gd Imagecolortransparent function broken?

Rossy · 03-26-2006, 07:35 PM

hi can someone explain how the Imagecolortransparent() function works exactly? i found this example from the php.net reference but its not making any sense:

PHP Code:


		
			
<?

$image = imagecreatetruecolor(192, 36);

$trans_color = imagecolorallocate($image, 255, 0, 0);

$color = imagecolorallocate($image, 255, 255, 255);

imagecolortransparent($image, $trans_color);

imagettftext($image, 10, 0, 10, 23, $color, "impact.ttf", " MENU ITEM");

imagegif($image, "output.gif");

imagedestroy($image);

?>

Outputs:

the background and text become transparent but the transparent color is red not black or white? i dont get it. i've been asking people everywhere but no one seems to be able to give me an answer. if someone could just make the above code output white text on a transparent background and explain it that would be great

Rossy · 03-26-2006, 09:27 PM

sorry my bad the black background becomes transparent but the transparent color is set to red? the white writing remains opaque which makes sense.

Rossy · 03-26-2006, 11:16 PM

i've actually found out exactly wat the problem is... well atleast i think i have. this is the code i'm using. i'm trying to make the black background transparent.

PHP Code:


		
			
<?
$image = imagecreatetruecolor(192, 36);
$trans_color = imagecolorallocate($image, 0, 0, 0);
$color = imagecolorallocate($image, 255, 255, 255);
imagefill($image, 0, 0, $trans_color);
imagettftext($image, 10, 0, 10, 23, $color, "impact.ttf", " MENU ITEM");
imagecolortransparent($image, $trans_color);
imagegif($image, "output.gif");
?>

aight when i chose the transparent color in its truecolor form (so black [0,0,0]) its pointing to the truecolor index for black which is 0. however when i save it as a gif the palette changes and index 0 in the gif then becomes a different color (its like 20,14,20) or something. hence the transparent property is being passed onto index 0 in the gif and instead of the new black (0,0,0) index being transparent, this other color is. i'll show u an image to demonstrate that there is infact transparency, its just on the wrong color:

you might have to save the image and zoom in on it but theres 1 red pixel there which appeared when i placed the image on top of a red canvas. so yer the transparency is infact working its just pointing to the wrong index in the gif... well thats my theory anyway. does anyone know how to fix this?