透明图像的黑色背景

Question

I created an image from other image with the following code,

 imagepng(imagecreatefromstring(file_get_contents(destination path)),source_path);

The image was created,But when i try to create a png image from a transparent image,The background become black color.

Why this happens?How to solve this?

Answer 1

If you look at the GD Documentation you'll find the alpha based functions. Taken directly from imagesavealpha() is the following code that opens a png and outputs it with transparency maintained;

// Load a png image with alpha channels
$png = imagecreatefrompng('./alphachannel_example.png');

// Do required operations
// (So any resizing/rotating/cropping etc)

// Turn off alpha blending and set alpha flag
imagealphablending($png, false);
imagesavealpha($png, true);

// Output image to browser
header('Content-Type: image/png');

imagepng($png);