imagepalettetotruecolor()

(PHP 5 >= 5.5.0, PHP 7)

Converts a palette based image to true color

说明

Converts a palette based image, created by functions like imagecreate() to a true color image, like imagecreatetruecolor().

参数

由图象创建函数(例如imagecreatetruecolor())返回的图象资源。

返回值

Returns TRUE if the convertion was complete, or if the source image already is a true color image, otherwise FALSE is returned.

范例

Converts any image resource to true color

以上例程会输出：

typeof($im) = palette
typeof($im) = true color

参见

• imagecreatetruecolor()新建一个真彩色图像
• imageistruecolor()检查图像是否为真彩色图像

PHP ver 5.4.24 does not support this function (it has not been defined). To get rid of this, you must copy image resource to new image created by function imagecreatetruecolor();
Example with image loaded from GIF file:
$image = imagecreatefromgif("path/to/gif/file.gif"); //create an image from GIF
$width = imagesx($image);               //get width of source image
$height = imagesy($image);               //get height of source image
$image2 = imagecreatetruecolor($width,$height);    //create new image of true colors with given width and height
imagecopy($image2,$image,0,0,0,0,$width,$height);   //copy source image to new one
header("Content-Type: image/jpeg");          //set header for JPG image
imagejpg($image2);                   //render JPg image into browser
imagedestroy($image);                 //free up memory
imagedestroy($image2);

here the working version of walf's solution 

The backwards compatibility example does not preserve transparency. You must first wipe out the default black background on the new image: 

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