Translucent Image Reflection in PHP GD

Question

Alright, I've been hacking around with GD Image for a couple of months, and a task that I wanted to accomplish with it was to create a script that takes an existing image, and then creates a reflection that fades out to translucent beneath it.
The following guide shows how to do it with an opaque color : TalkPHP Forums Link

In that forum, Rendair describes a way to overlay a dynamically drawn gradient using a color, with the following PHP code:

    // Next we draw a GD line into our gradient_line
imageline ($gradient_line, 0, 0, $imgName_w, 0, $gdGradientColor);


$i = 0;
$transparency = 30; //from 0 - 100

    while ($i < $gradientHeight) //create line by line changing as we go
    {
        imagecopymerge ($background, $gradient_line, 0,$gradient_y_startpoint, 0, 0, $imgName_w, 1, $transparency);

        ++$i;
        ++$gradient_y_startpoint;

                if ($transparency == 100) {

                    $transparency = 100;

                }
                else 
                {
         // this will determing the height of the
         //reflection. The higher the number, the smaller the reflection. 
         //1 being the lowest(highest reflection)
                    $transparency = $transparency + 1; 

                }

    }

What I'm attempting to accomplish is an effect where we similarly fade each line to one shade more translucent using the alpha feature, but it seems that I have a hard time applying it one line at a time. So far I can only make a tiny slice of the image (one line large) and then overlay it with translucency, I can't seem to fade each line a bit more. So my intended result should be the initial image, then a reflected copy that fades to 100% alpha transparent, but I can't seem to accomplish this.
Any PHP folks out there who have any genius ideas?
Update: this question has earned me the tumbleweed badge.

Answer 1

All right, that was intense. To keep a long story short, imagecopymerge does not properly handle alpha channels. Instead, you need to use imagefilter with the IMG_FILTER_COLORIZE filter to lower the opacity of each line. This code is now part of Image_GD (BSD license). I tried to make the code as clear as possible, but let me know if you have any questions.

Usage using the Kohana Image library works like this:

// Makes a 20px tall reflection with a starting opacity of 100%
// and overwrites the original image with the new one
Image::factory($image_file)->reflection(20, 100)->save();

The really important bits are lines 265-287, which handles the actual line-by-line gradient creation. All instances of $this->width can translate into imagesx($image) (and imagesy for $this->height). $this->_image refers to an GD resource that was created from an existing image.

Oh, and make sure you render the image as a PNG or the gradient alpha will not work properly... :)