问题:

I am taking a PNG image from a url as below.
I want to convert the PNG image to JPEG without saving disk with PHP.

Finally I want to assign JPEG image to $content_jpg variable.

 $url = 'http://www.example.com/image.png';
 $content_png = file_get_contents($url);

 $content_jpg=;

回答1:

You want to use the gd library for this. Here's an example which will take a png image and output a jpeg one. If the image is transparent, the transparency will be rendered as white instead.

<?php

$file = "myimage.png";

$image = imagecreatefrompng($file);
$bg = imagecreatetruecolor(imagesx($image), imagesy($image));

imagefill($bg, 0, 0, imagecolorallocate($bg, 255, 255, 255));
imagealphablending($bg, TRUE);
imagecopy($bg, $image, 0, 0, 0, 0, imagesx($image), imagesy($image));
imagedestroy($image);

header('Content-Type: image/jpeg');

$quality = 50;
imagejpeg($bg);
imagedestroy($bg);

?>

回答2:

Simplified answer is,

// PNG image url
$url = 'http://www.example.com/image.png';

// Create image from web image url
$image = imagecreatefrompng($url);

// Start output buffer
ob_start(); 

// Convert image
imagejpeg($image, NULL,100);
imagedestroy($image);

// Assign JPEG image content from output buffer
$content_jpg = ob_get_clean();