问PHP提供的图像总是损坏

EN

$imgpath = 'assets/img/dropdown-arrow.png';
$type      = pathinfo($imgpath, PATHINFO_EXTENSION);
$data      = file_get_contents($imgpath);
$base64    = 'data:image/' . $type . ';base64,' . base64_encode($data);
header('Content-Type: image/png;'); // also tried with charset=UTF-8 and such
echo base64_decode($base64);
exit();

// Set the content type header - in this case image/png
header('Content-Type: image/png; charset=UTF-8');
// integer representation of the color black (rgb: 0,0,0)
$background = imagecolorallocate($img, 0, 0, 0);

// removing the black from the placeholder
imagecolortransparent($img, $background);

// turning off alpha blending (to ensure alpha channel information
// is preserved, rather than removed (blending with the rest of the
// image in the form of black))
imagealphablending($img, false);

// turning on alpha channel information saving (to ensure the full range
// of transparency is preserved)
imagesavealpha($img, true);

// Output the image
imagepng($img);