsindo wokufunda wenziwa kanye kuphela, nakuba isignali yamanje emnyama evela kuphikseli ngayinye nayo izofingqwa.
Amakhamera amaningi e-CMOS enza i-off-chip binning, okusho ukuthi amanani ayalinganiswa kuqala (futhi afunde umsindo wethulwa), bese afingqwa ngokwedijithali. Umsindo ofundiwe wezifinyezo ezinjalo uyakhula nakuba ukuphindaphindeka ngempande eyisikwele yenani lamaphikseli afingqiwe, okungukuthi ngesici esingu-2 sokuhlanganisa okungu-2x2.
Njengoba ukuziphatha komsindo kwezinzwa kungase kube inkimbinkimbi, ekusetshenzisweni komthamo kuyancomeka ukukala i-offset, ukuzuza, nokufunda umsindo wekhamera kwimodi eboshwe, futhi usebenzise lawa manani esilinganisweni se-signal-to-noise ratio.
Isiphetho
Isilinganiso se-signal-to-noise (SNR) ingelinye lamamethrikhi abaluleke kakhulu kusayensi, ubunjiniyela, nobuchwepheshe. Kusukela ekuchazeni ukucaca kumakholi wefoni kuya ekuvumela ukutholwa kwemithala ekude, i-SNR isekela ikhwalithi yokulinganisa nezinhlelo zokuxhumana. Ukwenza kahle i-SNR akukhona nje ukubamba amafomula ngekhanda — kumayelana nokuqonda okucatshangwayo, imikhawulo, kanye nokuhwebelana komhlaba wangempela. Kusukela kulo mbono, onjiniyela nabacwaningi bangenza izilinganiso ezinokwethenjelwa kanye nezinhlelo zokuklama ezikhipha imininingwane enengqondo ngisho nasezimeni ezinomsindo.
Ufuna ukufunda okwengeziwe? Bheka izindatshana ezihlobene:
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