{"id":54788,"date":"2020-01-04T00:00:00","date_gmt":"2020-01-03T21:00:00","guid":{"rendered":"https:\/\/prohoster.info\/blog\/blog_prohoster\/jpeg-algoritm-szhatiya"},"modified":"2020-02-18T14:02:50","modified_gmt":"2020-02-18T11:02:50","slug":"jpeg-algoritm-szhatiya","status":"publish","type":"post","link":"https:\/\/prohoster.info\/sq\/blog\/administrirovanie\/jpeg-algoritm-szhatiya","title":{"rendered":"JPEG. Algoritmi i kompresimit","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

P\u00ebrs\u00ebri p\u00ebrsh\u00ebndetje! E kam gjetur k\u00ebt\u00eb artikull t\u00eb shkruar q\u00eb n\u00eb maj 2019. Ky \u00ebsht\u00eb vazhdimi i nj\u00eb serie artikujsh mbi WAVE dhe JPEG. K\u00ebtu e par\u00eb<\/a><\/noindex>. Kjo publikim do t\u00eb p\u00ebrfshij\u00eb informacione n\u00eb lidhje me algoritmin e kodimit t\u00eb imazheve dhe formatin si t\u00eb till\u00eb.<\/p>\n

<\/p>\n

Nj\u00eb doz\u00eb historie<\/h3>\n

<\/p>\n

Nj\u00eb lug\u00eb artikulli nga Wikipedia:<\/p>\n

<\/p>\n

JPEG (Grupi i Ekspert\u00ebve P\u00ebrfotografik) \u00ebsht\u00eb nj\u00eb nga formatet m\u00eb t\u00eb njohura grafike raster, t\u00eb p\u00ebrdorura p\u00ebr ruajtjen e imazheve fotografike dhe imazheve t\u00eb ngjashme.<\/p><\/blockquote>\n

Ky standard \u00ebsht\u00eb zhvilluar nga nj\u00eb grup i bashkuar ekspert\u00ebsh n\u00eb fotografin\u00eb q\u00eb n\u00eb vitin 1991 p\u00ebr kompresimin efikas t\u00eb imazheve.<\/p>\n

<\/a><\/noindex><\/p>\n

Cili \u00ebsht\u00eb rrug\u00ebtimi i imazheve nga forma e pap\u00ebrpunuar n\u00eb JPEG<\/h3>\n

<\/p>\n

Disa mendojn\u00eb se imazhet JPEG jan\u00eb t\u00eb dh\u00ebna t\u00eb pap\u00ebrpunuara t\u00eb kompresuara me metod\u00ebn Huffman, por kjo nuk \u00ebsht\u00eb e v\u00ebrtet\u00eb. Para kompresimit final, t\u00eb dh\u00ebnat kalojn\u00eb nj\u00eb rrug\u00eb t\u00eb gjat\u00eb.<\/p>\n

<\/p>\n

Fillimisht, modeli i ngjyr\u00ebs ndryshohet nga RGB n\u00eb YCbCr. P\u00ebr k\u00ebt\u00eb ka nj\u00eb algorit\u00ebm t\u00eb ve\u00e7ant\u00eb \u2014 k\u00ebtu<\/a><\/noindex>. Y-nuk preket pasi ai \u00ebsht\u00eb p\u00ebrgjegj\u00ebs p\u00ebr ndri\u00e7imin, dhe ndryshimi i tij do t\u00eb jet\u00eb i duksh\u00ebm.<\/p>\n

<\/p>\n

E para q\u00eb b\u00ebhet me imazhin \u00ebsht\u00eb \u00abzakleshtim\u00bb<\/strong> . E kuptoni leht\u00ebsisht: merret nj\u00eb grumbull 2x2 piksel\u00ebsh, dhe pastaj Cb dhe Cr jan\u00eb vlerat mesatare t\u00eb secil\u00ebs nga p\u00ebrb\u00ebr\u00ebsit YCbCr t\u00eb k\u00ebtyre 4 piksel\u00ebve. K\u00ebshtu fituam 6 byte<\/em>, n\u00eb vend t\u00eb 4 Y, 4 Cb, 4 Cr mor\u00ebm 4 Y dhe t\u00eb nj\u00ebjtat p\u00ebr secil\u00ebn prej tyre Cb dhe Cr (4 + 4 + 4 = 12; 4 + 1 + 1 = 6; 12 \u2014 6 = 6). N\u00eb p\u00ebrmasat madje 2\u00d72, kompresimi me humbje me koeficientin e kompresimit 2:1 duket solid. Kjo aplikohet n\u00eb t\u00eb gjith\u00eb imazhin. Dhe k\u00ebshtu \u2014 kemi hequr gjysm\u00ebn e madh\u00ebsis\u00eb. Nj\u00eb teknik\u00eb t\u00eb till\u00eb mund ta p\u00ebrdorim fal\u00eb perceptimit ton\u00eb p\u00ebr ngjyrat. Njeriu me leht\u00ebsi v\u00eb re ndryshimin n\u00eb ndri\u00e7im, por jo n\u00eb ngjyr\u00eb, n\u00ebse ajo \u00ebsht\u00eb e p\u00ebrmbyllur n\u00eb nj\u00eb bllok t\u00eb vog\u00ebl pikselash. Gjithashtu, zakleshtimi mund t\u00eb kryhet n\u00eb nj\u00eb linj\u00eb, 4 piksel\u00eb horizontalisht dhe verticalisht. Varianti i par\u00eb p\u00ebrdoret m\u00eb shpesh. N\u00ebse cil\u00ebsia e imazhit \u00ebsht\u00eb e r\u00ebnd\u00ebsishme, at\u00ebher\u00eb zakleshtimi nuk kryhet fare.
\nIlustrimi vizual i subsampling-ut (Habr nuk dha mund\u00ebsi t\u00eb ngarkohej nj\u00eb gif) \u2014 https:\/\/i.ibb.co\/Rg5Th9H\/150953010617579181.gif<\/a><\/noindex><\/p>\n

<\/p>\n

Pjesa kryesore e p\u00ebrgatitjes<\/h5>\n

\nDCP<\/p>\n

Tani pjesa m\u00eb e nd\u00ebrlikuar dhe e domosdoshme. Imazhi ndahen n\u00eb blloqe 8\u00d78 (p\u00ebrdoren mbushje n\u00eb rast se p\u00ebrmasat nuk jan\u00eb t\u00eb shumta me an\u00ebn e bllokut).<\/p>\n

<\/p>\n

Tani \u00e7do bllok i n\u00ebnshtrohet DCP (Transformimi Diskret i Kosinuseve)<\/strong>. N\u00eb k\u00ebt\u00eb pjes\u00eb t\u00eb imazhit hiqet gjith\u00e7ka e tep\u00ebrt. Duke p\u00ebrdorur DCP duhen kuptuar n\u00ebse ky bllok (8\u00d78) p\u00ebrshkruan ndonj\u00eb pjes\u00eb monotone t\u00eb imazhit: qielli, muret; apo ai p\u00ebrmban nj\u00eb struktur\u00eb komplekse (flok\u00eb, simbole, etj.). Logjikisht, 64 piksel\u00eb t\u00eb ngjash\u00ebm me ngjyr\u00eb mund t\u00eb p\u00ebrshkruhen me vet\u00ebm 1, pasi madh\u00ebsia e bllokut \u00ebsht\u00eb tashm\u00eb e njohur. Ja ku \u00ebsht\u00eb dhe kompresimi: 64 me 1.<\/p>\n

<\/p>\n

DCP e kthen bllokun n\u00eb spektrin, dhe atje ku treguesit ndahen menj\u00ebher\u00eb, koeficienti b\u00ebhet pozitiv, dhe sa m\u00eb sharp t\u00eb jet\u00eb kalimi, aq m\u00eb i lart\u00eb do t\u00eb jet\u00eb rezultati. Atje ku koeficienti \u00ebsht\u00eb m\u00eb i lart\u00eb, n\u00eb imazh jan\u00eb pasqyruar kalime t\u00eb qarta t\u00eb ngjyr\u00ebs dhe ndri\u00e7imit, ku ai \u00ebsht\u00eb m\u00eb i ul\u00ebt \u2014 nd\u00ebrrime t\u00eb dob\u00ebta (t\u00eb qet\u00eb) t\u00eb vlerave t\u00eb p\u00ebrb\u00ebr\u00ebsve YCbCr n\u00eb bllok.<\/p>\n

\nKuantimi<\/p>\n

K\u00ebtu tashm\u00eb aplikohet konfigurimi i kompresimit. \u00c7do koeficient n\u00eb secil\u00ebn nga matrica 8\u00d78 ndahet me nj\u00eb num\u00ebr t\u00eb caktuar. N\u00ebse cil\u00ebsia e imazhit pas t\u00eb gjitha modifikimeve nuk do t\u00eb ulet m\u00eb, at\u00ebher\u00eb ndarja duhet t\u00eb jet\u00eb nj\u00eb. N\u00ebse ju intereson m\u00eb shum\u00eb memoria q\u00eb z\u00eb kjo fotografi, at\u00ebher\u00eb ndarja do t\u00eb jet\u00eb m\u00eb e madhe se 1, dhe rezultati rroundohet. K\u00ebshtu, pas rroundimit shpesh ka shum\u00eb zero.<\/p>\n

<\/p>\n

Kuantimi b\u00ebhet p\u00ebr t\u00eb krijuar mund\u00ebsi p\u00ebr kompresim edhe m\u00eb t\u00eb madh. K\u00ebshtu duket shembulli i kuantimit t\u00eb grafik\u00ebs y = sin(x):<\/p>\n

<\/p>\n

\"JPEG.<\/p>\n

\nKomprimi<\/p>\n

Fillimisht kalojm\u00eb p\u00ebrmes matric\u00ebs zig-zag:<\/p>\n

<\/p>\n

\"JPEG.<\/p>\n

<\/p>\n

Marrim nj\u00eb varg t\u00eb vet\u00ebm me numra. Shohim se ka shum\u00eb zero, ato mund t\u00eb hiqen. P\u00ebr k\u00ebt\u00eb, n\u00eb vend t\u00eb nj\u00eb sekuence me shum\u00eb zero vendosim 1 zero dhe pas tij numrin q\u00eb tregon sasin\u00eb e tyre n\u00eb sekuenc\u00eb. K\u00ebshtu, mund t\u00eb ulim deri n\u00eb 1\/3 t\u00eb madh\u00ebsis\u00eb s\u00eb gjith\u00eb vargut. M\u00eb pas, thjesht e kompresojm\u00eb k\u00ebt\u00eb varg me metod\u00ebn e Huffman-it dhe e shkruajm\u00eb n\u00eb vet\u00eb skedarin.<\/p>\n

<\/p>\n

Ku p\u00ebrdoret<\/h3>\n

<\/p>\n

Kudo. Si dhe PNG, JPEG p\u00ebrdoret n\u00eb aparate fotografike, OS\u2019je (si logot e kompanive, ikonat e aplikacioneve, thumbnail\u2019e) dhe n\u00eb t\u00eb gjitha fushat e mundshme ku \u00ebsht\u00eb e nevojshme t\u00eb ruhen efektivisht imazhet.<\/p>\n

<\/p>\n

P\u00ebrfundim<\/h3>\n

<\/p>\n

Aktualisht, njohurit\u00eb mbi JPEG jan\u00eb t\u00eb vlefshme vet\u00ebm p\u00ebr q\u00ebllime edukative, sepse ato jan\u00eb tashm\u00eb t\u00eb integruara kudo dhe optimizuar nga grupe t\u00eb m\u00ebdha njer\u00ebzish, megjithat\u00eb, shkenca \u00ebsht\u00eb akoma nj\u00eb gj\u00eb e k\u00ebndshme.<\/p>\n

\nBurimet<\/p>\n

Artikulli mbi YCbCr n\u00eb Wikipedia<\/a><\/noindex>
\nArtikulli mbi JPEG n\u00eb Wikipedia<\/a><\/noindex>
\nPak mbi DCP nga postimi n\u00eb Pikabu<\/a><\/noindex>
\nArtikulli mbi DCP n\u00eb Wikipedia<\/a><\/noindex><\/p>\n

Burimi: habr.com<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

\u0418 \u0441\u043d\u043e\u0432\u0430 \u0437\u0434\u0440\u0430\u0432\u0441\u0442\u0432\u0443\u0439\u0442\u0435! \u042f \u043d\u0430\u0448\u0435\u043b \u044d\u0442\u0443 \u0441\u0442\u0430\u0442\u044c\u044e, \u043d\u0430\u043f\u0438\u0441\u0430\u043d\u043d\u0443\u044e \u0435\u0449\u0435 \u043c\u0430\u0435 2019-\u043e\u0433\u043e \u0433\u043e\u0434\u0430. \u042d\u0442\u043e \u2014 \u043f\u0440\u043e\u0434\u043e\u043b\u0436\u0435\u043d\u0438\u0435 \u0441\u0435\u0440\u0438\u0438 \u0441\u0442\u0430\u0442\u0435\u0439 \u043e WAVE \u0438 JPEG, \u0412\u043e\u0442 \u043f\u0435\u0440\u0432\u0430\u044f. \u042d\u0442\u0430 \u043f\u0443\u0431\u043b\u0438\u043a\u0430\u0446\u0438\u044f \u0432\u043a\u043b\u044e\u0447\u0438\u0442 \u0432 \u0441\u0435\u0431\u0435 \u0438\u043d\u0444\u043e\u0440\u043c\u0430\u0446\u0438\u044e \u043e\u0431 \u0430\u043b\u0433\u043e\u0440\u0438\u0442\u043c\u0435 \u043a\u043e\u0434\u0438\u0440\u043e\u0432\u0430\u043d\u0438\u044f \u0438\u0437\u043e\u0431\u0440\u0430\u0436\u0435\u043d\u0438\u0439 \u0438 \u043e \u0441\u0430\u043c\u043e\u043c \u0444\u043e\u0440\u043c\u0430\u0442\u0435 \u0432 \u0446\u0435\u043b\u043e\u043c. \u0429\u0435\u043f\u043e\u0442\u043a\u0443 \u0438\u0441\u0442\u043e\u0440\u0438\u0438 \u0421\u0442\u043e\u043b\u043e\u0432\u0443\u044e \u043b\u043e\u0436\u043a\u0443 \u0441\u0442\u0430\u0442\u044c\u0438 \u0438\u0437 \u0412\u0438\u043a\u0438\u043f\u0435\u0434\u0438\u0438: JPEG (Joint Photographic Experts Group) \u2014 \u043e\u0434\u0438\u043d \u0438\u0437 \u043f\u043e\u043f\u0443\u043b\u044f\u0440\u043d\u044b\u0445 […]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[688],"tags":[],"class_list":["post-54788","post","type-post","status-publish","format-standard","hentry","category-administrirovanie"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\n","aioseo_head_json":{"title":"\ud83e\udd47JPEG. 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