PHP GD 庫圖像處理函數完整分類速查表（含實戰封裝建議）

前言

GD 庫是 PHP 內建圖形處理擴展，函數超百個。本文按功能分類整理常用函數，並給出面向對象封裝建議，作為開發速查手冊。

1. 圖像創建與載入

2. 圖像複製與縮放

3. 繪圖基元

4. 文字繪製

5. 顏色管理

6. 圖像屬性獲取

7. 輸出與銷毀

8. 進階特效（PHP 5.5+ / 7+）

• imagefilter($im, IMG_FILTER_GRAYSCALE) - 灰度
• imagefilter($im, IMG_FILTER_GAUSSIAN_BLUR) - 高斯模糊
• imagefilter($im, IMG_FILTER_SELECTIVE_BLUR) - 選擇性模糊
• imagefilter($im, IMG_FILTER_EMBOSS) - 浮雕
• imagefilter($im, IMG_FILTER_MEAN_REMOVAL) - 邊緣檢測
• imagefilter($im, IMG_FILTER_SMOOTH, $weight) - 平滑
• imageconvolution($im, $matrix, $div, $offset) - 自定義卷積核（銳化、邊緣增強等）

面向對象封裝建議：ImageManager 類

class ImageManager {
    private $im;
    private $width, $height;

    public static function create(int $w, int $h, bool $trueColor = true): self {
        $instance = new self();
        $instance->im = $trueColor ? imagecreatetruecolor($w, $h) : imagecreate($w, $h);
        $instance->width = $w; $instance->height = $h;
        return $instance;
    }

    public static function load(string $path): self {
        $info = getimagesize($path);
        $func = ['', 'imagecreatefromgif', 'imagecreatefromjpeg', 'imagecreatefrompng'][$info[2]] ?? null;
        if (!$func) throw new Exception("Unsupported format");
        $instance = new self();
        $instance->im = $func($path);
        $instance->width = $info[0]; $instance->height = $info[1];
        return $instance;
    }

    public function color(int $r, int $g, int $b, int $alpha = 0): int {
        return $alpha ? imagecolorallocatealpha($this->im, $r, $g, $b, $alpha)
                      : imagecolorallocate($this->im, $r, $g, $b);
    }

    public function text(string $text, string $font, int $size, int $x, int $y, int $color, int $angle = 0): self {
        imagettftext($this->im, $size, $angle, $x, $y, $color, $font, $text);
        return $this;
    }

    public function rect(int $x1, int $y1, int $x2, int $y2, int $color, bool $fill = false): self {
        $fill ? imagefilledrectangle($this->im, $x1, $y1, $x2, $y2, $color)
              : imagerectangle($this->im, $x1, $y1, $x2, $y2, $color);
        return $this;
    }

    public function save(string $path, int $quality = 90): bool {
        $ext = strtolower(pathinfo($path, PATHINFO_EXTENSION));
        $func = ['jpg'=>'imagejpeg', 'jpeg'=>'imagejpeg', 'png'=>'imagepng', 'gif'=>'imagegif'][$ext] ?? null;
        if (!$func) throw new Exception("Unsupported save format");
        return $func($this->im, $path, $quality);
    }

    public function output(int $quality = 90): void {
        header('Content-Type: ' . image_type_to_mime_type(IMAGETYPE_PNG));
        imagepng($this->im, null, $quality);
    }

    public function __destruct() {
        if ($this->im) imagedestroy($this->im);
    }
}

// 使用
$img = ImageManager::create(200, 100);
$red = $img->color(255, 0, 0);
$white = $img->color(255, 255, 255);
$img->rect(0, 0, 199, 99, $red, true)
    ->text('Hello GD', 'font.ttf', 24, 20, 60, $white)
    ->save('output.png');

結語

GD 函數雖多，但核心常用約 30 個。掌握「創建→繪製/文字→輸出→銷毀」流程，配合 ImageManager 鏈式調用，即可優雅完成驗證碼、海報生成、圖表繪製等需求。複雜矢量/濾鏡場景建議改用 ImageMagick (Imagick 擴展)。