Code to change colour image to black & white

Is there any code I can use to change a colour image on a web page to a black & white one, without having to have 2 of the same images on our server?

 

Here are some examples:
www.php.net/imagecopymergegray

 

<?php
// The file you are grayscaling
$file = 'yourfile.jpg';

// This sets it to a .jpg, but you can change this to png or gif if that is what you are working with
header('Content-type: image/jpeg');

// Get the dimensions
list($width, $height) = getimagesize($file);

// Define our source image
$source = imagecreatefromjpeg($file);

// Creating the Canvas
$bwimage= imagecreate($width, $height);

//Creates the 256 color palette
for ($c=0;$c<256;$c++)
{
$palette[$c] = imagecolorallocate($bwimage,$c,$c,$c);
}

//Creates yiq function
function yiq($r,$g,$b)
{
return (($r*0.299)+($g*0.587)+($b*0.114));
}

//Reads the origonal colors pixel by pixel
for ($y=0;$y<$height;$y++)
{
for ($x=0;$x<$width;$x++)
{
$rgb = imagecolorat($source,$x,$y);
$r = ($rgb >> 16) & 0xFF;
$g = ($rgb >> 8) & 0xFF;
$b = $rgb & 0xFF;

//This is where we actually use yiq to modify our rbg values, and then convert them to our grayscale palette
$gs = yiq($r,$g,$b);
imagesetpixel($bwimage,$x,$y,$palette[$gs]);
}
}

// Outputs a jpg image, but you can change this to png or gif if that is what you are working with
imagejpeg($bwimage);
?>

PHP:

Got this from here.
http://php.about.com/od/gdlibrary/ss/grayscale_gd.htm

 

Thanks guys, very helpful. I will try to get this going on my site now.

 

So, as an example, where or how would I put the code in a page like this?
http://www.photosales.co.nz/details.php?gid=62&pid=5050
It would be nice to have a button for people to click to view as greyscale.

 

I am going to use this in a job.

Thanks