php：//输入令人困惑的数组信息

I have a base64 text, which is huge, posted from Ajax. In console, I can see the code, and if i copy and paste it into a base64 image converter it works fine.

In PHP $_POST is always empty, but php://input shows all the information, which is a JSON with four parts within the array. Under the 'imgData' part, the image binary code is complete and works, but if I do this:

 $data = json_decode(file_get_contents('php://input'));
(A) print_r($data); // Shows all the image data under [imgData]

(B) print_r($data->imgData); //  Only shows a small part of the image data

Here is an example of the output (A):

stdClass Object
(
    [switch] => addImage
    [table] => tbl_images
    [propid] => 
    [imgData] => data:image/jpeg;base64,iVBORw0KGgoAAAANSUhEUgAAAPoAAAD6CAYAAACI7Fo9AAAAHGlET1QAAAACAAAAAAAAAH0AAAAoAAAA 

Here is the exmaple output (B):

data:image/jpeg;base64,iVBORw0KGgoAAAANSUhEUgAAAPoAAAD6CAYAAACI7Fo9AAAAHGlET1QAAAACAA

But (B) is only part of the data? Any reason for this ?

UPDATE

$data = json_decode(file_get_contents('php://input'));
(A) var_dump($data);

(B) var_dump($data->imgData); 

The above are now equal and give the same string sizes.

When I put this into a SQL query:

        $detail = "Property_Id, Image_Data ) VALUES ( 213, " . $data->imgData;

        $sql = "INSERT INTO " . $table . " ( " . $detail . " )";
        echo $sql;
        $addQ = $mysqli->query($sql);

        echo 'image added';

        print_r($mysqli->error);
    } else {
        echo "No params added";
    }

It still does not show the end of the $sql string ?