PHP GD: How to get imagedata as binary string?

Question

I'm using a solution for assembling image files to a zip and streaming it to browser/Flex application. (ZipStream by Paul Duncan, http://pablotron.org/software/zipstream-php/).

Just loading the image files and compressing them works fine. Here's the core for compressing a file:

// Reading the file and converting to string data
$stringdata = file_get_contents($imagefile);

// Compressing the string data
$zdata = gzdeflate($stringdata );

My problem is that I want to process the image using GD before compressing it. Therefore I need a solution for converting the image data (imagecreatefrompng) to string data format:

// Reading the file as GD image data
$imagedata = imagecreatefrompng($imagefile);
// Do some GD processing: Adding watermarks etc. No problem here...

// HOW TO DO THIS??? 
// convert the $imagedata to $stringdata - PROBLEM!

// Compressing the string data
$zdata = gzdeflate($stringdata );

Any clues?

spoulson · Accepted Answer · 2009-07-31 15:15:27Z

52

One way is to tell GD to output the image, then use PHP buffering to capture it to a string:

$imagedata = imagecreatefrompng($imagefile);
ob_start();
imagepng($imagedata);
$stringdata = ob_get_contents(); // read from buffer
ob_end_clean(); // delete buffer
$zdata = gzdeflate($stringdata);

edited Jul 31, 2009 at 15:15

answered Jul 30, 2009 at 14:22

spoulson

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1 Comment

supersan Over a year ago

I tried this and for some reason it fails with nested ob_start. I found M.i.X's answer below to be a better solution.

M.i.X · Accepted Answer · 2019-12-30 02:36:37Z

26

The php://memory stream can be used when output-buffer juggling is unwanted. https://www.php.net/manual/en/wrappers.php.php

$imagedata = imagecreatefrompng($imagefile);

// processing

$stream = fopen('php://memory','r+');
imagepng($imagedata,$stream);
rewind($stream);
$stringdata = stream_get_contents($stream);

// Compressing the string data
$zdata = gzdeflate($stringdata );

answered Dec 30, 2019 at 2:36

M.i.X

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3 Comments

supersan Over a year ago

This is a much better answer than ob_start() hackery. Thanks!

Tom Over a year ago

Not sure why but this doesn't work on Windows under PHP 5.6.18. "10 is not a valid stream resource"

Karol Pawlak Over a year ago

Beautiful way. Much better than using ob_*

Stefan Brinkmann · Accepted Answer · 2013-04-09 18:20:50Z

23

// ob_clean(); // optional
ob_start();
imagepng($imagedata);
$image = ob_get_clean();

answered Apr 9, 2013 at 18:20

Stefan Brinkmann

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1 Comment

Kenneth Vogt Over a year ago

ob_get_clean() essentially executes both ob_get_contents() and ob_end_clean(), so this solution is slightly more elegant that the accepted answer above.

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