note 118389 added to imagick.sigmoidalcontrastimage

The formula for sigmoidal contrast given by Thyssen is missing a term. It should be: ( 1/(1+exp(β*(α-u))) - 1/(1+exp(β*α)) ) / ( 1/(1+exp(β*(α-1))) - 1/(1+exp(β*α)) ) where there was an α missing from the second term. Note that a sigmoidal contrast with α = 6 and β = 0.46 is approximately equivalent to combining a "screen" overlay of the image on itself, followed by a "multiply" overlay. ---- Server IP: 213.172.110.13 Probable Submitter: 89.182.59.197 ---- Manual Page -- http://php.net/manual/en/imagick.sigmoidalcontrastimage.php Edit -- https://master.php.net/note/edit/118389 Del: integrated -- https://master.php.net/note/delete/118389/integrated Del: useless -- https://master.php.net/note/delete/118389/useless Del: bad code -- https://master.php.net/note/delete/118389/bad+code Del: spam -- https://master.php.net/note/delete/118389/spam Del: non-english -- https://master.php.net/note/delete/118389/non-english Del: in docs -- https://master.php.net/note/delete/118389/in+docs Del: other reasons-- https://master.php.net/note/delete/118389 Reject -- https://master.php.net/note/reject/118389 Search -- https://master.php.net/manage/user-notes.php