除了使用imagejpeg或imagepng之外，还有更高质量的将PHP图像资源转换为jpeg或png的方法吗？

Question

Currently I am using imagepng to convert an image resource based off of an original image to an png image type. This proved to have a higher level of quality than the imagejpeg function was creating for my jpg.

However you can clearly see that the compression algorithms in these two functions are not of as high quality as one that would be in something like Photoshop.

Does anyone know of a way to get a higher quality jpeg? Is there documentation on the format of the image resource and how it is converted to a jpeg or png? If I had that information I could at least try to implement a better algorithm.

//Create image
        $im = apppic($filename, $colors);
        imagepng($im, "images/app/".rtrim($path_array[$count],"jpeg")."png", 0);

function promopic ($filename, $colors){


    if(@imagecreatefromjpeg($filename))
            $img = imagecreatefromjpeg($filename);
    elseif(@imagecreatefrompng($filename))
            $img = imagecreatefrompng($filename);
    elseif(@imagecreatefromgif($filename))
            $img = imagecreatefromgif($filename);
    $width = imagesx($img);
    $height = imagesy($img);
    $imHeight = 625;

    if( $width/$height > 4/5){$imWidth = 800; $imHeight = $height/$width*$imWidth ; }
    else {  $imWidth = $width/$height*$imHeight;  }

    $colorWidth = 1200 - $imWidth;
    $numColors = count($colors);
    $colorHeight = ceil($imHeight/$numColors) - 2;
    $imHeight = ceil($imHeight/$numColors)* $numColors - 2;


    $im = @imagecreate(1200, $imHeight+50)
        or die("Cannot Initialize new GD image stream");
    $background_color = imagecolorallocate($im, 250, 250, 250);
    $text_color = imagecolorallocate($im, 255, 255, 251);
    $blue_color = imagecolorallocate($im, 40, 5, 251);


    //Add color boxes
    for ($i = 1; $i <= $numColors; $i++) {
        $imcolorbox = @imagecreate($colorWidth, $colorHeight);
        $rgb = hex2rgb($colors[($i-1)]);

        $colorbox_color = imagecolorallocate($imcolorbox, $rgb[0], $rgb[1], $rgb[2]);
        $dest_x = 1200-$colorWidth;
        $dest_y = ($colorHeight + 2) * ($i-1);

        $copy_image = imagecopy($im, $imcolorbox,  $dest_x, $dest_y, 0, 0, $colorWidth, $colorHeight);
        imagedestroy($imcolorbox);
        //imagestring($im, 5, 1075, 2+$dest_y,  "Reinvogue.com", $text_color);
        //imagestring($im, 5, $imWidth+5, 2+$dest_y,  "Reinvogue.com", $text_color);
        //imagestring($im, 5, 1050, 17+$dest_y,  "Hex: ".$colors[($i-1)], $text_color);
        //imagestring($im, 5, 1050, 2+$dest_y,  "RGB: ".$rgb[0]." ".$rgb[1]." ".$rgb[2], $text_color);
    }

     imagestring($im, 5, 10, $imHeight+15,  "Powered by the Reinvogue.com Colorway Engine", $blue_color);


    $copy_image = imagecopyresampled($im, $img,  0, 0, 0, 0, $imWidth-2, $imHeight, $width, $height);
    return $im;
}

Answer 1

This should create a high quality image with a white background:

$im = @imagecreatetruecolor(1200, $imHeight+50)
$white = imagecolorallocate($im, 255, 255, 255);
imagefill($im, 0, 0, $white);

If you're working with png images you can even have a look at imagecolorallocatealpha ( http://www.php.net/manual/en/function.imagecolorallocatealpha.php )

Hope this helps.

Answer 2

For high-quality PNG8 use pngquant2 . PHP's built-in libgd fork has awful palette conversion.

Quoting: http://pngquant.org/php.html

<?php

/**
 * 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 http://pngquant.org
 *
 * @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;
}