How to make an Image to show only black text - php

Question

I am trying to do the following:
I Have a picture I want to make that only text which is written in black remains visible and rest of every colour gets transparent.
I tried to do this using PHP imagecolortransparent function but I am not able to figure out how to make it work.
Any help will be great.
Thanks In advance

Answer 1

Updated Answer
There must be an easier way, but until I think of it, this should work:
// Read original image
$start = imagecreatefrompng("input.png");
// Make true colour image same size
$im = imagecreatetruecolor(imagesx($start),imagesy($start));
$transparent = imagecolorallocatealpha($im, 0, 0, 0, 127);
$red=imagecolorallocate($im,255,0,0);
imagesavealpha($im, TRUE);
// Fill the new image with transparency
imagefill($im, 0, 0, $transparent);
// Copy only black pixels across from original to new
for($x=0;$x<imagesx($im);$x++){
for($y=0;$y<imagesy($im);$y++){
$rgb = imagecolorat($start,$x,$y);
if($rgb==0){
imagesetpixel($im,$x,$y,$black);
}
}
}
imagepng($im,"result.png");
Original Answer
I would do this:
// Read original image
$start = imagecreatefrompng("input.png");
// Create a proper truecolour image the same size that can support transparency
$im = imagecreatetruecolor(imagesx($start),imagesy($start));
$transparent = imagecolorallocatealpha($im, 0, 0, 0, 127);
imagefill($im, 0, 0, $transparent);
imagesavealpha($im, TRUE);
$black = imagecolorallocate($im, 0, 0, 0);
$text="This is some quite black text";
imagestring($im,5,0,75,$text,$black);
imagepng($im,"result.png");
input.png
result.png