{"id":8985,"date":"2022-09-16T15:24:35","date_gmt":"2022-09-16T09:54:35","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-question-about-setting-opacity-property\/"},"modified":"2022-09-16T15:24:35","modified_gmt":"2022-09-16T09:54:35","slug":"solved-question-about-setting-opacity-property","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-question-about-setting-opacity-property\/","title":{"rendered":"[Solved] question about setting ‘opacity’ property"},"content":{"rendered":"

[ad_1]
\n<\/p>\n

\n
\n
<\/div>\n
\n
\n

I managed to solve the example to get the SCREEN color of div2:
\nfirst we apply the simple alpha compositing formula:<\/p>\n

\n

co = Cs x as + Cb x ab x (1 – as) ; ao = as + ab (1-as)<\/p>\n<\/blockquote>\n

here :
\n{div2} Cs = (100\/255, 200\/255, 50\/255) ; as = 0.5
\n{div1} Cb = (22\/255, 177\/255, 200\/255) ; ab = 0.4
\n….<\/p>\n

co = ( 0.213 , 0.53 , 0.25 )
\nao = 0.7<\/p>\n

NOW WE APPLY the opacity. In my example I set it to 0.7 , (it’s the same value as the result of ao but it’s a coincidence)<\/strong>
and that’s what I was looking for: how to apply opacity in color calculation formulas<\/strong><\/p>\n

\n

co = co * 0.7
\nao = ao * 0.7<\/p>\n<\/blockquote>\n

In my question I gave the link:
https:\/\/www.w3.org\/TR\/css-color-3\/#transparency<\/a>
\nand an excerpt from the passage that I did not understand
\non this site:<\/p>\n

“If the object has children, then the effect is as if the children were blended against the current background using a mask where the value of each pixel of the mask is alphavalue”<\/em><\/p>\n

i understand now the : “using a mask” means doing this : multiply RGBA,( co and ao), by opacity<\/p>\n

\n

co = ( 0.213 * 0.7<\/strong> , 0.53 * 0.7<\/strong> , 0.25 * 0.7<\/strong> ) ; ao = 0.7 * 0.7<\/strong>
\nco= (0.15, 0.37, 0.18)
\nao = 0.49<\/p>\n

the rest is the calculation of the color obtained after “opacity” on the background :<\/p>\n

We compose with the color of the background:
\n(note co is premultiplied<\/strong><\/em>, so we apply :<\/p>\n

\n

= Cs + Cb * ab * (1-as)
\nCs is the color calculated previously (premultiplied) : (0.15 0.37
\n0.18)
\nCb is the background color (77\/255 , 100\/255 , 150\/255) ab=1
\n= ( 0.30 , 0.57 , 0.48 )<\/p>\n<\/blockquote>\n

a screenshot of div2 gives the same color<\/strong><\/p>\n<\/p><\/div>\n

<\/div>\n<\/div>\n

<\/span> <\/p><\/div>\n<\/div>\n

[ad_2]<\/p>\n

solved question about setting ‘opacity’ property <\/p>\n","protected":false},"excerpt":{"rendered":"

[ad_1] I managed to solve the example to get the SCREEN color of div2: first we apply the simple alpha compositing formula: co = Cs x as + Cb x ab x (1 – as) ; ao = as + ab (1-as) here : {div2} Cs = (100\/255, 200\/255, 50\/255) ; as = 0.5 {div1} … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[464],"class_list":["post-8985","post","type-post","status-publish","format-standard","hentry","category-solved","tag-css"],"yoast_head":"\n[Solved] question about setting 'opacity' property - JassWeb<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jassweb.com\/solved\/solved-question-about-setting-opacity-property\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] question about setting 'opacity' property - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] I managed to solve the example to get the SCREEN color of div2: first we apply the simple alpha compositing formula: co = Cs x as + Cb x ab x (1 – as) ; ao = as + ab (1-as) here : {div2} Cs = (100\/255, 200\/255, 50\/255) ; as = 0.5 {div1} ... 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