6

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.

joel
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  • You simply have to read the MIME type (probably fixed/known) and the encoding (probably none) to interpret the data, which is standard Base64. There won’t be any spaces to be replaced if you URL-encoded the input earlier. [PHP-FileUpload](https://github.com/delight-im/PHP-FileUpload) has a [`DataUriUpload`](https://github.com/delight-im/PHP-FileUpload/blob/023f812226673ac9e0696d8a3579bb7380606dda/src/DataUriUpload.php) component which does all this automatically. It’s documented [here](https://github.com/delight-im/PHP-FileUpload/tree/023f812226673ac9e0696d8a3579bb7380606dda#data-uri-uploads). – caw Dec 04 '17 at 23:41

4 Answers4

15

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);
?>
stewe
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    That was helpful, here is what I ended up doing if anyone needs to do the same in the future: $backGround = substr($backGround, 22); $backGround = str_replace(' ','+',$backGround); $backGround = base64_decode($backGround); file_put_contents("currentBG1.png", $backGround); – joel Sep 03 '11 at 05:33
  • need to add jpeg to the regular expression as well: var output=data.replace(/^data:image\/(png|jpg|jpeg);base64,/, ""); – dickyj Mar 20 '15 at 08:21
3

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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"
Daniel De León
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  • If this fail for you, please post your PHP environment. Thanks. – Daniel De León May 22 '12 at 16:35
  • canvas.toDataUrl()... what is this ? – realtebo Jan 21 '14 at 12:07
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    `canvas.toDataUrl()` is used for example on [fabric.js](http://fabricjs.com/). You can get your canvas via JavaScript `var imageInfo = document.getElementById("yourid").toDataURL();` or via JQuery `var imageInfo = $("#yourid").toDataURL();` This solution posted by @DanielDeLeón works like a charm. Thank you, – ptCoder May 04 '15 at 12:42
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    I think this should be higher. Seems like the proper way to do it. – Ace7k3 Oct 25 '17 at 20:05
2

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

hiddentstones
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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));
lost in binary
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