Using pngquant in PHP

The following compress_png() function will take a path to a PNG file and return file contents of a compressed file. It reduces file size and preserves transparency! This is how TinyPNG, Kraken, and other such services work, so you can build your own.

Copy the function and run it like in examples below.


 * Optimizes PNG file with pngquant 1.8 or later (reduces file size of 24-bit/32-bit PNG images).
 * You need to install pngquant 1.8 on the server (ancient version 1.0 won't work).
 * There's package for Debian/Ubuntu and RPM for other distributions on
 * @param $path_to_png_file string - path to any PNG file, e.g. $_FILE['file']['tmp_name']
 * @param $max_quality int - conversion quality, useful values from 60 to 100 (smaller number = smaller file)
 * @return string - content of PNG file after conversion
function compress_png($path_to_png_file, $max_quality = 90)
    if (!file_exists($path_to_png_file)) {
        throw new Exception("File does not exist: $path_to_png_file");

    // guarantee that quality won't be worse than that.
    $min_quality = 60;

    // '-' makes it use stdout, required to save to $compressed_png_content variable
    // '<' makes it read from the given file path
    // escapeshellarg() makes this safe to use with any path
    $compressed_png_content = shell_exec("pngquant --quality=$min_quality-$max_quality - < ".escapeshellarg(    $path_to_png_file));

    if (!$compressed_png_content) {
        throw new Exception("Conversion to compressed PNG failed. Is pngquant 1.8+ installed on the server?");

    return $compressed_png_content;


Compress uploaded PNG file

You can compress a PNG file when it's uploaded: (remember to change name in $_FILE[] and $save_to_path)

$read_from_path = $_FILE['file']['tmp_name'];
$save_to_path = "uploads/compressed_file.png";

$compressed_png_content = compress_png($read_from_path);
file_put_contents($save_to_path, $compressed_png_content);

// you don't need move_uploaded_file(). file_put_contents() will do that instead.

Convert PNG files on the fly

You optimize PNG files that are already on disk:

$path_to_uncompressed_file = 'test.png';
$path_to_compressed_file = 'test-small.png';

// this will ensure that $path_to_compressed_file points to compressed file
// and avoid re-compressing if it's been done already
if (!file_exists($path_to_compressed_file)) {
    file_put_contents($path_to_compressed_file, compress_png($path_to_uncompressed_file));

// and now, for example, you can output the compressed file:
header("Content-Type: image/png");
header('Content-Length: '.filesize($path_to_compressed_file));

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