{"action":"closed","issue":{"url":"https://api.github.com/repos/nodeca/pica/issues/22","labels_url":"https://api.github.com/repos/nodeca/pica/issues/22/labels{/name}","comments_url":"https://api.github.com/repos/nodeca/pica/issues/22/comments","events_url":"https://api.github.com/repos/nodeca/pica/issues/22/events","html_url":"https://github.com/nodeca/pica/issues/22","id":91721331,"number":22,"title":"Understanding Unsharp algorithm ","user":{"login":"jardakotesovec","id":1590681,"avatar_url":"https://avatars.githubusercontent.com/u/1590681?v=3","gravatar_id":"","url":"https://api.github.com/users/jardakotesovec","html_url":"https://github.com/jardakotesovec","followers_url":"https://api.github.com/users/jardakotesovec/followers","following_url":"https://api.github.com/users/jardakotesovec/following{/other_user}","gists_url":"https://api.github.com/users/jardakotesovec/gists{/gist_id}","starred_url":"https://api.github.com/users/jardakotesovec/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/jardakotesovec/subscriptions","organizations_url":"https://api.github.com/users/jardakotesovec/orgs","repos_url":"https://api.github.com/users/jardakotesovec/repos","events_url":"https://api.github.com/users/jardakotesovec/events{/privacy}","received_events_url":"https://api.github.com/users/jardakotesovec/received_events","type":"User","site_admin":false},"labels":[],"state":"closed","locked":false,"assignee":null,"milestone":null,"comments":1,"created_at":"2015-06-29T07:20:04Z","updated_at":"2015-07-05T13:22:14Z","closed_at":"2015-07-05T13:22:14Z","body":"Hi,\r\njust looking into your unsharp algorithm and I got lost in last step. Could you explain me one thing.\r\nI assume that you implement this formula `USM(O) = O + (2 * (Amount / 100) * (O - GB))`, right?\r\n\r\nWhat puzzle me is that you are using multiplication [`(c * corr)`](https://github.com/nodeca/pica/blob/master/lib/pure/unsharp.js#L76) for the correction and not addition as the formula above suggests. Is that intention? Maybe its some optimization that I don't understand :-).\r\n\r\nThank you for hint!"}}