Decoding a canvas todataURL

I’m having difficulty using data created with canvas’s todataurl() method. Currently my code sends the resulting data to my php server which uses the file_put_contents() method to create a file to store that data. Now if I cut and paste the resulting gibberish from the file into an image tag src it works fine and displays properly so I assume so far everything is peachy.

But I keep running into issues when I try to use the code in JS. I’ve tried php’s base64_decode method but kept getting currupt files. I found this code:

<?php
  $encodedData = str_replace(' ','+',$encodedData);
  $decocedData = base64_decode($encodedData);

and still got currupted files. Ideally I’d like to create a .png file with it but I’d settle for just processing the data file again in JS. Any help greatly appreciated.

Here is Solutions:

We have many solutions to this problem, But we recommend you to use the first solution because it is tested & true solution that will 100% work for you.

Solution 1

It seems you have to get rid of the header that is prepended to the image data by the toDataURL() function.
On the client side you can strip off the header like this:

..
var data=canvas.toDataURL();
var output=data.replace(/^data:image\/(png|jpg);base64,/, "");
// now send "output" to the server
..

On the server side use this:

<?php
    $decocedData = base64_decode($encodedData);
?>

Solution 2

In java script send the result from canvas.toDataURL() on those browsers than support this method with the default type of “image/png”.

var imageInfo = canvas.toDataURL();
// now send "imageInfo" to the server

Direct way to create the png file:

<?php
$imageInfo = imageInfoFromBrowser(); // Your method to get the data
$image = fopen($imageInfo, 'r');
file_put_contents("fileName.png", $image);
fclose($image);
?>

I have this working in PHP 5.3 / Windows, for other version, please check.

Image data sample for testing on PHP.

$imageInfo = "data:image/png;base64,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"

Solution 3

Another important note is you have to convert blanks into plusses. If you do not do that, the decoded data is corrupted:

$encodedData = str_replace(' ','+',$encodedData);
$decocedData = base64_decode($encodedData);

You can read more at http://www.php.net/manual/en/function.base64-decode.php

Solution 4

Other solutions did not work for me.

This works:

//image sample
$baseFromJavascript = "data:image/png;base64,BBBFBfj42Pj4";

// remove the part that we don't need from the provided image and decode it
$data = base64_decode(preg_replace('#^data:image/\w+;base64,#i', '', $baseFromJavascript));

Note: Use and implement solution 1 because this method fully tested our system.
Thank you 🙂

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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