Sib tham txog ntau hom Common Halftone Algorithms
Peb yog ib lub lag luam loj hauv Shenzhen Tuam Tshoj. Peb muaj cov phau ntawv luam tawm, phau ntawv nyuaj, phau ntawv luam ntawv, phau ntawv nyuaj, phau ntawv luam tawm, phau ntawv luam tawm, phau ntawv luam tawm, lub thawv ntim, daim qhia ntawv, txhua yam ntawm PVC, cov ntawv luam tawm, ntawv sau cia, hom tshwj xeeb ntawv xim luam tawm khoom, kev ua si cardand li ntawd.
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Halftone technology tau siv hauv kev luam ntawv rau ntau tshaj li ib xyoo thiab tau siv nyob rau hauv cov zis tawm ntau tshaj li 40 xyoo. Nrog rau kev siv cov zis tawm xws li laser printers, inkjet printers, digital printers, digital cameras thiab ntshav duab, digital halftone tshuab tau txais kev saib xyuas ntawm tuam ntxhab thiab cov kev tshawb fawb. Ntxiv nrog rau nws daim ntaub ntawv hauv kev luam tawm thiab cov duab tso tawm, digital halftone technology kuj tau siv rau hauv cov tswv yim ntawm kev cia khoom kom qis, textiles thiab tshuaj. Vim li no, cov tshuab siv tshuab half-hour muaj qhov tseem ceeb ntawm theoretical thiab siv tus nqi.
Raws li peb txhua tus paub, digital halftone technology hais txog technology uas paub txog kev pom ntawm cov dluab ntawm binary (lossis multi-colored binary) raws li tib neeg pom kev coj thiab duab xim cov cwj pwm uas siv cov cuab yeej xws li lej thiab cov computers. . Cov digital halftone yog tus yam ntxwv tsis tshua muaj siab ntawm tib neeg qhov muag. Thaum pom ntawm ib qho chaw nyob deb li cas, tib neeg lub qhov muag xav txog qhov chaw ze ntawm daim duab. Nrog rau tus cwj pwm ntawm no, lub nruab nrab ntawm qhov nruab nrab ntawm grey halftone pom los ntawm tib neeg qhov muag approximates lub zos qhov nruab nrab grey tus nqi ntawm thawj cov duab, li txoj kev nruam laus tone li raws li tus kheej.
Muaj ntau lub tswv yim tau tsim tawm raws li cov qauv kev siv ntawm digital halftones thiab ntau hom. Thaum tso tawm raws li kev ua haujlwm ntawm kev siv algorithm, nws yuav muab faib ua taw tes rau algorithm, kev ua kom sib haum hauv zej zog thiab nws txoj kev. Tus taw tes ua tus txheej txheem yog qhov nyuaj tshaj plaws uas siv cov kev qhia txog kev sib txuas lus los simulate kev txheeb xyuas kev txheeb xyuas kev cai hauv kev lag luam luam, qhov twg txhua pixel chav nyob hauv ib nrab ntawm cov duab uas tau ua los ntawm qhov sib npaug ntawm cov pixel. Txoj kev tseem ceeb tshaj plaws yog qhov kev sib tw ntawm halftone thiab txoj kev dithering; qhov kev sib txeeb ua haujlwm algorithm xam cov ntau ntawm pixels nyob hauv lub zej zog ntawm cov qauv duab tas mus li kom tau ua tiav kom tau qhov pixel tus nqi ntawm cov duab ntawm halftone. Qhov ntau ntawm cov algorithms yog qhov yuam kev diffusion algorithm; nws txoj kev kawm zoo dua yog qhov kev ua raws li qhov kev xav uas yuav tsum tau siv ntau yam kev sib piv kom tau txais ib qho kev pom ntawm halftone duab. Yog li ntawd, nws muaj qhov ntau tshaj plaws ntawm xam. Tsab ntawv tshooj no qhia txog ntau tus neeg sawv cev ntawm cov neeg ib nrab ntawm ib nrab ntawm tus kheej.
Ua ntej, yuam kom dither algorithm (kom dither)
Hauv qhov kev ntsuam xyuas algorithm, cov duab duab tau muab piv rau ib lub sij hawm ntev thim ntawv (los yog hu ua ib qho kev kuaj ntsuas). Ib qho chaw pib thij plaub, qhov twg N qhia txog lub sij hawm ntawm qhov chaw pib thij ntawv.
Rau ib qho chaw pib thetres t (n), nws cov kev txiav txim siab jitter kuaj algorithm yuav piav raws li nram no:
(1) Tus duab tso tawm yuav tsum ua kom zoo li qub, piv txwv li 0 ≤ x (n) ≤ 1. Thaum h (n) = 0, qhov kev sib tw ntawm half-pixel pixel yog lub ntsiab lus dawb, thiab thaum twg h (n) = 1, halftone tawm pixel yog ib tug dub dot. Qhov chaw pib qhov txiav txim siab qhov kev txiav txim uas cov dots ua dub dots raws li qhov ci ntsa iab, uas tseem txiav txim siab qhov zoo ntawm daim duab ntawm halftone. Qhov kev txiav txim dithering algorithm muaj ntau yam ntxwv nrog txawv designs ntawm qhov chaw pib tho txawv. Qhov yooj yim tshais chaw matrix yog ib qho duab hauv txhua qhov pixel yog tus nqi taag: t (n) = 0.5. Yog hais tias tus txheej txheem dithering algorithm nrog xws li ib lub cim matrix thov rau daim duab, feem ntau ntawm cov ntsiab lus ntawm cov duab nruas duab ploj, thiab qhov sib npaug ntawm cov duab ib nrab tau muaj ib qho loj distortion piv rau daim tseem nruam duab.
Feem ntau, yuam kom jitter faib ua qhov point-aggregated kom jitter thiab point-discrete order jitter. Qhov kev ntsuam xyuas ntawm lub ntsiab lus ntawm qhov sib sau ua ke yuav tsum tau ua kom zoo zoo rau kev sim ua kom tiav. Thaum lub pixel ceev ntawm lub duab tujtaws tsis hloov, txo cov dots yuav tsum generated nyob ib ncig ntawm lub pixels. Txoj cai tsim cov ntsiab lus rau kev taw qhia kom tau qhov sib txawv ntawm cov lus pom zoo los ntawm Bayer. Nws kev tshawb fawb qhia tias cov visibility ntawm cov khoom siv tsis yog zoo tagnrho los ntawm Fourier tsom ntawm cov qauv ntawm kev sib txawv ntawm ntau qhov sib txawv. Thaum cov qauv ntawm cov xim tsis muaj xim zoo ib yam ntawm cov wavelengths sib txawv, qhov tivthaiv sib thooj rau qhov ntev tshaj wavelength hauv lub qhov kawg ntawm qhov ntev yog qhov kev tivthaiv nrog kev pom kev siab tshaj plaws. Raws li tus txheej txheem no, Bayer tsim ib qho kev ntsuas kev txheeb xyuas qhov nruab nrab, thiab qhov kev sib tw ntawm halftone tau los ntawm kev siv cov lus taw qhia discrete thiab yuam jitter ntawm no zuag qhia txog cov ntsiab lus ntxiv.
Txawm hais tias qhov point-discrete ordered jitter preserves ntxiv, vim "ntxiv rau dots", taw tes-aggregated yuam jitter feem ntau siv nyob rau hauv daim ntaub ntawv. Qhov kev nce nqi yog tshwm sim los ntawm qhov tsis yog qhov zoo ntawm lub tshuab luam ntawv, txawm tias nws muaj peev xwm pom tau tias ib lub tshuab luam ntawv zoo tshaj plaws tsim tau cov teeb meem uas muaj cov kab sau ua ntej xws li squares, tab sis cov dots raug tsim los ntawm lub diffusion ntawm number case los ntawm pre-defined geometries rau lwm tus pixels. Nce qhov tshwm sim. Thaum lub pixel ntom ntawm cov duab tujtaws tsis hloov, qhov dot yuav tsum generated ntawm cov pixels surrounding, yog li cov teev-sau yuam jitter feem ntau yuav tiv thaiv cov khoom poob nyiaj, li no txo qhov teev tau txais txiaj ntsim hauv cov duab ib nrab ntawm cov duab tag nrho.
Qhov ob, qhov yuam kev diffusion algorithm (yuam kev Diffusion)
Qhov yuam kev diffusion algorithm yog ib qho nrov thiab halftone effect algorithm, uas yog thawj zaug npaj los ntawm Floyed-Steinberg. Qhov kev siv algorithm no yuav tsum muaj kev sib txoos ua ke, uas muab ib nrab kev zoo dua rau kev tshaj tawm thiab tsis ua rau qhov khoom poob nce, ua rau muaj kev sib txig ib nrab ntawm cov duab nrog ib qho pauv ntawm pixels.
Cov tswv yim yooj yim yog xub thawj cov duab pixels raws li qee tus luam theej duab qis, thiab tom qab ntawd kis tau qhov kev ua qis ntau npaum licas rau cov tsis muaj pixels uas nyob ib sab. Daim duab teeb meem ntawm qhov yuam kev diffusion muaj nyob rau hauv Xam 1.
Daim duab 1 Qhov teeb meem diffusion schematic
Qhov twg Q (.) Yog qhov pib ua num, u (m, n) yog qhov lej ntawm tus nqi ntawm qhov pixel thiab qhov kev ua qes ib nrab. Thaum u (m, n) siab dua qhov chaw pib, Q (.) Tus nqi yog l, txwv tsis pub tus nqi yog 0. e (m, n) yog qhov ua yuam kev, x (m, n) , x (m, n) ∈ [0,1]. Kev ua tiav ntawm u (m, n) tau tshwm sim nyob rau hauv ib lub teeb liab sawv cev b (m, n), b (m, n) ∈ [0,1]. H yog ib qho kev limphem nrug nrog lub lim coefficient ntawm h (k, l) thiab nws nyob.
Qhov yuam kev diffusion algorithm tau qhia los ntawm cov qauv nram qab no: (2) - (4)
Qhov peb, taw tes diffusion (Dot Diffusion)
Tus taw tes kis halftone algorithm npaj los ntawm Knuth yog ib qho algorithm uas qhia txog kev ua haujlwm thaum uas sim ua kom muaj qhov zoo ntawm txoj kev yuam kev. Qhov kis kis algorithm muaj tsuas yog ib qho tsim parameter, hoob Matrix C, uas txiav txim siab qhov kev txiav txim uas cov pixels tau ua tiav los ntawm halftones. Txoj hauj lwm ntawm lub nruas duab duab pixel muab faib ua IJ cov chav kawm, thiab kuv thiab J yog cov tsis hloov zuj zus. Cov lus 1 yog ib qho piv txwv ntawm ib qho khoom siv hauv nruab nrab nrog 64 zauv hauv lub rooj.
Rooj ntawv 1 8 × 8 optimization chav kawm ntawv
Txheeb xyuas ib tug duab nruam cov duab uas nws qhov pixel qhov tseem ceeb yog ua haujlwm, rau ib qhov kev npaj, peb ua txhua yam pixels rau chav kawm ntawv k thiab txhais kom ib nrab hnub pixel qhov tseem ceeb li hauv qab no:
(5) Qhov yuam kev, los ntawm kev soj ntsuam yim lub, hloov qhov tseem ceeb ntawm cov neeg zej zog nrog cov chav kawm ntawv siab nrog cov qub kev nruam duab duab pixel qhov tseem ceeb (piv txwv li, cov uas tsis tau ua tiav los ntawm halftones). Hauv ntej, ib qho chaw nyob ze nrog ntau dua cov chav kawm yog hloov nrog:
Rau cov neeg sab nraud, (6-a)
Rau kab pheeb ces kaum sib dhos, (6-b)
Ntawm lawv, nws yog los xyuas kom meej tias tag nrho cov teeb meem ntxiv rau tag nrho cov zej zog yog raws nraim. Lub zej zog txoj cai-angle muaj ib qho ntxiv parameter 2 vim qhov uas tsis nyob rau hauv cov kab rov tav thiab feem ntsug cov lus qhia ntau dua li qhov uas tsis nyob hauv txoj kab kev taw qhia kab pheeb ces kaum.
Tom qab ntawd, cov nruam laus pixel nrog rau chav kawm ntawv k + 1 kuj tau txais kev kho mob zoo sib xws. Tam sim no tus nqi pixel tsis yog tus qub nrig tone pixel tus nqi, tab sis kev kho raws li cov mis (6). Tom qab qhov algorithm aborted, Lub teeb liab yog ib nrab hnub tshwm sim.
Daim duab 2 yuam kev kis los ntawm ib qho pixel rau zej zog
Daim duab 2 qhia txog tus txheej txheem ntawm kis. Cov lej hauv cov duab xis yog lub ntsiab ntawm cov chav kawm ntawv, cov lej ntawm cov voj voos yog qhov sib txawv ntawm qhov sib txawv ntawm cov diffusion coefficients, thiab cov zej zog muaj cov chav kawm siab dua 33 yog 58, 45, 42, 40., 63, 47. kev ua yuam kev tsim tawm ntawm 33 yog muab faib rau cov neeg txawv ntawm qhov sib txawv raws li qhov sib npaug ntawm qhov sib npaug ntawm qhov sib ntxiv ntawm cov diffusion coefficients, uas hauv qhov ua piv txwv yog 2 + 1 + 2 + 1 + 2 + 1 = 9. Tom qab ntawd muab koj tso rau hauv lub zej zog txoj cai-kaum thiab 2e nyob rau hauv zej zog kab pheeb ces kaum. Vim tias muaj 64 theem hauv tag nrho, qhov algorithm tiav hauv 64 theem.
Qeb plaub, nws qhov kev ntsuas half-algorithm
Lub tswv yim ntawm qhov kev xav ntawm qhov half-algorithm yog ua ntej tau txais thawj zaug ib nrab ntawm cov duab los ntawm ib txoj kev yooj yim, thiab tom qab ntawd ces ua rau txheej thaum pib ib nrab ntawm cov duab, kom lub halftone duab tau los ntawm txhua tus txheej txheem muaj me yuam kev, thiab thaum kawg pom qhov kawg. Yav tom ntej ntawm daim duab. Qhov zoo ntawm qhov iterative halftone algorithm yog tias tus resulting halftone duab tau zoo heev pom teebmeem, yeej tseem tsis muaj cov qauv zoo nkauj; thiab muaj peev xwm ntawm kev tsim cov lus nplua nuj tones. Txawm li cas los xij, raws li qhov nyuaj ntawm qhov teeb meem ntawm qhov kev siv ntawm qhov kev ua no, qhov tseem ceeb ntawm qhov kev siv sijhawm ntawm ib nrab hnub yog qhov nyuaj rau siv nyob rau hauv cov sijhawm ua haujlwm tiag thiab tsuas yog siv los ua ib qho kev xeem.
Kev tshawb nrhiav txoj kev ncaj qha binary (DBS) siv qhov HVS qauv thiab tus qauv ntaus ntawv kom txo tau qhov kev pom ntawm qhov kev pom ntawm half-image duab thiab cov duab nruam tas mus li. HVS qauv yog sawv cev los ntawm txoj kev hloov ntawm txoj kab uas tsis tshua muaj siab dhau. Cov lus teb ntawm qhov lim tshaj qhov no txhais tias yog li nram qab no:
(7)
Qhov sib txawv ntawm qhov sib txawv ntawm qhov sib txawv ntawm lub retina, L yog qhov nruab nrab qhov ci, c = 0.525 d = 3.91.
Cia e [m, n] txhais cov duab yuam kev thiab txhais kom meej (8)
Qhov twg f [m, n] yog ib cov duab nruam tas mus li thiab g [m, n] yog ib qho kev sib thooj ib nrab duab, pom qhov yuam kev pom ntawm halftone duab thiab cov duab nruam duab tuaj yeem hais tau (9)
Qhov twg X sib sau mus rau qhov raster ntawm qhov chaw nyob tau ntawm cov khoom tso tawm; thiab tus taw tes luam tawm tau sab nraud nrog lub lim, peb yuav xav tias muaj ntau yam ntau dua.
Tag nrho yuam kev ntawm tag nrho halftone duab uas ua los ntawm DBS thiab cov duab qub yog:
(10) Substituting (9) mus rau (10), E muab xam raws li hauv qab no
(11) Ntawm lawv yog kev kho cov kab ke ntawm cov ntsiab lus nruab nrab ntawm cov kab ntawv luam tawm.
DBS siv cov kev pab cuam sib pauv hloov los txo qhov kev ua yuam kev E. Qhov no algorithm scans tag nrho halftone duab thiaj li sab laug mus rau sab xis thiab saum toj mus rau hauv qab, pib ntawm qhov tau txais thawj zaug ntawm daim duab, rau txhua qhov ntawm halftone dluab. Lub pixel ntsuas cov nyhuv ntawm cov duab pert thiab cov nqi ntawm halftone duab tau los ntawm kev sib pauv nws cov nqi nrog qhov chaw surrounding yim pixels. Yog hais tias ib qho ntawm cov kev hloov txo qhov yuam kev, qhov pom tau hais tias ua rau qhov yuam kev txo yog khaws cia, thiab cov txheej txheem saum toj no tau ua dua rau ntawm half-hour duab txog thaum tag nrho cov txheej txheem tsis muaj kev hloov ua haujlwm, thiab DBS algorithm xaus.
V. Lus xaus
Feem ntau, nyob rau hauv cov kev sib tw ntawm halftone, qhov zoo tshaj plaws halftone daim duab zoo ua yog ib qho kev siv algorithm, tab sis vim yog lub complexity ntawm lub le caag, nws feem ntau tsis siv nyob rau hauv real-time algorithms. Qhov yuam kev diffusion algorithm yog tam sim no lub nrov tshaj plaws halftone algorithm, thiab lub resulting halftone duab tsis muaj cuab kev moiré thiab zoo pom kev nyhuv. Lub dithering algorithm yog yooj yim rau kev siv, tab sis nws muaj tej yam tsis xws luag hauv kev tu tsiaj tu, kev daws teeb meem thiab pom kev ntxhib los mos. Qhov kis kis algorithm siv thaum ua haujlwm, tiam sis qhov zoo ntawm halftone duab xav tau zoo tuaj.