note 82162 added to function.imagefilter

Function to change the transparency of a png image on the fly. Works only with PNG, and with a browser supporting alpha channel. The function stretches the opacity-range of the image, so that the most opaque pixel(s) will be set to the given opacity. (Other opacity values in pixels are modified accordingly.) Returns success or failure. <?php function filter_opacity( &$img, $opacity ) //params: image resource id, opacity in percentage (eg. 80) { if( !isset( $opacity ) ) { return false; } $opacity /= 100; //get image width and height $w = imagesx( $img ); $h = imagesy( $img ); //turn alpha blending off imagealphablending( $img, false ); //find the most opaque pixel in the image (the one with the smallest alpha value) $minalpha = 127; for( $x = 0; $x < $w; $x++ ) for( $y = 0; $y < $h; $y++ ) { $alpha = ( imagecolorat( $img, $x, $y ) >> 24 ) & 0xFF; if( $alpha < $minalpha ) { $minalpha = $alpha; } } //loop through image pixels and modify alpha for each for( $x = 0; $x < $w; $x++ ) { for( $y = 0; $y < $h; $y++ ) { //get current alpha value (represents the TANSPARENCY!) $colorxy = imagecolorat( $img, $x, $y ); $alpha = ( $colorxy >> 24 ) & 0xFF; //calculate new alpha if( $minalpha !== 127 ) { $alpha = 127 + 127 * $opacity * ( $alpha - 127 ) / ( 127 - $minalpha ); } else { $alpha += 127 * $opacity; } //get the color index with new alpha $alphacolorxy = imagecolorallocatealpha( $img, ( $colorxy >> 16 ) & 0xFF, ( $colorxy >> 8 ) & 0xFF, $colorxy & 0xFF, $alpha ); //set pixel with the new color + opacity if( !imagesetpixel( $img, $x, $y, $alphacolorxy ) ) { return false; } } } return true; } ?> Example for use: <?php $image = imagecreatefrompng( "img.png" ); filter_opacity( $image, 75 ); header( "content-type: image/png" ); imagepng( $image ); imagedestroy( $image ); ?> ---- Server IP: 69.147.83.197 Probable Submitter: 77.234.81.252 ---- Manual Page -- http://www.php.net/manual/en/function.imagefilter.php Edit -- https://master.php.net/note/edit/82162 Del: integrated -- https://master.php.net/note/delete/82162/integrated Del: useless -- https://master.php.net/note/delete/82162/useless Del: bad code -- https://master.php.net/note/delete/82162/bad+code Del: spam -- https://master.php.net/note/delete/82162/spam Del: non-english -- https://master.php.net/note/delete/82162/non-english Del: in docs -- https://master.php.net/note/delete/82162/in+docs Del: other reasons-- https://master.php.net/note/delete/82162 Reject -- https://master.php.net/note/reject/82162 Search -- https://master.php.net/manage/user-notes.php