imagecreatefromstring()

(PHP 4 >= 4.0.4, PHP 5, PHP 7)

从字符串中的图像流新建一图像

说明

imagecreatefromstring()返回一个图像标识符，其表达了从给定字符串得来的图像。图像格式将自动检测，只要 PHP 支持：JPEG，PNG，GIF，WBMP 和 GD2。

参数

A string containing the image data.

返回值

An image resource will be returned on success.FALSE is returned if the image type is unsupported, the data is not in a recognised format, or the image is corrupt and cannot be loaded.

范例

imagecreatefromstring() example

以上例程的输出类似于：

参见

• imagecreatefromjpeg()由文件或 URL 创建一个新图象。
• imagecreatefrompng()由文件或 URL 创建一个新图象。
• imagecreatefromgif()由文件或 URL 创建一个新图象。
• imagecreatetruecolor()新建一个真彩色图像

While downloading images from internet, it's easiest to let php decide what is the file type. So, forget using imagecreatefromjpg, imagecreatefromgif and imagecreatefrompng. Instead, this is the way to go: 

My site allows anonymous uploads to a web-accessible location (that will execute a script if it finds one).
Naturally, I need to verify that only harmless content is accepted. I am expecting only images, so I use: 

[Editor's note: BMP will be supported as of PHP 7.2.0.]
In case it's not obvious from the lack of "imagecreatefrombmp()" in GD, this function cannot handle plain old BMP files either.

So you guys don't spend an hour trying to figure out why your script keeps running out of memory when you're using this or the other imagecreatefrom functions. GD uncompresses the image when you use these functions, and this can lead to your script running out of memory.
If you download a rawimage save it on your computer to jpeg so the file size comes down, GD will automatically convert it to the raw and you can possibly run out of memory.

An easy example to help understanding this function...

The function will try to auto-determine file format (jpg, gif, png....), and will return false if fails.

imagecreatefromstring does not appear to support WebP images (tested on PHP 7.2.10, with GD 2.1.0 and GD WebP support enabled)

Many websites add, during the conversion from .jpg / .png to base64 some words before the base64 string : "data:image/png;base64,"
If you let them, the PHP function will return an error "Data is not in a recognized format in".
If you have this situation : 
$image_string=str_replace("data:image/png;base64,","",$image_string);
$image_string = base64_decode($image_string);
$img = imagecreatefromstring($image_string);

I know a lot of people have been having trouble using images from the Sprint PPC6700 with GD. The jpeg library always thows an error about 16 bytes of extraneous data. I decided to poke around in a hex editor and found those extraneous bytes occur right at the end of the exif data.
By removing this extraneous data, images can easily be manipulated by GD and the EXIF extension as a normal images. This also removes any problems using the images with GIMP which must rely on the same jpeg libraries.
Here is a function that will check to see if an image is from the PPC6700 and then remove the extraneous data for you. The result can successully be used with imagecreatefromstring
Author: Paul Visco
IM: paulsidekick
Created: 2-12-06
function checkFixPPC6700($orig){
  //get the file contents
  $data = file_get_contents($orig);
  //if its a PPC 6700 image cut out the extraneous 16 bits
  if(strstr($data, "\x41\x70\x61\x63\x68\x65\x00\x48")){
//this next line can all be one string I split it up so the form on php.net would accept it
    $bad_data ="\x00\x10\x4A\x46" . "\x49\x46\x00\x01\x01" . "\x00\x00\x01\x00\x01\x00\x00";
    return substr_replace($data, "", strpos($data, $bad_data),
    strlen($bad_data));
  } else {
    //if not from a PPC 6700 return data unaltered
     return $data;
  }
}

Generating graphs in an external program (in this case, gnuplot) may cause problems. This is a solution hacked together in the late hours of night.

[/PHP]

Here is the code I did to create a thumbnail image from the database blob field. The trick is to use "imagecreatefromstring()" to create an image file.
Jack Shieh 

I found out that in PHP 4.3.2 and 4.3.4 that the 'imagecreatefromstring' function use a lot of memory when working with big image...
Try this piece of code with a big image (like 1Meg or more)

With a 400k image. I run with a 16M Mem_limit but for a 1.4M image, the mem_limit required jump to more that 32M

I'm trying to get the imagecreatefromstring to work with GIFs. Of course, it won't.
I've read the tips but can't get them to work either.
The following is what I tried, based on above tips:
---
  header('Content-Type: image/gif');
  header('Content-Disposition: inline; filename=file.gif');
  $temp = tmpfile();
  fwrite($temp, $line['image']);
  $src_img = imagecreatefromgif($temp);
  fclose($temp); // this removes the file
  $dst_img = imagecreatetruecolor(100, 100);
  imagecopyresampled($dst_img, $src_img, 0,0,0,0, 100,100, imagesx($src_img), imagesy($src_img));
  
  imagegif($dst_img);
---
where $line['image'] is the gif as taken from my MySQL database...
If anyone that has been able to make something like this work could give me a working piece of code I'd be really greatful!
I would be great if the tempfile could be excluded too...
Below is a working piece of code for jpeg:
---
  header('Content-Type: image/jpeg');
  header('Content-Disposition: inline; filename=file.jpg');
  
  $src_img = imagecreatefromstring($line['image']);
  $dst_img = imagecreatetruecolor(100, 100);
  imagecopyresampled($dst_img, $src_img, 0,0,0,0, 100,100, imagesx($src_img), imagesy($src_img));
  
  imagejpeg($dst_img);

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