Converting array bit into actual image

Question

I have an array bit like this:

[255, 216, 255, 224, 0, 16, 74, 70, 73, 70, 0, 1, 1, 0, 0, 1, 0, 1, 0, 0, 255, 219, 0, 67, 0, 1, 1, ...]

And I need to convert this into an actual image.

So I followed this python script that does the same and works properly:

file = x['data']['file']['file'] 

listRes = file.replace(' ', '')
listRes = listRes.replace('[', '').replace(']', '')
listRes = listRes.split(',')
for i in range(len(listRes)):
    listRes[i] = int(listRes[i])
f = open('x.png', 'wb')
f.write(bytes(listRes))
f.close()

And this is my similar php code:

if(!empty($que["answer"]["file"])){
    $strbit = str_replace("[","",$que["answer"]["file"]["file"]);
    $strbit = str_replace("]","",$strbit);
    $strbit = str_replace(" ","",$strbit);
    $arrbit = explode(',', $strbit);
    for($j=0;$j<count($arrbit);$j++){
        $arrbit[$j] = (int)($arrbit[$j]);
    }
    $imageName = str_random(10).'.'.'png';
    \File::put(storage_path(). '/images/' . $imageName, ($arrbit));
}

But now the problem is that the exported image looks like this:

Now instead of \File::put(storage_path()... I tried using file_put_contents($imageName, pack("C*", ...$arrbit)); but it does not export anything at all!

So what's going wrong here? How can I solve this issue?

UPDATE #1:

I tried this:

if(!empty($que["answer"]["file"])){
        $strbit = str_replace("[","",$que["answer"]["file"]["file"]);
        $strbit = str_replace("]","",$strbit);
        $strbit = str_replace(" ","",$strbit);
        $arrbit = explode(',', $strbit);
        for($j=0;$j<count($arrbit);$j++){
            $arrbit[$j] = (int)($arrbit[$j]);
        }
        $imageName = str_random(10).'.'.'jpeg';
        file_put_contents($imageName, pack("C*", ...$arrbit));
    }

But does not export any image and also not return any error!

You remove commas, while Python code splits string into array of numeric strings by comma. As to how write it to the disk, see the first answer to this question. — alx
– alx, Commented Sep 5, 2022 at 8:39
I dont see the python code doing any base64 decoding, and the python code is saving as a mp4 and you're saving as a png — Dale
– Dale, Commented Sep 5, 2022 at 8:57
@alx I have updated the question would you mind check it out — Peter Amo
– Peter Amo, Commented Sep 5, 2022 at 9:30
@Dale I have updated the question would you mind check it out — Peter Amo
– Peter Amo, Commented Sep 5, 2022 at 9:31
In your last line of php code try this \File::put(storage_path(). '/images' . $imageName, (implode('', $arrbit))); I suspect if you open the file in a text editor you will the word Array — Dale
– Dale, Commented Sep 5, 2022 at 9:35

alx · Accepted Answer · 2022-09-05 13:35:21Z

2

+50

So, main issue was: how to convert input format -- string of comma separated character codes in brackets -- into binary form and write it to the file.

PHP has pack() function which fits this purpose nicely. Specifically, we need C* format as we are going to output raw 8-bit characters. So, given we have this input:

$arr = [255, 216, 255, 224, 0, 16, 74, 70, 73, 70, 0, 1, 1, 0, 0, 1, 0, 1, 0, 0, 255, 219, 0, 67, 0, 1, 1, /* ... */];

This is how we can convert it into a binary string (note the ... token -- it is very important here, as pack() expects one argument per character converted, not an array as a single argument):

$str = pack("C*", ...$arr);

Finally, original question was asking about .png files, but apparently the example data has JFIF header, which indicates .jpg format. If format is not known, one can use getimagesize() to guess it (note: the function requires file already written to disk, not a binary string with file contents).

answered Sep 5, 2022 at 13:35

alx

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2 Comments

Peter Amo Over a year ago

Thanks once again, but one more question: does this work on .mp4 video files also?

alx Over a year ago

Yes, should work for any binary file.

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