PHP 图像处理实战 GD/Imagick 从入门到精通，构建高性能图像服务 ​

<?php
function loadImage(string $path): array {
    if (!is_readable($path)) throw new RuntimeException("Not readable: $path");

    $info = @getimagesize($path);
    if (!$info) throw new RuntimeException("Not an image: $path");
    [$w, $h] = $info;
    $mime = $info['mime'] ?? '';
    if ($w * $h > 50_000_000) { // ~50 MP 保护
        throw new RuntimeException("Too large: {$w}x{$h}");
    }
    switch ($mime) {
        case 'image/jpeg': $img = imagecreatefromjpeg($path); break;
        case 'image/png':  $img = imagecreatefrompng($path);  break;
        case 'image/webp': $img = function_exists('imagecreatefromwebp') ? imagecreatefromwebp($path) : null; break;
        default: throw new RuntimeException("Unsupported type: $mime");
    }
    if (!$img) throw new RuntimeException("Failed to load: $path");
    // 修复 EXIF 方向（JPEG）
    if ($mime === 'image/jpeg' && function_exists('exif_read_data')) {
        $exif = @exif_read_data($path);
        $orientation = (int)($exif['Orientation'] ?? 1);
        $img = orientGd($img, $orientation);
    }
    // 确保 PNG/WebP 的透明度
    if ($mime === 'image/png' || $mime === 'image/webp') {
        imagesavealpha($img, true);
        imagealphablending($img, false);
    }
    return [$img, $mime, $w, $h];
}

function orientGd(\GdImage $img, int $o): \GdImage {
    switch ($o) {
        case 3:  return imagerotate($img, 180, 0);
        case 6:  return imagerotate($img, -90, 0);
        case 8:  return imagerotate($img, 90, 0);
        case 2:  imageflip($img, IMG_FLIP_HORIZONTAL); return $img;
        case 4:  imageflip($img, IMG_FLIP_VERTICAL);   return $img;
        case 5:  $r = imagerotate($img, -90, 0); imageflip($r, IMG_FLIP_HORIZONTAL); return $r;
        case 7:  $r = imagerotate($img, 90, 0);  imageflip($r, IMG_FLIP_HORIZONTAL); return $r;
        default: return $img;
    }
}

function resizeCover(\GdImage $src, int $tw, int $th, float $fx=0.5, float $fy=0.5): \GdImage {
    $sw = imagesx($src); $sh = imagesy($src);
    $scale = max($tw / $sw, $th / $sh);
    $cw = (int)ceil($tw / $scale);
    $ch = (int)ceil($th / $scale);

    $sx = (int)max(0, min($sw - $cw, $fx * $sw - $cw / 2));
    $sy = (int)max(0, min($sh - $ch, $fy * $sh - $ch / 2));
    $dst = imagecreatetruecolor($tw, $th);
    imagesavealpha($dst, true);
    $transparent = imagecolorallocatealpha($dst, 0, 0, 0, 127);
    imagefill($dst, 0, 0, $transparent);
    imagealphablending($dst, false);
    imagecopyresampled($dst, $src, 0, 0, $sx, $sy, $tw, $th, $cw, $ch);
    return $dst;
}

function resizeContain(\GdImage $src, int $tw, int $th, ?array $bg=null): \GdImage {
    $sw = imagesx($src); $sh = imagesy($src);
    $scale = min($tw / $sw, $th / $sh, 1.0);
    $nw = max(1, (int)floor($sw * $scale));
    $nh = max(1, (int)floor($sh * $scale));
    $dx = (int)floor(($tw - $nw) / 2);
    $dy = (int)floor(($th - $nh) / 2);
    $dst = imagecreatetruecolor($tw, $th);
    if ($bg === null) {
        imagesavealpha($dst, true);
        $transparent = imagecolorallocatealpha($dst, 0, 0, 0, 127);
        imagefill($dst, 0, 0, $transparent);
        imagealphablending($dst, false);
    } else {
        [$r,$g,$b] = $bg;
        $color = imagecolorallocate($dst, $r, $g, $b);
        imagefill($dst, 0, 0, $color);
    }
    imagecopyresampled($dst, $src, $dx, $dy, 0, 0, $nw, $nh, $sw, $sh);
    return $dst;
}

function saveOptimized(\GdImage $img, string $dest, string $format, array $opts=[]): void {
    $f = strtolower($format);
    if ($f === 'avif' && function_exists('imageavif')) {
        $q = $opts['quality'] ?? 80;
        if (!imageavif($img, $dest, $q)) throw new RuntimeException("Failed AVIF: $dest");
        return;
    }
    if ($f === 'webp' && function_exists('imagewebp')) {
        $q = $opts['quality'] ?? 80;
        imagesavealpha($img, true);
        if (!imagewebp($img, $dest, $q)) throw new RuntimeException("Failed WebP: $dest");
        return;
    }
    if ($f === 'png') {
        $level = $opts['compression'] ?? 6;
        imagesavealpha($img, true);
        if (!imagepng($img, $dest, $level)) throw new RuntimeException("Failed PNG: $dest");
        return;
    }
    // JPEG 格式回退（启用渐进式加载）
    $q = max(60, min(90, (int)($opts['quality'] ?? 82)));
    imageinterlace($img, true);
    if (!imagejpeg($img, $dest, $q)) throw new RuntimeException("Failed JPEG: $dest");
}

[$img] = loadImage(__DIR__.'/uploads/user123.jpg');
$thumb = resizeCover($img, 256, 256);
saveOptimized($thumb, __DIR__.'/public/avatars/user123.webp', 'webp', ['quality'=>82]);

[$img] = loadImage(__DIR__.'/uploads/sku-42.png');
$thumb = resizeContain($img, 600, 400, [255,255,255]);
saveOptimized($thumb, __DIR__.'/public/thumbs/sku-42.jpg', 'jpeg', ['quality'=>80]);

<?php
function imagickCover(string $in, int $tw, int $th, string $out, string $format, array $opts=[]): void {
    $im = new Imagick($in);
    $im->setIteratorIndex(0);
    $im->autoOrient(); // 处理 EXIF 方向信息
    $im->cropThumbnailImage($tw, $th); // Cover 模式裁剪，使用高质量滤镜
    $fmt = strtolower($format);
    $im->stripImage(); // 删除元数据以减小文件大小
    if ($fmt === 'jpeg' || $fmt === 'jpg') {
        $im->setImageFormat('jpeg');
        $im->setImageCompressionQuality($opts['quality'] ?? 82);
        $im->setInterlaceScheme(Imagick::INTERLACE_PLANE);
    } elseif ($fmt === 'webp') {
        $im->setImageFormat('webp');
        $im->setOption('webp:method', (string)($opts['method'] ?? 6)); // 压缩方法，范围 0-6
        $im->setImageCompressionQuality($opts['quality'] ?? 80);
    } elseif ($fmt === 'avif') {
        $im->setImageFormat('avif');
        $im->setImageCompressionQuality($opts['quality'] ?? 45);
    } else {
        $im->setImageFormat($fmt); // PNG 等其他格式
    }
    if (!$im->writeImage($out)) throw new RuntimeException("Failed to write: $out");
    $im->clear(); $im->destroy();
}

function imagickContain(string $in, int $tw, int $th, string $out, string $format, string $bg='white'): void {
    $im = new Imagick($in);
    $im->autoOrient();
    $im->thumbnailImage($tw, $th, true); // 等比例缩放
    $canvas = new Imagick(); $canvas->newImage($tw, $th, $bg);
    $x = (int)(($tw - $im->getImageWidth())/2);
    $y = (int)(($th - $im->getImageHeight())/2);
    $canvas->compositeImage($im, Imagick::COMPOSITE_OVER, $x, $y);
    $canvas->stripImage();
    $canvas->setImageFormat($format);
    $canvas->writeImage($out);
    $canvas->destroy(); $im->destroy();
}

<?php
// /public/image.php?src=uploads/hero.jpg&w=1600&h=900&fit=cover&fmt=webp&q=80
declare(strict_types=1);
require __DIR__.'/image_helpers.php'; // 引入上面定义的辅助函数

$src = realpath(__DIR__.'/'.($_GET['src'] ?? '')) ?: '';
if ($src === '' || !str_starts_with($src, realpath(__DIR__))) {
    http_response_code(400); exit('Bad src');
}
$w   = max(1, (int)($_GET['w'] ?? 800));
$h   = max(1, (int)($_GET['h'] ?? 600));
$fit = $_GET['fit'] ?? 'cover'; // 适配模式：cover 或 contain
$fmt = strtolower($_GET['fmt'] ?? 'webp');
$q   = (int)($_GET['q'] ?? 82);
$cacheKey = sha1("$src|$w|$h|$fit|$fmt|$q");
$cacheDir = __DIR__.'/cache';
$outPath  = "$cacheDir/$cacheKey.$fmt";

if (!is_dir($cacheDir)) mkdir($cacheDir, 0775, true);

if (!file_exists($outPath)) {
    [$img] = loadImage($src);
    $dst = ($fit === 'contain') ? resizeContain($img, $w, $h) : resizeCover($img, $w, $h);
    saveOptimized($dst, $outPath, $fmt, ['quality'=>$q]);
}

// 设置 HTTP 缓存头
$mtime = filemtime($outPath);
$etag = '"' . md5($cacheKey . $mtime) . '"';
header('ETag: '.$etag);
header('Cache-Control: public, max-age=31536000, immutable');
header('Last-Modified: '.gmdate('D, d M Y H:i:s', $mtime).' GMT');
if (@strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE'] ?? '') >= $mtime ||
    trim($_SERVER['HTTP_IF_NONE_MATCH'] ?? '') === $etag) {
    http_response_code(304); exit;
}

$mime = ['jpg'=>'image/jpeg','jpeg'=>'image/jpeg','png'=>'image/png','webp'=>'image/webp','avif'=>'image/avif'][$fmt] ?? 'application/octet-stream';
header('Content-Type: '.$mime);
readfile($outPath);

$start = microtime(true);
$before = filesize($srcPath);
// ... 图像处理逻辑 ...
$after = filesize($outPath);
$ms = (microtime(true) - $start) * 1000;
$peakMb = memory_get_peak_usage(true) / (1024*1024);
error_log(json_encode([
    'op'=>'resize-cover','src_bytes'=>$before,'dst_bytes'=>$after,
    'saved'=>$before - $after,'ms'=>round($ms),'peak_mb'=>round($peakMb,1)
]));