note 103146 deleted from function.imagecolorallocatealpha by cmb

Note Submitter: hosh [underscore] 90 [at] live [dot] com ---- I have had a case where I got the alpha from a raw RGBA pallete. This was stored as 8bit where 0 is completely transparant, and 255 is complete opaque. This is impossible to use with imagecolorallocatealpha() as it requires a 7bit int where 0 is completely opaque and 127 is completely transparant (otherway around) You can solve this by subtracting 255, removing the negative sign (either by converting to string and substr($alpha, 1) or some other way) and then bitshifting the answer to the right by one 1 bit. Example: <?php $alpha = 0; // equivalent to alpha 127 needed for imagecolorallocatealpha() $alpha = $alpha - 255; // subtract 255, this will give a negative number $alpha = substr($alpha, 1); // remove negative/minus sign $alpha = (int)$alpha; // convert back to integer $alpha = $alpha >> 1; // bitshift to the right once. echo $alpha; // output: 127 // This can be done in one line of course: $alpha = 255; // equivalent to 0 for imagecolorallocatealpha() $alpha = ((int)(substr($alpha - 255, 1))) >> 1; echo $alpha; // outputs 0 ?>