22/04/22Dark Signal Non-Uniformity (DSNU) ndi muyeso wa kuchuluka kwa kusintha kodziyimira pawokha nthawi kumbuyo kwa chithunzi cha kamera. Zimapereka chisonyezero cha manambala amtundu wa chithunzi chakumbuyocho, chokhudzana ndi mapangidwe kapena mapangidwe omwe nthawi zina amapezeka.
Pazithunzi zopepuka, mawonekedwe akumbuyo a kamera amatha kukhala chinthu chofunikira. Ngati palibe mafotoni pa kamera, zithunzi zopezedwa sizidzawonetsa ma pixel a 0 gray levels (ADU). Mtengo wa 'offset' nthawi zambiri umakhalapo, monga 100 imvi, zomwe kamera imawonetsa ngati palibe kuwala, kuphatikiza kapena kuchotsera kukhudzidwa kwa phokoso pamiyezo. Komabe, popanda kuwongolera ndi kukonza mosamalitsa, pangakhale kusintha kwina kuchokera ku pixel kupita ku pixel mumtengo wokhazikikawu. Kusinthaku kumatchedwa 'Fixed Pattern Noise'. DNSU imayimira kukula kwa phokoso lokhazikikali. Imayimira kupatuka kokhazikika kwa milingo ya pixel offset, yoyesedwa mu ma elekitironi.
Pamakamera ambiri oyerekeza otsika, DSNU nthawi zambiri imakhala pansi mozungulira 0.5e-. Izi zikutanthauza kuti pamapulogalamu apakati kapena owala kwambiri okhala ndi zithunzi mazana kapena masauzande ojambulidwa pa pixel imodzi, zopereka zaphokosozi ndizosafunika kwenikweni. Zowonadi, pakugwiritsa ntchito kuwala kochepa, kupereka DSNU ndikotsika kuposa phokoso lowerengedwa la kamera (nthawi zambiri 1-3e-), phokoso lokhazikika ili silingagwire ntchito pazithunzi.
Komabe, DSNU siyoyimira bwino phokoso lokhazikika, chifukwa imalephera kujambula zinthu ziwiri zofunika. Choyamba, makamera a CMOS amatha kuwonetsa mawonekedwe osinthika mosiyanasiyana, nthawi zambiri amakhala ngati mizere ya ma pixel omwe amasiyana pamtengo wawo. Phokoso la 'Fixed Pattern Column Noise' likuwonekera kwambiri m'diso lathu kuposa phokoso losakhazikika, koma kusiyana kumeneku sikuyimiridwa ndi mtengo wa DSNU. Zithunzizi zitha kuwoneka kumbuyo kwa zithunzi zowala kwambiri, monga ngati chizindikiro chapamwamba chomwe chadziwika ndi chosakwana ma electron 100. Kuwona chithunzi 'chokondera', chithunzi chomwe kamera imapanga popanda kuwala, chimakupatsani mwayi wowona ngati pali phokoso lokhazikika.
Kachiwiri, nthawi zina, kusintha kosinthika kosinthika kumatha kutengera nthawi, kusiyanasiyana kuchokera pa chimango chimodzi kupita china. Monga DSNU ikuwonetsa kusiyanasiyana kodziyimira pawokha nthawi, izi sizikuphatikizidwa. Kuwona kutsatizana kwa zithunzi zokondera kumakupatsani mwayi kuti muwone ngati pali phokoso lokhazikika lotengera nthawi.
Monga taonera, DSNU ndi kusiyanasiyana kwapambuyo kwapambuyo sikukhala chinthu chofunikira pakugwiritsa ntchito kuwala kwapakati mpaka kumtunda wokhala ndi ma photon masauzande pa pixel iliyonse, popeza ma signature adzakhala amphamvu kwambiri kuposa kusiyanasiyana.
