shell_exec输出到变量的pngquant

Question

我试图使用以下代码(来源)对PHP使用pngquant：

<?php 


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

    // maybe with more memory ?
    ini_set("memory_limit", "128M");

    // The command should look like: pngquant --quality=60-90 - < "image-original.png"
    $comm = "pngquant --quality=$min_quality-$max_quality - < ".escapeshellarg(    $path_to_png_file);

    $compressed_png_content = shell_exec($comm);

    var_dump($compressed_png_content);

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

    return $compressed_png_content;
}

echo compress_png("image-original.png");

函数应该检索shell_exec函数的输出。通过输出，我应该能够创建一个新的png文件，但是浏览器中shell_exec的输出是损坏的：�PNG。

注意：命令的执行是在控制台中成功地执行的，而没有pngquant --quality=60-90 - < "image-original.png" (pngquant --quality=60-90 - < "image-original.png")

如果我从控制台执行php代码，将得到以下消息：

错误:将图像写入标准输出失败(16)

我到处找都找不到解决办法，有人能帮我吗，或者知道是什么导致了这个问题？

Answer 1

将php-pngquant包装器允许从PNGQuant生成的图像中直接检索到变量使用getRawOutput方法中。

<?php 

use ourcodeworld\PNGQuant\PNGQuant;

$instance = new PNGQuant();

$result = $instance
    ->setImage("/image/to-compress.png")
    ->setQuality(50,80)
    ->getRawOutput();

// Result is an array with the following structure
// $result = array(
//    'statusCode' => 0,
//    'tempFile' => "/tmp/example-temporal.png",
//    'imageData' => [String] (use the imagecreatefromstring function to get the binary data)
//)

// Get the binary data of the image
$imageData = imagecreatefromstring($result["imageData"]);

// Save the PNG Image from the raw data into a file or do whatever you want.
imagepng($imageData , '/result_image.png');

在遮罩下，包装器在PNGQuant中提供一个临时文件作为输出参数，然后pngquant将压缩的图像写入该文件，并在结果数组中检索其内容。您仍然可以使用结果数组的PNGQuant索引验证statusCode的退出代码。