A farkon 70s, marubucin Amurka Michael Hart ya gudanar Unlimited damar zuwa kwamfutar Xerox Sigma 5 da aka shigar a Jami'ar Illinois. Don yin amfani da albarkatun na'ura da kyau, ya yanke shawarar ƙirƙirar littafin lantarki na farko, yana sake buga sanarwar 'Yancin Amurka.
A yau, adabin dijital ya zama tartsatsi, galibi godiya ga haɓakar na'urori masu ɗaukar hoto (wayoyin hannu, masu karanta e-readers, kwamfyutoci). Wannan ya haifar da bullar nau'ikan nau'ikan e-littattafai masu yawa. Bari mu yi ƙoƙarin fahimtar fasalin su kuma mu faɗi tarihin shahararrun su - bari mu fara da tsarin DjVu.
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Fitowar tsarin
An kirkiro DjVu a cikin 1996 ta AT&T Labs tare da manufa ɗaya - don baiwa masu haɓaka gidan yanar gizo kayan aiki don rarraba hotuna masu ƙarfi akan Intanet.
Gaskiyar ita ce, a lokacin 90% na duk bayanan suna nan a kan takarda, kuma yawancin muhimman takardu suna da hotuna masu launi da hotuna. Don ci gaba da karantawa na rubutu da ingancin hotuna, ya zama dole don yin sikanin ƙira.
Tsarin gidan yanar gizo na gargajiya - JPEG, GIF da PNG - sun ba da damar yin aiki tare da irin waɗannan hotuna, amma a farashin girma. A cikin yanayin JPEG, don haka rubutu akan allon saka idanu, dole ne in duba takaddar tare da ƙudurin 300 dpi. Shafin launi na mujallar ya mamaye kusan 500 KB. Zazzage fayiloli masu girman wannan daga Intanet aiki ne mai tsananin aiki a wancan lokacin.
Madadin shine a ƙididdige takaddun takarda ta amfani da fasahar OCR, amma shekaru 20 da suka gabata daidaitonsu bai dace ba - bayan sarrafawa, sakamakon ƙarshe dole ne a gyara shi da hannu. A lokaci guda, zane-zane da hotuna sun kasance "fice". Kuma ko da za a iya sanya hoton da aka zana a cikin takardar rubutu, an rasa wasu bayanai na gani, alal misali, launin takarda, da rubutunta, kuma waɗannan abubuwa ne masu muhimmanci na takardun tarihi.
Domin magance waɗannan matsalolin, AT&T ya haɓaka DjVu. Ya ba da damar damfara takaddun launi da aka bincika tare da ƙudurin 300 dpi zuwa 40-60 KB, tare da girman asali na 25 MB. DjVu ya rage girman shafukan baki da fari zuwa 10-30 KB.
Yadda DjVu ke matsawa takardu
DjVu na iya aiki tare da takaddun takarda da aka bincika da sauran nau'ikan dijital, kamar PDF. Yadda DjVu ke aiki fasahar da ke raba hoton zuwa sassa uku: gaba, bango da baki da fari (bit) abin rufe fuska.
Ana ajiye abin rufe fuska a ƙudurin ainihin fayil ɗin kuma Hoton rubutu da sauran cikakkun bayanai - layi mai kyau da zane-zane - da kuma hotuna masu bambanta.
Yana da ƙuduri na 300 dpi don kiyaye layi mai kyau da bayyani masu kaifi, kuma ana matsawa ta amfani da JB2 algorithm, wanda shine bambancin AT&T's JBIG2 algorithm don faxing. Farashin JB2 abin da yake yi shi ne yana neman kwafin haruffa a shafin kuma yana adana hoton su sau ɗaya kawai. Don haka, a cikin takaddun shafuka masu yawa, kowane ƴan shafuka masu jere suna raba “kamus” gama gari.
Bayanan baya yana ƙunshe da rubutun shafi da misalai, kuma ƙudurinsa ya yi ƙasa da na abin rufe fuska. An adana bayanan mara asara a 100 dpi.
Gaba bayanin launi game da abin rufe fuska, kuma ƙudurinsa yawanci yana raguwa har ma da ƙari, tunda a mafi yawan lokuta launin rubutu baƙar fata ne kuma iri ɗaya ne ga ɗabi'ar da aka buga. Ana amfani dashi don damfara gaba da baya .
Mataki na ƙarshe na ƙirƙirar daftarin aiki DjVu shine entropy encoding, lokacin da rikodin lissafin daidaitacce ya juya jerin haruffa iri ɗaya zuwa ƙimar binary.
Amfanin tsarin
Aikin DjVu ya kasance "kayayyakin" na takarda takarda a cikin nau'i na dijital, yana ba da damar ko da ƙananan kwakwalwa suyi aiki tare da irin waɗannan takardun. Saboda haka, software don duba fayilolin DjVu yana da ikon "saurin yin sauri". Godiya gareta a cikin ƙwaƙwalwar ajiya kawai wannan yanki na shafin DjVu wanda yakamata a nuna akan allon.
Wannan kuma yana ba da damar duba fayilolin "wanda ba a sauke ba", wato, shafuka ɗaya na takaddun DjVu mai shafuka masu yawa. A wannan yanayin, ana amfani da zane mai ci gaba na bayanan hoto, lokacin da abubuwan da aka gyara suna da alama suna “bayyana” kamar yadda aka zazzage fayil ɗin (kamar a cikin JPEG).
Shekaru 20 da suka gabata, lokacin da aka gabatar da wannan tsari, an loda shafin a matakai uku: na farko an loda bangaren rubutun, bayan dakika biyu aka loda sigar farko na hotuna da bayanan baya. Bayan haka, dukan shafin na littafin "ya bayyana."
Kasancewar tsarin matakai uku kuma yana ba ku damar bincika ta littattafan da aka bincika (kamar yadda akwai rubutun rubutu na musamman). Wannan ya zama mai dacewa yayin aiki tare da wallafe-wallafen fasaha da littattafan tunani, don haka DjVu ya zama tushen yawancin ɗakunan karatu na littattafan kimiyya. Misali, a shekarar 2002 aka zabe shi a matsayin ɗaya daga cikin tsarin (tare da TIFF da PDF) don aikin adana littattafan da aka bincika daga buɗaɗɗen maɓuɓɓuka.
Lalacewar tsarin
Koyaya, kamar duk fasahohin, DjVu yana da nasa drawbacks. Misali, lokacin shigar da sikanin littattafai cikin tsarin DjVu, ana iya maye gurbin wasu haruffa a cikin takaddar da wasu waɗanda suke kama da kamanni. Wannan ya fi faruwa da haruffan "i" da "n", wanda shine dalilin da ya sa wannan matsala suna "yin matsala". Ba ya dogara da harshen rubutun kuma yana tasiri, a tsakanin sauran abubuwa, lambobi da sauran ƙananan haruffa masu maimaitawa.
Dalilinsa shine kurakuran rarrabuwar haruffa a cikin mai rikodin JB2. Yana "raba" yana dubawa zuwa ƙungiyoyin guda 10-20 kuma ya samar da ƙamus na alamomin gama gari ga kowace ƙungiya. Kamus ɗin ya ƙunshi misalan haruffa na gama-gari da lambobi tare da shafuka da daidaita bayyanar su. Lokacin da kuka duba littafin DjVu, ana saka haruffa daga ƙamus zuwa wuraren da suka dace.
Wannan yana ba ku damar rage girman fayil ɗin DjVu, duk da haka, idan nunin haruffa biyu sun yi kama da na gani, mai ɓoyewa na iya ko dai ya rikitar da su ko kuskuren su iri ɗaya. Wani lokaci wannan yana haifar da lalacewa ga ƙididdiga a cikin takaddun fasaha. Don magance wannan matsalar, zaku iya barin matsawa algorithms, amma wannan zai ƙara girman kwafin dijital na littafin.
Wani rashin lahani na tsarin shi ne rashin goyan bayan shi a yawancin tsarin aiki na zamani (ciki har da na wayar hannu). Don haka, don yin aiki tare da shi kuna buƙatar shigar da ɓangare na uku , irin su DjVuReader, WinDjView, Evince, da dai sauransu Duk da haka, a nan ina so in lura cewa wasu masu karatu na lantarki (misali, ONYX BOOX) suna goyan bayan tsarin DjVu "daga cikin akwatin" - tun da an riga an shigar da aikace-aikacen da suka dace a can.
Af, mun yi magana game da abin da aikace-aikace na tushen Android masu karatu za su iya yi a daya daga cikin baya .
Mai karatu
Wani matsala na tsarin yana bayyana lokacin aiki tare da takardun DjVu akan ƙananan fuska na na'urorin hannu - wayoyin hannu, kwamfutar hannu, masu karatu. Wani lokaci ana gabatar da fayilolin DjVu a cikin nau'i na sikanin yada littafi, kuma ƙwararrun wallafe-wallafen da takardun aiki suna sau da yawa a cikin tsarin A4, don haka dole ne ku "motsa" hoton don neman bayanai.
Duk da haka, mun lura cewa ana iya magance wannan matsala. Hanya mafi sauƙi, ba shakka, ita ce neman takarda a cikin wani tsari daban-daban - amma idan wannan zaɓin ba zai yiwu ba (alal misali, kana buƙatar yin aiki tare da babban adadin wallafe-wallafen fasaha a DjVu), to, zaka iya amfani da masu karatu na lantarki. tare da babban diagonal daga 9,7 zuwa 13,3 inci, wanda musamman "wanda aka keɓe" don aiki tare da irin waɗannan takardu.
Misali, a layin ONYX BOOX irin wadannan na'urori sune и (ta hanyar, mun shirya bita na wannan samfurin mai karatu, kuma nan ba da jimawa ba za mu buga shi a kan shafinmu), da ma , wanda ke da allon E Ink Mobius Carta tare da diagonal na inci 10,3 da ƙarin ƙuduri. Irin waɗannan na'urori suna ba ku damar bincika duk cikakkun bayanai na misalai a cikin girmansu na asali kuma sun dace da waɗanda galibi suna karanta wallafe-wallafen ilimi ko fasaha. Don duba fayilolin DjVu da PDF NEO Reader, wanda ke ba ku damar daidaita bambanci da kauri na rubutun lambobi.
Duk da gazawar tsarin, a yau DjVu ya kasance ɗaya daga cikin shahararrun nau'ikan nau'ikan ayyukan adabi na “tsare”. Wannan ya faru ne saboda kasancewarsa bude, kuma wasu gazawar fasaha a yau suna ba da damar fasahohin zamani da ci gaba su ketare ta.
A cikin abubuwan da ke gaba za mu ci gaba da labarin game da tarihin bullowar nau'ikan e-littattafai da fasalulluka na aikinsu.
PS da yawa na masu karatun ONYX BOOX:
source: www.habr.com