Esli ti sobiraeshsja zhit' i rabotat' po-Eninski, to est' tak kak nam zaveshal Velikii, to what is alfa channel MUST know.
Esli ti pozvolish sebe takuju shalost' i potratish neskolko chasov pitajas' razobrat'sja "chto takoe alpha channel" i "kak on rabotaet", to vsem, navernoe, na Zemle stanet nemozhechko luchshe...
Dabi zainteresovat' tebja nemnogo teoriei 2d images..ja vkratce popitajus' opisat to - bez ponimanija chego voobshe, kak ja schitaju, nel'zja vkljuchat' pristavat' k simpotichnim devchonkam...
Esli ti otkroesh , skazhem, Photoshop...to ti uvidesh chto kazhdii image sostoit po-krainei mere iz treh channel...odin Red, drugoi - Gree...nu i poslednii - Blue - to bish sinii po nashenski... Eto tri channels imejut tolko 256 ottenkov -ot belogo to chernogo...esli ti sprosish ljubogo liftera v svoem dome "pochemu tolko 256" to on tebe srazu zhe otvetit, chto tak kak na odin channel otvedeno bilo lish 8 bits...a mi znaem chto 8 bits mogut sozdat tolko 2 v 8 stepeni variacii - to bish 256...eto kstati pochemu ti chasto vidish v 2d image processing software info on image: chto to vrode" 24 bits image"...-vse verno tri channela po 8 bits (256 ottenkov na channel) - poluchaem 24 bita. Tut ti pereb'ezh vozmushenno svoego liftera "Kak zhe tak! esli vse tri channela cherno belie- kak zhe konechnii image - cvetnoei?" ..."A tak zhe!" - otvetir Lifter...:V shkole uchitsja nado bilo!"...no potom uspokoevshis' Lifter prodolzhit: "...2d Software processes white values of the channel as "full of the color " i posilaet na computernii display skazhem -krasnii pizel...esli mi govorim o Red channel white value...a vse drugie channeli imejut chernie znachenie dannogo pixela na ekrane...razumeesh?...i mi ved' znaem..chto RGB -est' PRIMARY COLORS- to bish OSNOVNIE...chto eto znachit na praktike? -a to chto etimi tremja cvetami mi mozhem opisat' ljuboi drugoi ti vstrachaesh vokrug zhivjan a belom svete...(po-krainei mere millioni)..nadejus' chto ti dochital do etoi tochki..esli prochital, to uzhe ne ostaavlivaisja- ved' mi pochti u finala...
Nu tak vot...Ja uzhe skazal chto tolko 256 ottenkov na cvetovoi channel..ot 0 -255 gde 0 is black i 255 full color -to est' "white". Inache govorja - kazhdii pixel na kratinke imeet tri znachenija - odin po Red, drugoi po Blue i po Green..Predstav' image kak kollekciju PIXELOV S TREMJA ZNACHENIJAMI. ZAPOMNI ETO. ljuboi image eto prezhde vsego set of the pixels with three RGB value from 0 to 255.
Pixel znachenie ne mozhet bit' menshe chem 0 i bolshe chem 255. Eto zakon dzhunglei i net puti obmanut' software. Esli ti umnozhish zanchenie kazhdogo pixela na 0 to ves' image stanet "BLACK" tak kak umnozhenie ljubogo chisla na 0 est' nol'. Esli ti k kazhdomu pixelu dobavish kakoe libo znachenie i resultirueshee znachenie budet bol'she chem 255. to "cropping will occure" na znachenii 255 ...to bish...esli original znachenie pixela bolo 155...i ti dobavil k nemu znachenie 180 to resultat dolzhen bit 335...no chto sluchitsja -t o chto software prosto "crop" ego na znachenii 255 - to bish white - to est "full color".
Vsja etamatematika privedennaja vishe kasaetsja kazhdogo channela...Skazhem ti beresh pervii image (set of the pixels with rgb values) i hochesh nalozhit na nego drugoi image sverhu...
Posmotri chto sluchitsja: na primere tolko odnogo pixela (hotja kazhdii pixel budet zadeistvovan)...voz'mem verhnii levie pixel kazhdogo image...predpolozhim chto razmer (resolution oboih odinakov)..pixel value pervogo image ravno R= 10 G= 80 B=255
...pixel value vtorogo image ravno R=30 G= 150 B= 40...Predpolozhim chto daniie pixeli etih images posle nakladki sovpodut. Esli ti eto delaesh v fotoshope...to by default verhii image zakroet nizhnii...to est' photoshop prosto ignariruet values pervogo pixela...chto vi sdelat kakuju libo matematicheskuju kombinaciju tebe neobhodimo vobrat' Screen Mode - po suti dela eto matematicheskie operanti...davai rassmotrim operant "Add"..tak kak on i zvichit -danii operant budet dobavljat' znachenie pervogo pixela ko vtromu...chto sluchitsja v dannom primere?...R= 10 + 30 G = 80 + 150 B= 255 + 40 to est' R= 40 G= 230 B= 295. No znachenie pixela ne mozhet bit' bolshe chem 255 to bish result is :
R= 40 G= 230 B=255. Te zhe zakoni rassprostronjajutsja i na Multiply i na Screen, i na drugie "Modes" - to bish matematisheskie operanti....
Teper o Alpha channel...alpha channel eto chetvertii Channel RGB image...chto on delaet? da ni chego..poka ti ne nachnesh combinirovat' image s alpha channel s drugim image..chto sluchitsja- prosto kazhdii value of the pixela budet UMNOZHENO NA VALUE PIXELA OF THE ALPHA CHANNELA...a image kotorii pod nim...budet umnozhen na INVERTED ALPHA CHANELi zatem oba imagesRGB channels budut combinirovani kak "ADD mode" to est' "+"
Esli value of the pixel of alpha channel bilo "black" , to posle multiply etot black value of alpha pixel na value red, green blue pixels (otdel'no), to result budet BLACK ili "0" - nol')
Teper alpha pixel value budet inverted - to bish stanet White - "1" -edenica. To est' eto znachit chto posle multiplying the pixel value vtorogo image pixel value NE izmenitsja tak kak multiplying chislo na 1 = resultat ne izmenjaetsja...Teper image budut combinirovanni ispol'zuja ADD + matematicheskii operand. tak kak pixel value pervogo image bilo chem to..no tak kak ono bilo umnozheno na black value of the alpha channel to bish umnozheno na 0...to est' stalo NOL' -to est' "MASKED" ...i teper value budut combinirovani ..to et' k nulju budet dobavleno kak mi znaem neizmenennoe snachenie vtorogo image...vot tebe i ves' trick..i vsja concepcija 2d image processing...
Esli ti poimesh kak etot mechanizm rabotaet na pixel value -to mnogoe stanet ponjatno i jasno..
Nadejus' chto bilo veselo i smeshno
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