我知道imagecreatefromgif()、imagecreatefromjpeg() 和imagecreatefrompng()，但是有没有办法从 any 类型的有效图像的 url 创建图像资源（最好是 png）？还是必须先确定文件类型再使用合适的功能？
当我说 url 时，我的意思是 http://sample.com/image.png，而不是数据 url
【问题讨论】：
你分析这段代码。
$url=$_SERVER['REQUEST_URI'];
$url=explode('.',$url);
$extension=$url[1];
switch($extension){
case'jpg':
imagecreatefromjpeg();
break;
}
【讨论】：
$extension 应该是数组的最后一部分，但在您的示例中，它始终是第二部分，如果 $url = "http://www.example.org/images/picture.png" 则 $extension will be "example"。获得最后一部分（你的方式）的正确方法是使用$extension = array_pop(explode('.',$url));。这使$url 保持不变，并从字符串末尾正确提取$extension。
$jpeg_image = imagecreatefromfile( 'photo.jpeg' );
$gif_image = imagecreatefromfile( 'clipart.gif' );
$png_image = imagecreatefromfile( 'transparent_checkerboard.PnG' );
$another_jpeg = imagecreatefromfile( 'picture.JPG' );
// This requires you to remove or rewrite file_exists check:
$jpeg_image = imagecreatefromfile( 'http://example.net/photo.jpeg' );
// SEE BELOW HO TO DO IT WHEN http:// ARGS IS NEEDED:
$jpeg_image = imagecreatefromfile( 'http://example.net/photo.jpeg?foo=hello&bar=world' );
function imagecreatefromfile( $filename ) {
if (!file_exists($filename)) {
throw new InvalidArgumentException('File "'.$filename.'" not found.');
}
switch ( strtolower( pathinfo( $filename, PATHINFO_EXTENSION ))) {
case 'jpeg':
case 'jpg':
return imagecreatefromjpeg($filename);
break;
case 'png':
return imagecreatefrompng($filename);
break;
case 'gif':
return imagecreatefromgif($filename);
break;
default:
throw new InvalidArgumentException('File "'.$filename.'" is not valid jpg, png or gif image.');
break;
}
}
switch 进行一些小修改后，相同的功能就可以用于网址： /* if (!file_exists($filename)) {
throw new InvalidArgumentException('File "'.$filename.'" not found.');
} <== This needs addiotional checks if using non local picture */
switch ( strtolower( array_pop( explode('.', substr($filename, 0, strpos($filename, '?'))))) ) {
case 'jpeg':
之后，您可以将其与http://www.tld/image.jpg 一起使用：
$jpeg_image = imagecreatefromfile( 'http://example.net/photo.jpeg' );
$gif_image = imagecreatefromfile( 'http://www.example.com/art.gif?param=23&another=yes' );
正如您从官方 PHP 手册 function.imagecreatefromjpeg.php 中看到的那样，GD 允许从 function.fopen.php 支持的 URL 加载图像，因此无需先获取图像并将其保存到文件中，并打开该文件。
【讨论】：
首先使用file_get_contents($url) 函数获取url，然后将内容保存到文件中。之后，您可以使用适当的图像处理功能来进一步更改。您可以使用以下代码从 url 保存图像。下面是示例代码：
$url = "http://sample.com/image.png";
$arr = explode("/",$url);
$img_file = dir(__FILE__).'/'.$arr[count($arr)-1];
$data = file_get_contents($url);
$fp = fopen($img_file,"w");
fwrite($fp,$data);
fclose($fp);
谢谢。
【讨论】：
您可能还对最高级的版本感兴趣：
http://salman-w.blogspot.com/2008/10/resize-images-using-phpgd-library.html
<?php
/*
* PHP function to resize an image maintaining aspect ratio
* http://salman-w.blogspot.com/2008/10/resize-images-using-phpgd-library.html
*
* Creates a resized (e.g. thumbnail, small, medium, large)
* version of an image file and saves it as another file
*/
define('THUMBNAIL_IMAGE_MAX_WIDTH', 150);
define('THUMBNAIL_IMAGE_MAX_HEIGHT', 150);
function generate_image_thumbnail($source_image_path, $thumbnail_image_path)
{
list($source_image_width, $source_image_height, $source_image_type) = getimagesize($source_image_path);
switch ($source_image_type) {
case IMAGETYPE_GIF:
$source_gd_image = imagecreatefromgif($source_image_path);
break;
case IMAGETYPE_JPEG:
$source_gd_image = imagecreatefromjpeg($source_image_path);
break;
case IMAGETYPE_PNG:
$source_gd_image = imagecreatefrompng($source_image_path);
break;
}
if ($source_gd_image === false) {
return false;
}
$source_aspect_ratio = $source_image_width / $source_image_height;
$thumbnail_aspect_ratio = THUMBNAIL_IMAGE_MAX_WIDTH / THUMBNAIL_IMAGE_MAX_HEIGHT;
if ($source_image_width <= THUMBNAIL_IMAGE_MAX_WIDTH && $source_image_height <= THUMBNAIL_IMAGE_MAX_HEIGHT) {
$thumbnail_image_width = $source_image_width;
$thumbnail_image_height = $source_image_height;
} elseif ($thumbnail_aspect_ratio > $source_aspect_ratio) {
$thumbnail_image_width = (int) (THUMBNAIL_IMAGE_MAX_HEIGHT * $source_aspect_ratio);
$thumbnail_image_height = THUMBNAIL_IMAGE_MAX_HEIGHT;
} else {
$thumbnail_image_width = THUMBNAIL_IMAGE_MAX_WIDTH;
$thumbnail_image_height = (int) (THUMBNAIL_IMAGE_MAX_WIDTH / $source_aspect_ratio);
}
$thumbnail_gd_image = imagecreatetruecolor($thumbnail_image_width, $thumbnail_image_height);
imagecopyresampled($thumbnail_gd_image, $source_gd_image, 0, 0, 0, 0, $thumbnail_image_width, $thumbnail_image_height, $source_image_width, $source_image_height);
imagejpeg($thumbnail_gd_image, $thumbnail_image_path, 90);
imagedestroy($source_gd_image);
imagedestroy($thumbnail_gd_image);
return true;
}
?>
【讨论】：
我使用这个功能。它支持所有类型的 url 和流包装器以及 php 可以处理的所有图像类型。
/**
* creates a image ressource from file (or url)
*
* @version: 1.1 (2014-05-02)
*
* $param string: $filename url or local path to image file
* @param [bool: $use_include_path] As of PHP 5 the FILE_USE_INCLUDE_PATH constant can be used to trigger include path search.
* @param [resource: $context] A valid context resource created with stream_context_create(). If you don't need to use a custom context, you can skip this parameter by NULL
* @param [&array: $info] Array with result info: $info["image"] = imageinformation from getimagesize, $info["http"] = http_response_headers (if array was populated)
*
* @see: http://php.net/manual/function.file-get-contents.php
* @see: http://php.net/manual/function.getimagesize.php
*
* @return bool|resource<gd> false, wenn aus Dateiinhalt keine gueltige PHP-Bildresource erstellt werden konnte (z.b. bei BMP-Datei)
* @throws InvalidArgumentException Wenn Datei kein gueltiges Bild ist, oder nicht gelesen werden kann
*
*/
function createImageFromFile($filename, $use_include_path = false, $context = null, &$info = null)
{
// try to detect image informations -> info is false if image was not readable or is no php supported image format (a check for "is_readable" or fileextension is no longer needed)
$info = array("image"=>getimagesize($filename));
$info["image"] = getimagesize($filename);
if($info["image"] === false) throw new InvalidArgumentException("\"".$filename."\" is not readable or no php supported format");
else
{
// fetches fileconten from url and creates an image ressource by string data
// if file is not readable or not supportet by imagecreate FALSE will be returnes as $imageRes
$imageRes = imagecreatefromstring(file_get_contents($filename, $use_include_path, $context));
// export $http_response_header to have this info outside of this function
if(isset($http_response_header)) $info["http"] = $http_response_header;
return $imageRes;
}
}
用法（简单示例）：
$image = createImageFromFile("http://sample.com/image.png");
用法（复杂示例）：
// even sources with php extensions are supported and e.g. Proxy connections and other context Options
// see http://php.net/manual/function.stream-context-create.php for examples
$options = array("http"=>
array("proxy" => "tcp://myproxy:8080",
"request_fulluri" => true
)
);
$context = stream_context_create($options);
$image = createImageFromFile("http://de3.php.net/images/logo.php", null, $context,$info);
// ... your code to resize or modify the image
【讨论】：
最简单的方法是让 php 决定文件类型：
$image = imagecreatefromstring(file_get_contents($src));
【讨论】：
这可能对你有帮助
$图像= imagecreatefromstring(file_get_contents('your_image_path_here'));
示例：$image = imagecreatefromstring(file_get_contents('sample.jpg'));
【讨论】：