PHP怎样实现图片缩略图生成？GD库应用实例

phpinfo()

<?php

// 原图路径
$source_image = 'path/to/your/image.jpg';

// 缩略图保存路径
$thumb_image = 'path/to/your/thumb.jpg';

// 缩略图宽度和高度
$thumb_width = 200;
$thumb_height = 150;

// 获取原图尺寸
list($source_width, $source_height, $source_type) = getimagesize($source_image);

// 根据原图类型创建图像资源
switch ($source_type) {
    case IMAGETYPE_JPEG:
        $source = imagecreatefromjpeg($source_image);
        break;
    case IMAGETYPE_PNG:
        $source = imagecreatefrompng($source_image);
        break;
    case IMAGETYPE_GIF:
        $source = imagecreatefromgif($source_image);
        break;
    default:
        die('不支持的图片类型');
}

// 创建缩略图资源
$thumb = imagecreatetruecolor($thumb_width, $thumb_height);

// 保持PNG透明度，否则缩略图透明部分会变黑
if ($source_type == IMAGETYPE_PNG) {
    imagealphablending($thumb, false);
    imagesavealpha($thumb, true);
    $transparent = imagecolorallocatealpha($thumb, 255, 255, 255, 127);
    imagefilledrectangle($thumb, 0, 0, $thumb_width, $thumb_height, $transparent);
}


// 重新采样并复制图像的部分
imagecopyresampled($thumb, $source, 0, 0, 0, 0, $thumb_width, $thumb_height, $source_width, $source_height);

// 保存缩略图
imagejpeg($thumb, $thumb_image, 80); // 80是JPEG质量，可以调整

// 释放内存
imagedestroy($source);
imagedestroy($thumb);

echo "缩略图生成成功！";

?>

<?php

function createThumbnail($source_image, $thumb_image, $thumb_width, $thumb_height) {
    list($source_width, $source_height, $source_type) = getimagesize($source_image);

    // 计算缩放比例
    $width_ratio = $thumb_width / $source_width;
    $height_ratio = $thumb_height / $source_height;

    // 选择缩放比例，保证至少有一边与目标尺寸相等
    $ratio = max($width_ratio, $height_ratio);

    // 计算缩放后的尺寸
    $new_width = $source_width * $ratio;
    $new_height = $source_height * $ratio;

    // 计算裁剪位置
    $x = ($new_width - $thumb_width) / 2;
    $y = ($new_height - $thumb_height) / 2;

    switch ($source_type) {
        case IMAGETYPE_JPEG:
            $source = imagecreatefromjpeg($source_image);
            break;
        case IMAGETYPE_PNG:
            $source = imagecreatefrompng($source_image);
            break;
        case IMAGETYPE_GIF:
            $source = imagecreatefromgif($source_image);
            break;
        default:
            return false;
    }

    $thumb = imagecreatetruecolor($thumb_width, $thumb_height);

    if ($source_type == IMAGETYPE_PNG) {
        imagealphablending($thumb, false);
        imagesavealpha($thumb, true);
        $transparent = imagecolorallocatealpha($thumb, 255, 255, 255, 127);
        imagefilledrectangle($thumb, 0, 0, $thumb_width, $thumb_height, $transparent);
    }

    // 创建一个中间图像资源，用于缩放
    $intermediate = imagecreatetruecolor($new_width, $new_height);

    if ($source_type == IMAGETYPE_PNG) {
        imagealphablending($intermediate, false);
        imagesavealpha($intermediate, true);
        $transparent = imagecolorallocatealpha($intermediate, 255, 255, 255, 127);
        imagefilledrectangle($intermediate, 0, 0, $new_width, $new_height, $transparent);
    }

    imagecopyresampled($intermediate, $source, 0, 0, 0, 0, $new_width, $new_height, $source_width, $source_height);

    // 从中间图像资源裁剪到缩略图资源
    imagecopyresampled($thumb, $intermediate, 0, 0, $x, $y, $thumb_width, $thumb_height, $thumb_width, $thumb_height);


    imagejpeg($thumb, $thumb_image, 80);

    imagedestroy($source);
    imagedestroy($thumb);
    imagedestroy($intermediate);

    return true;
}

?>

<?php

try {
    $image = new Imagick('path/to/your/image.jpg');

    $image->thumbnailImage(200, 150, true); // true表示保持比例

    $image->writeImage('path/to/your/thumb.jpg');

    $image->destroy();

    echo "缩略图生成成功！";

} catch (ImagickException $e) {
    echo "Error: " . $e->getMessage();
}

?>

thumbnailImage()