Ekuqaleni kwawo-70s, umbhali waseMelika uMichael Hart waphatha ukufinyelela okungenamkhawulo kukhompyutha ye-Xerox Sigma 5 efakwe eNyuvesi yase-Illinois. Ukuze asebenzise kahle izinsiza zomshini, wanquma ukudala incwadi yokuqala ye-elekthronikhi, ephrinta kabusha iSimemezelo Sokuzimela SaseMelika.
Namuhla, izincwadi zedijithali sezisakazeke kabanzi, ikakhulukazi ngenxa yokuthuthukiswa kwemishini ephathekayo (ama-smartphone, ama-e-readers, ama-laptops). Lokhu kuye kwaholela ekuveleni kwenani elikhulu lamafomethi e-e-book. Ake sizame ukuqonda izici zabo futhi sitshele umlando wezithandwa kakhulu kubo - ake siqale ngefomethi ye-DjVu.
/flickr/ /
Ukuvela kwefomethi
I-DjVu yasungulwa ngo-1996 ngabakwa-AT&T Labs ngenhloso eyodwa - ukunikeza abathuthukisi bewebhu ithuluzi lokusabalalisa izithombe ezinokulungiswa okuphezulu ku-inthanethi.
Iqiniso liwukuthi ngaleso sikhathi i-90% yalo lonke ulwazi lusekhona ephepheni, futhi imibhalo eminingi ebalulekile yayinemifanekiso enemibala nezithombe. Ukuze kugcinwe ukufunda kombhalo kanye nekhwalithi yezithombe, kwakudingeka kwenziwe ukuskena okunokulungiswa okuphezulu.
Amafomethi ewebhu ajwayelekile - i-JPEG, i-GIF ne-PNG - enze kwaba nokwenzeka ukusebenza ngezithombe ezinjalo, kodwa ngenani levolumu. Endabeni ye-JPEG, ukuze umbhalo esikrinini sokuqapha, bekufanele ngiskene idokhumenti ngesinqumo esingu-300 dpi. Ikhasi lombala lomagazini lithatha cishe u-500 KB. Ukulanda amafayela alo sayizi ku-inthanethi kwakuyinqubo enzima kakhulu ngaleso sikhathi.
Okunye kwakuwukwenza amaphepha amaphepha afakwe kudijithali kusetshenziswa ubuchwepheshe be-OCR, kodwa eminyakeni engu-20 edlule ukunemba kwawo kwakukude kabi - ngemva kokucubungula, umphumela wokugcina kwadingeka uhlelwe ngesandla. Ngesikhathi esifanayo, ihluzo nezithombe zahlala "zingaphezu kwamandla". Futhi ngisho noma kwakungenzeka ukushumeka isithombe esiskeniwe embhalweni wombhalo, eminye imininingwane ebonakalayo yalahleka, isibonelo, umbala wephepha, ukuthungwa kwalo, futhi lezi yizingxenye ezibalulekile zemibhalo yomlando.
Ukuze kuxazululwe lezi zinkinga, i-AT&T yathuthukisa i-DjVu. Kwenze kwaba nokwenzeka ukuminyanisa amadokhumenti anombala askeniwe ngokulungiswa okungu-300 dpi kuya ku-40–60 KB, enosayizi wangempela ongu-25 MB. I-DjVu yehlise usayizi wamakhasi amnyama namhlophe ukuze abe ngu-10–30 KB.
I-DjVu icindezela kanjani amadokhumenti
I-DjVu ingasebenza ngawo womabili amadokhumenti ephepha askeniwe namanye amafomethi edijithali, njenge-PDF. Isebenza kanjani i-DjVu ubuchwepheshe obuhlukanisa isithombe sibe izingxenye ezintathu: ingaphambili, ingemuva kanye nemaski emnyama nemhlophe (bit).
Imaski igcinwa ekuxazululweni kwefayela lokuqala futhi isithombe sombhalo neminye imininingwane ecacile - imigqa emihle nemidwebo - kanye nezithombe eziphikisanayo.
Inokulungiswa okungu-300 dpi ukuze igcine imigqa emihle nezinhlaka zezinhlamvu zibukhali, futhi icindezelwa kusetshenziswa i-algorithm ye-JB2, okuwushintsho lwe-algorithm ye-AT&T's JBIG2 yokuthumela ngefeksi. Isici se-JB2 ekwenzayo ukuthi ibheka izinhlamvu eziyimpinda ekhasini futhi igcina izithombe zazo kanye kuphela. Ngakho, emibhalweni enamakhasi amaningi, wonke amakhasi ambalwa alandelanayo abelana “ngesichazamazwi” esivamile.
Ingemuva liqukethe ukuthungwa kwekhasi nemifanekiso, futhi ukulungiswa kwalo kungaphansi kwalokho kwemaski. Ingemuva elingalahleki lilondolozwe ku-100 dpi.
Ngaphambili ulwazi lombala mayelana nemaski, futhi ukulungiswa kwayo kuvame ukuncishiswa nakakhulu, njengoba ezimweni eziningi umbala wombhalo umnyama futhi uyafana ngohlamvu olulodwa oluphrintiwe. Isetshenziselwa ukucindezela ingaphambili nengemuva .
Isigaba sokugcina sokudala idokhumenti ye-DjVu siwumbhalo wekhodi we-entropy, lapho isifaki khodi se-arithmetic esiguquguqukayo siguqula ukulandelana kwezinhlamvu ezifanayo kube inani kanambambili.
Izinzuzo zefomethi
Umsebenzi ka-DjVu wawu "izakhiwo" zombhalo wephepha osesimweni sedijithali, okuvumela ngisho namakhompyutha abuthaka ukuthi asebenze namadokhumenti anjalo. Ngakho-ke, isoftware yokubuka amafayela e-DjVu inamandla “wokunikeza ngokushesha”. Ngiyabonga kuye ngenkumbulo yileso siqephu sekhasi le-DjVu kuphela okufanele siboniswe esikrinini.
Lokhu futhi kwenza kube nokwenzeka ukubuka amafayela “angalandiwe,” okungukuthi, amakhasi ngamanye edokhumenti ye-DjVu enamakhasi amaningi. Kulokhu, umdwebo oqhubekayo wemininingwane yesithombe uyasetshenziswa, lapho izingxenye zibonakala "zivela" njengoba ifayela lilandwa (njengaku-JPEG).
Eminyakeni engu-20 edlule, lapho le fomethi yethulwa, ikhasi lalayishwa ngezigaba ezintathu: okokuqala ingxenye yombhalo yalayishwa, ngemva kwemizuzwana embalwa kwalayishwa izinguqulo zokuqala zezithombe nengemuva. Ngemva kwalokho, lonke ikhasi lencwadi “lavela.”
Ukuba khona kwesakhiwo esinamazinga amathathu nakho kukuvumela ukuthi useshe izincwadi eziskeniwe (njengoba kukhona ungqimba olukhethekile lombhalo). Lokhu kwaba lula uma usebenza nezincwadi zobuchwepheshe kanye nezincwadi zokubhekisela, ngakho i-DjVu yaba yisisekelo semitapo yolwazi eminingana yezincwadi zesayensi. Ngokwesibonelo, ngo-2002 wakhethwa njengenye yefomethi (kanye ne-TIFF ne-PDF) yephrojekthi yokugcina amabhuku askeniwe emithonjeni evulekile.
Ukubi kwefomethi
Nokho, njengabo bonke ubuchwepheshe, i-DjVu inezinkinga zayo. Isibonelo, lapho ubhala ngekhodi ukuskena kwezincwadi kufomethi ye-DjVu, ezinye izinhlamvu kudokhumenti zingase zithathelwe indawo ezinye ezibukeka ngendlela efanayo. Lokhu kuvame ukwenzeka ngezinhlamvu “i” kanye “n”, yingakho le nkinga igama "yin inkinga". Akuxhomekile olimini lombhalo futhi kuthinta, phakathi kwezinye izinto, izinombolo nezinye izinhlamvu ezincane eziphindaphindayo.
Imbangela yawo amaphutha okuhlelwa kwezinhlamvu kusishumeki se-JB2. "Ihlukanisa" iskena ibe ngamaqoqo ezingcezu eziyi-10-20 futhi yakhe isichazamazwi sezimpawu ezijwayelekile zeqembu ngalinye. Isichazamazwi siqukethe izibonelo zezinhlamvu ezivamile nezinombolo ezinamakhasi nezixhumanisi zokubukeka kwazo. Uma ubuka ibhuku le-DjVu, izinhlamvu eziphuma kusichazamazwi zifakwa ezindaweni ezifanele.
Lokhu kukuvumela ukuthi wehlise usayizi wefayela le-DjVu, noma kunjalo, uma ukuboniswa kwezinhlamvu ezimbili kufana ngokubukeka, isishumeki singabadida noma senze iphutha elifanayo. Kwesinye isikhathi lokhu kuholela ekulimaleni kwamafomula embhalweni wezobuchwepheshe. Ukuze uxazulule le nkinga, ungashiya ama-algorithms wokucindezela, kodwa lokhu kuzokwandisa usayizi wekhophi yedijithali yencwadi.
Okunye okungalungile kwefomethi ukuthi ayisekelwe ngokuzenzakalelayo kumasistimu amaningi wokusebenza wesimanje (okuhlanganisa namaselula). Ngakho-ke, ukuze usebenze nayo udinga ukufaka umuntu wesithathu , njenge-DjVuReader, WinDjView, Evince, njll Nokho, lapha ngingathanda ukuqaphela ukuthi abanye abafundi be-electronic (isibonelo, i-ONYX BOOX) basekela ifomethi ye-DjVu "ngaphandle kwebhokisi" - njengoba izinhlelo zokusebenza ezidingekayo sezivele zifakiwe lapho.
Ngendlela, sikhulume ngokuthi yini enye izinhlelo zokusebenza zabafundi abasuselwa ku-Android ezingayenza kokukodwa kokudlule .
Umfundi
Enye inkinga yefomethi ivela lapho usebenza namadokhumenti e-DjVu ezikrinini ezincane zamadivayisi eselula - ama-smartphone, amaphilisi, abafundi. Ngezinye izikhathi amafayela e-DjVu ethulwa ngendlela yokuskena kokusakazwa kwencwadi, futhi izincwadi ezichwepheshile kanye nemibhalo yokusebenza kuvame ukuba ngefomethi ye-A4, ngakho-ke kufanele "uhambise" isithombe lapho ufuna ulwazi.
Nokho, siyaqaphela ukuthi le nkinga nayo ingaxazululeka. Indlela elula, yebo, ukufuna idokhumenti ngefomethi ehlukile - kodwa uma le nketho ingenakwenzeka (isibonelo, udinga ukusebenza ngenani elikhulu lezincwadi zobuchwepheshe ku-DjVu), ungasebenzisa abafundi be-electronic. nge-diagonal enkulu esuka ku-9,7 kuya ku-13,3 amayintshi, "eyenzelwe" ngokukhethekile ukusebenza namadokhumenti anjalo.
Isibonelo, kulayini we-ONYX BOOX amadivaysi anjalo и (ngendlela, silungiselele ukubuyekezwa kwalesi simodeli somfundi, futhi sizoyishicilela maduze kubhulogi yethu), futhi futhi , enesikrini se-E Ink Mobius Carta esine-diagonal engamayintshi angu-10,3 nokulungiswa okunyukile. Imishini enjalo ikuvumela ukuba uhlole ngokucophelela yonke imininingwane yemifanekiso ngobukhulu bayo bokuqala futhi ifanele labo abavame ukufunda izincwadi zemfundo noma zobuchwepheshe. Ukuze ubuke amafayela e-DjVu nawe-PDF I-NEO Reader, ekuvumela ukuthi ulungise ukugqama nokuqina kwamafonti edijithali.
Naphezu kokushiyeka kwefomethi, namuhla i-DjVu isengenye yefomethi ethandwa kakhulu "yokugcina" imisebenzi yemibhalo. Lokhu kubangelwa kakhulu ukuthi yena evulekile, futhi eminye imikhawulo yezobuchwepheshe namuhla ivumela ubuchwepheshe besimanje nentuthuko ukuthi idlule kukho.
Kulezi zinto ezilandelayo sizoqhubeka nendaba mayelana nomlando wokuvela kwamafomethi e-e-book kanye nezici zomsebenzi wabo.
PS Amasethi amaningana abafundi be-ONYX BOOX:
Source: www.habr.com